U.S. Department of Transportation
Federal Highway Administration
1200 New Jersey Avenue, SE
Washington, DC 20590
2023664000
Federal Highway Administration Research and Technology
Coordinating, Developing, and Delivering Highway Transportation Innovations
REPORT 
This report is an archived publication and may contain dated technical, contact, and link information 

Publication Number: FHWAHRT14020 Date: January 2015 
Publication Number: FHWAHRT14020 Date: January 2015 
A curve advisory sign was installed at Arizona treatment site SR 377 in September 2008 for the SB direction of travel. The site is about 15 miles southwest of Holbrook, AZ.
Table 55 shows the results for the speed control point, which is 0.5 miles upstream of the sign. The site has a dynamic curve display that was placed for the SB direction of traffic. Speeds decreased at the control site from the before to the 1month and 12month after periods. This suggests that speeds overall may have decreased independent of the sign.
Table 55. Results for Arizona: SR 377 at 0.5 miles upstream (SB).
Before 
1 Mo 
Change 
12 Mo 
Change 
24 Mo 
Change 


ADT 
937 
898 
39 
826 
111 
822 
115 
Sample size 
2,061 
1,976 
NA 
1,817 
NA 
1,624 
NA 
Mean speed (mph) 
68.4 
65.6 
2.8 
65.8 
2.6 
66.3 
2.1 
SD of mean 
6.7 
6.0 
NA 
6.7 
NA 
6.3 
NA 
85th percentile speed (mph) 
74 
71 
3 
72 
2 
72 
2 
Fraction of vehicles exceeding posted or advisory speed limit 

By 5 mph 
40.0 
20.5 
48.8% 
25.1 
37.3% 
26.9 
32.8% 
By 10 mph 
14.5 
5.6 
61.4% 
6.0 
58.6% 
8.2 
43.4% 
By 15 mph 
5.2 
1.9 
63.5% 
1.7 
67.3% 
2.2 
57.7% 
By 20 mph 
1.8 
0.6 
66.7% 
0.4 
77.8% 
0.4 
77.8% 
ADT = Average daily traffic
NA = Not applicable
SD = Standard deviation
Table 56 shows the results at the PC. There was a significant decrease in all speed metrics for the 1, 12, and 24month after periods. The speed reduction was greater than that which occurred for the upstream control.
Mean speeds decreased in all cases by up to 5.6 mph, and 85th percentile speeds decreased by up to 8 mph.
There were also moderate decreases in the percent of vehicles exceeding the posted or advisory speed. Decreases of up to 33 percent occurred for vehicles exceeding by 5 mph or more, up to 17.8 percent for 10 mph or more over, up to 6.2 percent for 15 mph over, and up to 2.7 percent for 20 mph or more over. These represented a percent change of up to 96.4 percent.
Table 56. Results for Arizona: SR 377 at the PC (SB).
Before 
1 Mo 
Change 
12 Mo 
Change 
24 Mo 
Change 


Sample size 
2,292 
1,978 
NA 
1,793 
NA 
1,633 
NA 
Mean speed (mph) 
69.4 
63.8 
5.6 
65.8 
3.6 
64.7 
4.7 
SD of mean 
7.0 
5.0 
NA 
5.7 
NA 
5.7 
NA 
85th percentile speed (mph) 
76 
68 
8 
71 
5 
70 
6 
Fraction of vehicles exceeding posted or advisory speed limit 

By 5 mph 
0.41 
0.08 
79.9% 
0.23 
44.8% 
0.16 
60.3% 
By 10 mph 
0.20 
0.02 
91.3% 
0.04 
78.5% 
0.03 
86.2% 
By 15 mph 
0.07 
0.01 
92.5% 
0.01 
83.6% 
0.01 
91.0% 
By 20 mph 
0.03 
0.00 
96.4% 
0.00 
89.3% 
0.00 
92.9% 
NA = Not applicable
SD = Standard deviation
Table 57 presents results for the CC. Speeds decreased in most cases, but the decrease was smaller than that experienced at the upstream control location. Decreases were also smaller than at the PC. Decreases were larger for the 24month after period than for the 1 or 12month after period. Mean speed decreases resulted between 0.2 and 3.5 mph, with decreases in 85th percentile speed between 0 and 4 mph.
Table 57. Results for Arizona: SR 377 at the CC (SB).
Before 
1 Mo 
Change 
12 Mo 
Change 
24 Mo 
Change 


Sample size 
2,050 
2,026 
NA 
1,806 
NA 
1,633 
NA 
Mean speed (mph) 
66.5 
64.8 
1.7 
66.7 
0.2 
63.0 
3.5 
SD of mean 
6.2 
5.2 
NA 
5.4 
NA 
5.6 
NA 
85th percentile speed (mph) 
72 
69 
3 
72 
0 
68 
4 
Fraction of vehicles exceeding posted or advisory speed limit 

By 5 mph 
0.28 
0.131 
52.5% 
0.29 
4.3% 
0.08 
69.9% 
By 10 mph 
0.08 
0.03 
70.2% 
0.06 
26.2% 
0.01 
84.5% 
By 15 mph 
0.02 
0.01 
79.2% 
0.01 
58.3% 
0.01 
79.2% 
By 20 mph 
0.01 
0.00 
60.0% 
0.01 
0.0% 
0.00 
60.0%* 
*Not statistically significant at 95percent level of significance
NA = Not applicable
SD = Standard deviation
A speed feedback sign was installed at Arizona treatment site SR 95 in September 2008 for the SB direction of travel. The site is about 20 miles southeast of Lake Havasu City, AZ. Between the 12 and 24month after periods, the State installed other traffic calming devices at the curve independent of the team, as shown in figure 78. Results are presented for the 24month after period, but are noted as being unusual.
Figure 78. Photo. Additional traffic calming installed between 12 and 24 months at SR 95.
Table 58 shows the final results for the speed control point, which is 0.5 miles upstream of the sign.
Table 58. Results for Arizona: SR 95 at 0.5 miles upstream (SB).
Before 
1 Mo 
Change 
12 Mo 
Change 
24 Mo 
Change 


ADT 
2,682 
2,475 
207 
2,189 
493 
2,274 
408 
Sample size 
5,065 
4,867 
NA 
2,158 
NA 
4,477 
NA 
Mean speed (mph) 
65.2 
62.7 
2.5 
63.0 
2.2 
63.9 
1.3 
SD of mean 
6.0 
6.2 
NA 
5.8 
NA 
6.0 
NA 
85th percentile speed (mph) 
71 
69 
2 
68 
3 
69 
2 
Fraction of vehicles exceeding posted or advisory speed limit 

By 5 mph 
0.85 
0.71 
16.2% 
0.74 
12.2% 
0.79 
6.3% 
By 10 mph 
0.57 
0.39 
32.6% 
0.38 
33.5% 
0.48 
15.9% 
By 15 mph 
0.22 
0.12 
47.2% 
0.11 
51.8% 
0.15 
31.2% 
By 20 mph 
0.05 
0.03 
40.8% 
0.03 
49.0% 
0.03 
34.7% 
ADT = Average daily traffic
NA = Not applicable
SD = Standard deviation
The site has a dynamic speed display that was placed for the SB direction of traffic. Speeds decreased from the before period to 1month and 12month after periods at the control site. This suggests that speeds overall may have decreased independent of the signs.
Table 59 shows the results at the PC.
Table 59. Results for Arizona: SR 95 at the PC (SB).
Before 
1 Mo 
Change 
12 Mo 
Change 
24 Mo^{1} 
Change 


Sample size 
5,076 
4,814 
NA 
2,170 
NA 
4,460 
NA 
Mean speed (mph) 
57.2 
52.8 
4.4 
53.3 
3.9 
55.8 
1.4 
SD of mean 
5.4 
5.3 
NA 
5.9 
NA 
6.1 
NA 
85th percentile speed (mph) 
66 
58 
8 
59 
7 
63 
3 
Fraction of vehicles exceeding posted or advisory speed limit 

By 5 mph 
0.92 
0.75 
18.6% 
0.77 
16.9% 
0.86 
7.0% 
By 10 mph 
0.69 
0.32 
54.6% 
0.36 
48.8% 
0.58 
15.9% 
By 15 mph 
0.32 
0.09 
70.8% 
0.13 
58.9% 
0.25 
21.0% 
By 20 mph 
0.09 
0.03 
70.1% 
0.04 
57.5% 
0.08 
12.6% 
^{1}Additional traffic calming installed by Arizona DOT
NA = Not applicable
SD = Standard deviation
There was a significant decrease in all speed metrics for both the 1month and 12month after periods. The speed reduction was greater than that which occurred for the upstream control.
Mean speeds decreased by 4.4 and 3.9 mph, and 85th percentile speeds decreased by 8 and 7 mph. Moderate decreases occurred for the percent traveling 5, 10, 15, and 20 mph or more over the 45 mph advisory speed. The percent change in the fraction of vehicles traveling 15 or 20 mph or more over the advisory speed decreased by up to 70.8 percent.
At 24 months, speed reductions had also occurred, but they were lower than for 1month and 12month after periods, even though additional traffic calming had been installed.
Table 60 shows the results for the CC.
Table 60. Results for Arizona: SR 95 at the CC (SB).
Before 
1 Mo 
Change 
12 Mo 
Change 
24 Mo* 
Change 


Sample size 
5,042 
4,765 
4,338 
4173 
501 

Mean speed (mph) 
54.7 
49.4 
5.3 
51.8 
2.9 
50.6 
4.1 
SD of mean 
5.8 
5.0 
5.5 
5.8 


85th percentile speed (mph) 
61 
54 
7 
57 
4 
56 
5 
Fraction of vehicles exceeding posted or advisory speed limit 

by 5 mph 
0.82 
0.48 
41.5% 
0.68 
17.8% 
0.58 
29.6% 
by 10 mph 
0.51 
0.14 
73.3% 
0.30 
41.8% 
0.24 
53.8% 
by 15 mph 
0.20 
0.03 
85.6% 
0.08 
61.0% 
0.06 
69.2% 
by 20 mph 
0.05 
0.01 
88.9% 
0.02 
66.7% 
0.02 
66.7% 
*Additional traffic calming installed by Arizona DOT
NA = Not applicable
SD = Standard deviation
Speeds decreased for all speed metrics for both data collection periods, and the change was greater than the change at the control location. Decreases in mean speed were 5.3 and 2.9 mph, with a decrease in 85th percentile speed of 7 and 4 mph.
Moderate decreases were noted in the fraction of vehicles traveling 5, 10, 15, and 20 mph, with a percent change of almost 90 percent in the fraction of vehicles traveling 15 or 20 mph over the advisory speed. At 24 months, speed reductions were similar to the 1 and 12month after periods, even though additional traffic calming had been installed.
RESULTS FOR FLORIDASR 267 BY TALLAHASSEE
A curve warning sign was installed for the SB direction of traffic at Florida treatment site SR 267 in December 2008. The site is about 25 miles west of Tallahassee, FL. Table 61 shows the results for the speed control point, which is 0.5 miles upstream of the sign (dynamic curve display).
Table 61. Results for Florida: SR 267 upstream of curve (SB).
Before 
3 Mo 
Change 
12 Mo 
Change 
24 Mo 
Change 


ADT 
1,958 
1,899 
59 
1,682 
276 
1,713 
245 
Sample size 
3,783 
3,665 
NA 
3,250 
NA 
3,370 
NA 
Mean speed (mph) 
62.9 
67.4 
4.5 
56.3 
6.6 
61.0 
1.9 
SD of mean 
6.1 
6.8 
NA 
4.7 
NA 
5.30 
NA 
85th percentile speed (mph) 
68 
74 
6 
61 
7 
66 
2 
Fraction of vehicles exceeding posted or advisory speed limit 

By 5 mph 
0.75 
0.91 
21.7% 
0.22 
70.8% 
0.60 
19.0% 
By 10 mph 
0.35 
0.67 
91.4% 
0.05 
87.1% 
0.23 
33.2% 
By 15 mph 
0.11 
0.34 
196.5% 
0.01 
90.3% 
0.05 
54.0% 
By 20 mph 
0.04 
0.13 
277.1% 
0.00 
91.4% 
0.01 
62.9% 
ADT = Average daily traffic
NA = Not applicable
SD = Standard deviation
The team collected data 3 months rather than 1 month after the signs were installed because they experienced problems with the signs at the 1 month after period. Speeds increased from the before period to 3month after period, and decreased for the 12month and 24month after periods. The speeds in the 12month after period for the control site appear to be unusually low, although there were no known reasons this may have occurred.
Table 62 shows results for the PC. Minor decreases occurred in the various speed metrics for the 3month and 24month after period, while a very large decrease in mean (6.5 mph) and 85th percentile (8 mph) occurred for the 12month after period. However, as noted, very large decreases also occurred for the control site for the 12month after period. Mean speeds decreased by 6.5 mph while the 85th percentile speed decreased by 8 mph.
Minor decreases in the fraction of vehicles traveling 5, 10, 15, or 20 mph over the posted speed limit of 55 mph occurred. However, the magnitude of the differences was significant, with percent changes up to 100 percent noted.
Table 62. Results for Florida: SR 267 at the PC (SB).
Before 
3 Mo 
Change 
12 Mo 
Change 
24 Mo 
Change 


Sample size 
3,782 
3697 
NA 
3,285 
NA 
1,998 
NA 
Mean speed (mph) 
54.3 
53.4 
0.9 
47.8 
6.5 
53.2 
1.1 
SD of mean 
5.7 
5.7 
NA 
4.8 
NA 
5.7 
NA 
85th percentile speed (mph) 
60 
59 
1 
52 
8 
59 
1 
Fraction of vehicles exceeding posted or advisory speed limit 

By 5 mph 
0.15 
0.12 
20.9% 
0.01 
95.4% 
0.10 
32.0% 
By 10 mph 
0.03 
0.02 
25.0% 
0.00 
96.4% 
0.01 
60.7% 
By 15 mph 
0.01 
0.00 
57.1% 
0.0 
100.0% 
0.00 
71.4% 
By 20 mph 
0.00 
0.00 
0.0% 
0.0 
100.0% 
0.00 
100.0%* 
*Not statistically significant at 95percent level of significance
NA = Not applicable
SD = Standard deviation
Table 63 shows results for the CC. Modest decreases occurred for all of the after periods. Decreases for the 12month after period are smaller than the decreases that occurred at the control site. Moderate decreases also occurred for the fraction of vehicles traveling 5, 10, 15, and 20 mph over the posted speed limit.
Table 63. Results for Florida: SR 267 at the CC (SB).
Before 
3 Mo 
Change 
12 Mo 
Change 
24 Mo 
Change 


Sample size 
3,770 
3,711 
NA 
3,098 
NA 
2,015 
NA 
Mean speed (mph) 
53.2 
52.5 
0.7 
51.3 
1.9 
52.4 
0.8 
SD of mean 
6 
5.9 
NA 
5.8 
NA 
5.6 
NA 
85th percentile speed (mph) 
59 
58 
1 
57 
2 
58 
1 
Fraction of vehicles exceeding posted or advisory speed limit 

By 5 mph 
0.12 
0.10 
17.2% 
0.07 
41.8% 
0.09 
23.8% 
By 10 mph 
0.02 
0.02 
28.6% 
0.01 
42.9% 
0.01 
66.7% 
By 15 mph 
0.00 
0.00 
50.0% 
0.00 
50.0% 
0.00 
100.0% 
By 20 mph 
0.00 
0.00 
N/A 
0.00 
N/A 
0.00 
N/A 
NA = Not applicable
SD = Standard deviation
RESULTS FOR FLORIDAUS 20 BY TALLAHASSEE
A curve advisory speed sign was installed WB on US 20 by Tallahassee. The sign was installed in December 2008. The site is about 12 miles west of Tallahassee, FL. Table 64 shows the results for the speed control point, which is 0.5 miles upstream of the sign.
Table 64. Results for Florida: US 20 by Tallahassee upstream of curve (WB).
Before 
3 Mo 
Change 
12 Mo 
Change 
24 Mo 
Change 


ADT 
2,100 
3,685 
1,585 
3,327 
1,227 
3,248 
1,148 
Sample size 
6,193 
7,232 
NA 
6,542 
NA 
6,713 
NA 
Mean speed (mph) 
58.1 
56.4 
1.7 
58.9 
0.8 
56.9 
1.2 
SD of mean 
5.2 
5.0 
NA 
5.5 
NA 
5.2 
NA 
85th percentile speed (mph) 
63 
61 
2 
64 
1 
61 
2 
Fraction of vehicles exceeding posted or advisory speed limit 

By 5 mph 
0.37 
0.22 
39.2% 
0.46 
25.9% 
0.28 
24.8% 
By 10 mph 
0.08 
0.03 
57.1% 
0.11 
48.1% 
0.05 
40.3% 
By 15 mph 
0.02 
0.01 
53.3% 
0.02 
46.7% 
0.01 
46.7% 
By 20 mph 
0.01 
0.00 
80.0% 
0.00 
20.0% 
0.00 
40.0%* 
*Not statistically significant at 95percent level of significance
ADT = Average daily traffic
NA = Not applicable
SD = Standard deviation
Data were collected 3 months after the signs were installed rather than 1 month because the signs experienced problems at the 1month after period. Speeds at the control point decreased from the before period to the 3month after period, and increased for the 12month after period by a small amount. Moderate decreases occurred at the 24month after period, which were similar to the 3month after period.
Table 65 provides results for US 20 at the PC. Modest decreases occurred for the 3month, 12month, and 24month after periods for all speed metrics. Modest speed changes occurred for the mean and 85th percentile speeds, which were similar to the decreases noted for the control period. Moderate changes occurred for the fraction of vehicles that exceeded the 55 mph speed limit.
Table 66 shows results for the CC. Moderate decreases occurred for all after periods, with a decrease of about 3 mph for both the mean and 85th percentile speeds at 3 months; a decrease of almost 23 percent occurred from the 3month after period for vehicles traveling 5 mph over the 55 mph posted speed limit. Moderate decreases also occurred for the 12month after period, with a 1 mph decrease in mean and 85th percentile speeds. Decreases of 2 mph occurred for the mean and 85th percentile speeds at the 24month after period.
Moderate decreases in the fraction of vehicles traveling 5, 10, 15, or 20 mph or more over the posted speed limit occurred, which resulted in percent changes of up to 80 percent.
Table 65. Results for Florida: US 20 by Tallahassee at the PC (WB).
Before 
3 Mo 
Change 
12 Mo 
Change 
24 Mo 
Change 


Sample size 
5,964 
7,049 
NA 
6,403 
NA 
6487 
NA 
Mean speed (mph) 
57.3 
55.9 
1.4 
55.4 
1.9 
56.2 
1.1 
SD of mean 
4.3 
4.5 
NA 
4.5 
NA 
5.2 
NA 
85th percentile speed (mph) 
61 
60 
1 
59 
2 
60 
1 
Fraction of vehicles exceeding posted or advisory speed limit 

By 5 mph 
0.26 
0.18 
31.1% 
0.14 
45.5% 
0.20 
22.6% 
By 10 mph 
0.05 
0.03 
34.8% 
0.02 
50.0% 
0.06 
37.0% 
By 15 mph 
0.01 
0.01 
44.4% 
0.01 
44.4% 
0.02 
122.2% 
By 20 mph 
0.00 
0.00 
0.0%* 
0.00 
50.0% 
0.01 
150.0% 
*Not statistically significant at 95percent level of significance
NA = Not applicable
SD = Standard deviation
Table 66. Results for Florida: US 20 by Tallahassee at the CC (WB).
Before 
3 Mo 
Change 
12 Mo 
Change 
24 Mo 
Change 


Sample size 
5,964 
7,014 
NA 
6,342 
NA 
6,487 
NA 
Mean speed (mph) 
58.2 
55.3 
2.9 
57.1 
1.1 
56.1 
2.1 
SD of mean 
4.3 
4.3 
NA 
4.5 
NA 
4.4 
NA 
85th percentile speed (mph) 
62 
59 
3 
61 
1 
60 
2 
Fraction of vehicles exceeding posted or advisory speed limit 

By 5 mph 
0.36 
0.12 
65.4% 
0.25 
29.6% 
0.18 
48.6% 
By 10 mph 
0.07 
0.02 
78.3% 
0.04 
40.6% 
0.02 
66.7% 
By 15 mph 
0.01 
0.00 
70.0% 
0.01 
40.0% 
0.00 
60.0% 
By 20 mph 
0.00 
0.00 
50.0% 
0.00 
50.0% 
0.00 
0.0%* 
*Not statistically significant at 95percent level of significance
NA = Not applicable
SD = Standard deviation
RESULTS FOR FLORIDAUS 20 BY GAINESVILLE
The Florida US 20 site near Gainesville has a dynamic speed display for the EB direction of traffic. The site is 26 miles east of Gainesville, FL. The advisory speed is 45 mph with a tangent speed of 55 mph. Table 67 presents results for the upstream speed control site.
Table 67. Results for Florida: US 20 Gainesville upstream of curve (EB).
Before 
1 Mo 
Change 
12 Mo 
Change 
24 Mo 
Change 


ADT 
2,816 
3,031 
215 
2,985 
169 
3,077 
261 
Sample 
5,504 
5,953 
NA 
5,829 
NA 
6,041 
NA 
Mean speed (mph) 
55.6 
59.5 
3.9 
55.1 
0.5 
55.4 
0.2* 
SD of mean 
6.0 
6.6 
NA 
5.9 
NA 
6.3 
NA 
85th percentile speed (mph) 
61 
65 
4 
60 
1 
61 
0 
Fraction of vehicles exceeding posted or advisory speed limit 

By 5 mph 
0.23 
0.52 
126.6% 
0.19 
17.9% 
0.22 
3.9%* 
By 10 mph 
0.05 
0.20 
319.1% 
0.03 
27.7% 
0.04 
17.0%* 
By 15 mph 
0.01 
0.05 
455.6% 
0.01 
22.2%* 
0.01 
0.0%* 
By 20 mph 
0.00 
0.01 
300.0% 
0.00 
0.0%* 
0.00 
33.3%* 
*Not statistically significant at 95percent level of significance
ADT = Average daily traffic
NA = Not applicable
SD = Standard deviation
As shown, speed metrics increased significantly for the 1month after period, while minor decreases were noted for the 12month after period. Little change was noted for the 24month after period at the control site. The decrease for vehicles exceeding the posted speed limit of 55 by 15 and 20 mph were not statistically significant at the 90percent level of significance.
Table 68 shows changes in speed metrics for the PC. Speeds increased for the 1month after period, with an increase of 3.3 mph and 4.0 mph for the mean and 85th percentile speed, respectively. However, this is similar to the increase that was noted for the control location.
Moderate decreases were noted for the 12month after period, with a decrease of almost 3 mph for the mean and 4 mph for the 85th percentile speed. Significant decreases were observed for the percent change in vehicles exceeding the advisory speed by 5, 10, 15, and 20 mph. These results suggest that the sign had a large impact on highend speeds at the 12month data collection period.
Moderate decreases also occurred for the 24month after period. It is not known why speeds increased at 3 months but decreased at 12 and 24 months.
Table 69 provides results for the CC. Significant decreases occurred for both the 1 and 12month after period. A decrease of about 4 mph occurred for the mean and 85th percentile speeds for both time periods. Large decreases in the percent of vehicles exceeding the advisory speed were noted, with a large decrease in the percent of vehicle exceeding the advisory speed by 15 and 20 mph. Only moderate decreases were noted for the 24month after period. Decreases were greater at the CC as compared with the PC.
Table 68. Results for Florida: US 20 Gainesville at the PC (EB).
Before 
3 Mo 
Change 
12 Mo 
Change 
24 Mo 
Change 


Sample 
5,490 
5,904 
NA 
5,861 
NA 
6,046 
NA 
Mean (mph) 
57.8 
61 
3.3 
55.0 
2.8 
56.7 
1.1 
SD of mean 
6.0 
6.5 
NA 
5.2 
NA 
5.2 
NA 
85th percentile speed (mph) 
63 
67 
4 
59 
4 
61 
2 
Fraction of vehicles exceeding posted or advisory speed limit 

By 5 mph 
0.93 
0.96 
2.8% 
0.90 
3.6% 
93.5 
0.1%* 
By 10 mph 
0.76 
0.89 
16.0% 
0.58 
24.7% 
70.9 
7.2% 
By 15 mph 
0.38 
0.66 
71.3% 
0.14 
64.2% 
25.6 
33.2% 
By 20 mph 
0.10 
0.26 
172.9% 
0.02 
77.1% 
5.3 
44.8% 
*Not statistically significant at 95percent level of significance
NA = Not applicable
SD = Standard deviation
Table 69. Results for Florida: US 20 Gainesville at the CC (EB).
Before 
3 Mo 
Change 
12 Mo 
Change 
24 Mo 
Change 


Sample size 
5,496 
5,897 
NA 
5,878 
NA 
6,062 
NA 
Mean speed (mph) 
58.2 
54.5 
3.7 
54.5 
3.7 
57.0 
1.2 
SD of mean 
5.8 
5.1 
NA 
5.5 
NA 
5.8 
NA 
85th percentile speed (mph) 
63 
59 
4 
59 
4 
62 
1 
Fraction of vehicles exceeding posted or advisory speed limit 

By 5 mph 
0.95 
0.88 
7.1% 
0.89 
6.5% 
0.94 
1.1% 
By 10 mph 
0.79 
0.62 
21.2% 
0.54 
32.0% 
0.74 
6.3% 
By 15 mph 
0.41 
0.12 
69.9% 
0.12 
70.2% 
0.29 
28.1% 
By 20 mph 
0.10 
0.02 
80.4% 
0.02 
80.4% 
0.06 
40.2% 
NA = Not applicable
SD = Standard deviation
A curve display sign was installed at the US 30 site for the EB direction of traffic in November 2008. No advisory speeds are present with a tangent speed of 55 mph. The site was 4 miles west of Tama, IA. Data were not collected at the 1month after period because of adverse winter weather conditions, but are reported for 3 months after instead. Table 70 provides results for the upstream speed control location. All speed metrics decreased for all after time periods, which may suggest that speeds decreased overall independent of the sign.
Table 70. Results for Iowa: US 30 upstream (EB).

Before 
3 Mo 
Change 
12 Mo 
Change 
24 Mo 
Change 

ADT 
5,506 
4,408 
1,098 
4,578 
928 
5,221 
285 
Sample size 
9,176 
8,589 
NA 
8,878 
NA 
5,064 
NA 
Mean speed (mph) 
58.0 
54.8 
3.2 
54.2 
3.8 
56.5 
1.5 
SD of mean 
6.1 
4.9 
NA 
5.6 
NA 
5.2 
NA 
85th percentile speed (mph) 
63 
59 
4 
59 
4 
61 
2 
Fraction of vehicles exceeding posted or advisory speed limit 

By 5 mph 
0.40 
0.12 
69.0% 
0.11 
71.5% 
0.26 
35.5% 
By 10 mph 
0.08 
0.01 
86.3% 
0.01 
85.0% 
0.04 
53.8% 
By 15 mph 
0.02 
0.00 
87.5% 
0.00 
87.5% 
0.01 
68.8% 
By 20 mph 
0.01 
0.00 
100.0% 
0.00 
100.0% 
0.00 
85.7% 
ADT = Average daily traffic
NA = Not applicable
SD = Standard deviation
Table 71 shows results for at the PC for US 30. As indicated, speeds also decreased for all after time periods for all speed metrics. However, the decreases were generally within the range of those noted for the control site.
Table 71. Results for Iowa: US 30 at the PC (EB).

Before 
3 Mo 
Change 
12 Mo 
Change 
24 Mo 
Change 

Sample size 
9,258 
8,646 
NA 
8,805 
NA 
5,051 
NA 
Mean speed (mph) 
58.9 
58.0 
0.9 
56.4 
2.5 
58.1 
0.8 
SD of mean 
4.5 
4.1 
NA 
4.5 
NA 
4.1 
NA 
85th percentile speed (mph) 
63 
62 
1 
60 
3 
62 
1 
Fraction of vehicles exceeding posted or advisory speed limit 

by 5 mph 
0.46 
0.37 
19.5% 
0.21 
53.2% 
0.36 
21.4% 
by 10 mph 
0.08 
0.04 
44.2% 
0.02 
76.6% 
0.04 
50.6% 
by 15 mph 
0.01 
0.01 
37.5% 
0.00 
62.5% 
0.01 
25.0% 
by 20 mph 
0.00 
0.00 
100.0% 
0.00 
0.0%* 
0.00 
0.0%* 
*Not statistically significant at 95percent level of significance
NA = Not applicable
SD = Standard deviation
Table 72 provides speed metrics at the CC for the Iowa US 30 site. Decreases were noted for the 3 and 24month after periods. However, speeds increased for the 12month after period.
Table 72. Results for Iowa: US 30 at the CC (EB).

Before 
3 Mo 
Change 
12 Mo 
Change 
24 Mo 
Change 

Sample size 
9,223 
5,630 
NA 
1,181 
NA 
5,078 
NA 
Mean speed (mph) 
59.4 
57.9 
1.5 
59.8 
0.4 
57.4 
2.0 
SD of mean 
4.6 
4.6 
NA 
6.0 
NA 
4.3 
NA 
85th percentile speed (mph) 
63 
62 
1 
66 
3 
61 
2 
Fraction of vehicles exceeding posted or advisory speed limit 

By 5 mph 
0.50 
0.37 
25.6% 
0.61 
22.0% 
0.28 
44.0% 
By 10 mph 
0.10 
0.04 
58.2% 
0.13 
29.6% 
0.03 
67.3% 
By 15 mph 
0.01 
0.00 
63.6% 
0.01 
9.1% 
0.01 
54.5% 
By 20 mph 
0.00 
0.00 
50.0% 
0.00 
50.0% 
0.00 
50.0% 
NA = Not applicable
SD = Standard deviation
Changes were similar to those experienced at the upstream control site. Speeds decreased at the control site for those time periods so the control site does not indicate a trend of speed increase, which might explain the phenomenon. Speeds at the 24month after period are similar to those for the 3month after period, with about a 1 mph decrease in mean and 85th percentile speeds up to a 10percent decrease in vehicles traveling over the posted speed limit.
Table 73 provides results for the upstream speed control site at US 67 in Iowa, which has a dynamic speed display for the SB direction of traffic, installed in November 2008. The posted speed limit is 55 mph, and no advisory speed is present. The site is 15 miles northeast of Bettendorf, IA.
A very large increase was noted for all speed metrics for the 1month after period at the control site. However, no pattern was observed regarding increases or decreases for the other after periods. Both minor decreases and increases were noted.
Table 73. Results for Iowa: US 67 upstream (SB).

Before 
1 Mo 
Change 
12 Mo 
Change 
24 Mo 
Change 

ADT 
1,891 
1,985 
94 
1,882 
9 
1,886 
5 
Sample size 
3,728 
3,820 
NA 
3,639 
NA 
3,690 
NA 
Mean speed (mph) 
52.6 
67.5 
14.9 
52.1 
0.5 
52.8 
0.2* 
SD of mean 
7.3 
9.2 
NA 
7.9 
NA 
8.1 
NA 
85th percentile speed (mph) 
58 
75 
17 
58 
0 
59 
1 
Fraction of vehicles exceeding posted or advisory speed limit 

By 5 mph 
0.10 
0.74 
† 
0.10 
10% 
0.13 
31% 
By 10 mph 
0.01 
0.71 
† 
0.01 
11%* 
0.01 
11% 
By 15 mph 
0.00 
0.43 
† 
0.00 
50%* 
0.00 
50%* 
By 20 mph 
0.00 
0.18 
† 
0.00 
100% 
0.00 
100%* 
*Not statistically significant at 95percent level of significance
†Owing to abnormally high speeds for the 1month after period, percent change was very large (> 700 percent)
ADT = Average daily traffic
NA = Not applicable
SD = Standard deviation
Table 74 shows results for the data collection point at the PC. Modest decreases occurred for most of the speed metrics with the largest decreases occurring at the 24month after period.
Table 74. Results for Iowa: US 67 at the PC (SB).

Before 
1 Mo 
Change 
12 Mo 
Change 
24 Mo 
Change 

Sample size 
4,334 
3,818 
NA 
3,703 
NA 
3,779 
NA 
Mean speed (mph) 
57.6 
56.8 
0.8 
56.6 
1.0 
55.2 
2.4 
SD of mean 
5.3 
5.0 
NA 
4.8 
NA 
4.8 
NA 
85th percentile speed (mph) 
62 
61 
1 
61 
1 
59 
3 
Fraction of vehicles exceeding posted or advisory speed limit 

By 5 mph 
32.1 
25.8 
19.6% 
22.4 
30.2% 
13.5 
57.9% 
By 10 mph 
7.2 
4.1 
43.1% 
3.9 
45.8% 
2.0 
72.2% 
By 15 mph 
1.4 
0.8 
42.9% 
0.8 
42.9% 
0.4 
71.4% 
By 20 mph 
0.3 
0.1 
66.7% 
0.2 
33.3% 
0.1 
66.7%* 
*Not statistically significant at 95percent level of significance
NA = Not applicable
SD = Standard deviation
Decreases in mean speed ranged from 0.8 to 2.4 mph, and decreases in 85th percentile speed were 1 to 3 mph. Significant decreases occurred in the fraction of vehicles exceeding the tangent speed limit of 55 mph by 5, 10, and 15 mph or more. The percent change was most significant for vehicles traveling 20 mph or more over limit, with percent changes up to 67 percent. Decreases were usually greater than those at the control site for the corresponding time period.
Table 75 shows results for the CC. Unlike the PC, large decreases were noted for all time periods in the after period. Reductions up to 11 mph for mean speed and 12 mph for the 85th percentile speeds were noted. Large decreases in the number of vehicles exceeding the posted speed limit of 55 mph occurred. A 100percent change in the fraction of vehicles over the posted speed limit was noted for all of the 1month intervals, three of the 12month intervals, and three of the 24month intervals. Decreases were much greater at the CC than at the PC.
Table 75. Results for Iowa: US 67 at the CC (SB).

Before 
1 Mo 
Change 
12 Mo 
Change 
24 Mo 
Change 

Sample size 
3,822 
3,791 
NA 
3,691 
NA 
3,764 
NA 
Mean speed 
63.1 
52.2 
10.9 
55.2 
7.9 
56.1 
7.0 
SD of mean 
5.5 
4.3 
NA 
4.6 
NA 
4.6 
NA 
85th percentile speed 
68 
56 
12 
59 
9 
60 
8 
By 5 mph 
0.78 
0.03 
96.5% 
0.148 
82.2% 
0.20 
74.1% 
By 10 mph 
0.38 
0.00 
99.0% 
0.02 
94.8% 
0.02 
93.7% 
By 15 mph 
0.10 
0.00 
97.9% 
0.00 
96.9% 
0.00 
97.9% 
By 20 mph 
0.02 
0.00 
95.2% 
0.00 
95.2% 
0.00 
100.0% 
NA = Not applicable
SD = Standard deviation
A dynamic curve display was installed at US 69 for the NB direction of traffic. The posted speed limit is 55 mph, and the curve has an advisory speed of 50 mph. The site is 29 miles south of Des Moines, IA. The sign was installed in April 2009.
Table 76 shows results for the upstream (speed control) location. Minor decreases were noted for all after periods. Most of the changes in the fraction of vehicles traveling over the advisory speed were not statistically significant.
Table 76. Results for Iowa: US 69 upstream (NB).

Before 
1 Mo 
Change 
12 Mo 
Change 
24 Mo 
Change 

ADT 
750 
808 
58 
808 
58 
715 
35 
Sample size 
1,482 
1,600 
NA 
1,604 
NA 
1415 
NA 
Mean speed (mph) 
57.1 
56.7 
0.4 
56.7 
0.4 
56.1 
1 
SD of mean 
5.9 
5.8 
NA 
6.1 
NA 
6.5 
NA 
85th percentile speed (mph) 
62 
61 
1 
62 
0 
61 
1 
Fraction of vehicles exceeding posted or advisory speed limit 

By 5 mph 
0.32 
0.28 
11% 
0.30 
6%* 
0.26 
17.4% 
By 10 mph 
0.06 
0.05 
17% 
0.07 
13%* 
0.06 
6.3%* 
By 15 mph 
0.01 
0.01 
8% 
0.01 
8%* 
0.01 
8.3%* 
By 20 mph 
0.00 
0.00 
0%* 
0.00 
33%* 
0.01 
66.7%* 
*Not statistically significant at 95percent level of significance
ADT = Average daily traffic
NA = Not applicable
SD = Standard deviation
Table 77 shows speed metrics for the PC. Minor decreases were noted for the 1 and 12month after periods, but were within the range of decrease noted for the control location. Moderate decreases occurred for the 24month after period with a decrease of 2.7 mph in mean speed and 2 mph for 85th percentile speed.
Table 77. Results for Iowa: US 69 the PC (NB).

Before 
1 Mo 
Change 
12 Mo 
Change 
24 Mo 
Change 

Sample size 
1,574 
1,832 
NA 
1,674 
NA 
1,513 
NA 
Mean speed (mph) 
56.8 
56.6 
0.2 
55.5 
1.3 
54.1 
2.7 
SD of mean 
5.4 
4.5 
NA 
6.1 
NA 
5.2 
NA 
85th percentile speed (mph) 
61 
61 
0 
61 
0 
59 
2 
Fraction of vehicles exceeding posted or advisory speed limit 

By 5 mph 
0.73 
0.71 
3.1% 
0.63 
13.7% 
0.47 
35.2% 
By 10 mph 
0.29 
0.25 
14.3% 
0.23 
19.9% 
0.12 
58.5% 
By 15 mph 
0.05 
0.04 
24.5% 
0.04 
28.6% 
0.02 
61.2% 
By 20 mph 
0.01 
0.01 
25.0% 
0.01 
37.5% 
0.00 
87.5% 
NA = Not applicable
SD = Standard deviation
Vehicles traveling 5 mph over the advisory speed of 50 mph by 35 percent and the fraction traveling 10 mph over decreased 58.5 percent. Vehicles traveling 15 mph over the advisory speed limit decreased by only 3.0 percent, but this represented a 61percent decrease; the fraction traveling 20 mph or more over the speed limit decreased 87.5 percent.
Decreases were greater for the 24month after period than for the previous two after periods, with a 2.7 and 2 mph decrease in mean and 85th percentile speeds. Significant decreases in the percent of vehicles traveling over the 50 mph advisory speed were also noted.
Similar decreases were noted for the CC as for the PC as shown in table 78. Modest decreases occurred for all speed metrics for the 1month after period, but moderate decreases were noted for the 12 and 24month after periods.
Table 78. Results for Iowa: US 69 at the CC (NB).

Before 
1 Mo 
Change 
12 Mo 
Change 
24 Mo 
Change 

Sample size 
1,573 
1,666 
NA 
1,659 
NA 
1,509 
NA 
Mean speed (mph) 
56.1 
56.1 
0.0 
53.6 
2.5 
54.8 
1.3 
SD of mean 
4.8 
5.1 
NA 
5.3 
NA 
5.8 
NA 
85th percentile speed (mph) 
60 
61 
1 
58 
2 
60 
0 
Fraction of vehicles exceeding posted or advisory speed limit 

By 5 mph 
0.68 
0.66 
2.5% 
0.47 
30.5% 
0.55 
19.3% 
By 10 mph 
0.22 
0.22 
0.4% 
0.10 
59.6% 
0.17 
22.9% 
By 15 mph 
0.02 
0.00 
95.8% 
0.01 
70.8% 
0.02 
12.5%* 
By 20 mph 
0.00 
0.00 
100.0% 
0.00 
100.0% 
0.00 
0.0%* 
*Not statistically significant at 95percent level of significance
NA = Not applicable
SD = Standard deviation
A speed display was installed at Iowa 136 for the NB direction of traffic in April 2009. The site has a posted speed limit of 50 mph and an advisory speed of 45 mph. The site is 7 miles northwest of Clinton, IA.
Table 79 shows results for the upstream speed control site. Significant increases occurred for the 1month after period, with minor decreases in the 12month and 24month after period.
Table 79. Results for Iowa: Iowa 136 upstream (NB).

Before 
1 Mo 
Change 
12 Mo 
Change 
24 Mo 
Change 

ADT 
621 
715 
94 
746 
125 
642 
21 
Sample size 
1,228 
1,365 
NA 
1,480 
NA 
1,278 
50 
Mean speed 
53.0 
60.2 
7.2 
52.7 
0.3 
51.6 
1.4 
SD of mean 
7.62 
10.8 
NA 
6.6 
1.0 
8 
NA 
85th percentile speed 
59 
71 
12 
58 
1.0 
58 
1 
Fraction of vehicles exceeding posted or advisory speed limit 

By 5 mph 
0.43 
0.68 
58% 
0.40 
6.1% 
0.37 
14.7% 
By 10 mph 
0.14 
0.52 
280% 
0.11 
23.4% 
0.10 
26.3% 
By 15 mph 
0.04 
0.34 
* 
0.02 
59.5% 
0.01 
67.6% 
By 20 mph 
0.01 
0.19 
* 
0.00 
66.7% 
0.00 
66.7% 
*Change in excess of 300 percent
ADT = Average daily traffic
NA = Not applicable
SD = Standard deviation
As noted in table 80, moderate decreases in speed resulted for all time periods for all speed metrics at the PC for Iowa 136. Decreases up to 3 mph in mean and up to 4 mph for 85th percentile speed occurred. The reduction in the fraction of vehicles exceeding the advisory speed of 45 mph was up to 17 percent for 5 mph over, up to 58 percent for 10 mph, up to 72 percent for 15 mph, and up to 89 percent for 20 mph.
Table 80. Results for Iowa: Iowa 136 at the PC (NB).

Before 
1 Mo 
Change 
12 Mo 
Change 
24 Mo 
Change 

Sample size 
1,174 
1,327 
NA 
1,417 
NA 
1,228 
NA 
Mean speed (mph) 
53.6 
50.9 
2.7 
52.3 
0.8 
51.5 
2.1 
SD of mean 
6.0 
5.0 
NA 
6.1 
NA 
5.8 
NA 
85th percentile speed (mph) 
59 
55 
4 
58 
1 
57 
2 
Fraction of vehicles exceeding posted or advisory speed limit 

By 5 mph 
0.79 
0.65 
16.8% 
0.76 
2.8% 
0.68 
13.1% 
By 10 mph 
0.44 
0.18 
57.9% 
0.34 
22.2% 
0.27 
38.7% 
By 15 mph 
0.14 
0.04 
71.9% 
0.10 
31.5% 
0.07 
52.5% 
By 20 mph 
0.04 
0.01 
73.0% 
0.02 
52.3% 
0.00 
89.2% 
NA = Not applicable
SD = Standard deviation
Table 81 shows speed metrics for the CC at Iowa 136. Moderate decreases in average speed and 85th speed resulted at the CC for the 1, 12, and 24month after periods. Moderate changes in the percent of vehicles traveling 5, 10, 15, or 20 mph or more over the advisory speed occurred for all the after periods.
Table 81. Results for Iowa: Iowa 136 at the CC (NB).

Before 
1 Mo 
Change 
12 Mo 
Change 
24 Mo 
Change 

Sample size 
1,178 
1,324 
NA 
1,345 
NA 
628 
NA 
Mean speed (mph) 
52.2 
51.6 
0.6 
50.2 
2.0 
50.7 
1.5 
SD of mean 
5.8 
5.2 
NA 
5.8 
NA 
6.6 
NA 
85th percentile speed (mph) 
58 
56 
2 
55 
3 
57 
1 
Fraction of vehicles exceeding posted or advisory speed limit 

By 5 mph 
0.71 
0.70 
1.5% 
0.59 
17.0% 
0.65 
9.2% 
By 10 mph 
0.34 
0.24 
28.6% 
0.19 
44.8% 
0.25 
25.4% 
By 15 mph 
0.09 
0.05 
40.2% 
0.03 
64.4% 
0.05 
44.8% 
By 20 mph 
0.02 
0.01 
43.8% 
0.00 
75.0% 
0.01 
68.8% 
NA = Not applicable
SD = Standard deviation
A dynamic speed sign was installed for Alkire Road in Ohio. The curve has an advisory speed of 30 mph with a speed limit of 55 mph. The sign was installed for the EB direction of traffic. The site is located about 16 miles southwest of Columbus, OH. Table 82 shows results for the upstream speed control location.
Table 82. Results for Ohio: Alkire Road upstream of curve (EB).
Before 
1 Mo 
Change 
12 Mo 
Change 
24 Mo 
Change 


ADT 
1,450 
1,519 
69 
1,490 
40 
1,486 
36 
Sample size 
2,863 
3,005 
NA 
1,476 
NA 
2,913 
NA 
Mean speed (mph) 
52.7 
58.8 
6.1 
51.3 
1.4 
50.1 
2.6 
SD of mean 
6.9 
8 
NA 
7.7 
NA 
7.9 
NA 
85th percentile speed (mph) 
59 
66 
7 
58 
1 
57 
2 
Fraction of vehicles exceeding posted or advisory speed limit 

By 5 mph 
0.14 
0.45 
2.1% 
0.11 
21.8% 
0.08 
44.4% 
By 10 mph 
0.04 
0.20 
4.0% 
0.02 
40.0% 
0.02 
50.0% 
By 15 mph 
0.01 
0.08 
7.2% 
0.01 
50.0% 
0.01 
30.0%* 
By 20 mph 
0.00 
0.03 
14.0% 
0.00 
50.0%* 
0.00 
0.0%* 
*Not statistically significant at 95percent level of significance
ADT = Average daily traffic
NA = Not applicable
SD = Standard deviation
Minor decreases were noted for the PC as shown in table 83. Minor reductions resulted in the fraction of vehicles traveling 5 mph or more over the advisory speed of 30 mph occurred (up to 7.9 percent). Moderate reductions were noted in the percent of vehicles exceeding the advisory speed of 30 mph by 10 mph or more for all of the after periods, with decreases up to 25.1 percent. Moderate decreases were also noted in the percent of vehicles traveling 15 mph or more over the advisory speed, with decreases up 41.1 percent noted. Large reductions resulted in the fraction of vehicles traveling 20 mph or more over the advisory speed, with a 27.1 percent reduction at 1 month, a 54.2 percent reduction at 12 months, and a 44.9 percent reduction at 24 months.
Table 83. Results for Ohio: Alkire Road at the PC (EB).
Before 
1 Mo 
Change 
12 Mo 
Change 
24 Mo 
Change 


Sample size 
2,913 
1,482 
NA 
1,488 
NA 
2,927 
NA 
Mean speed (mph) 
43.5 
43 
0.5 
40.7 
2.8 
41.1 
2.4 
SD of mean 
5.7 
5.1 
NA 
5.6 
NA 
6.2 
NA 
85th percentile speed (mph) 
49 
48 
1 
46 
3 
47 
2 
Fraction of vehicles exceeding posted or advisory speed limit 

By 5 mph 
0.95 
0.95 
0.2% 
0.87 
7.9% 
0.89 
6.6% 
By 10 mph 
0.81 
0.79 
2.4% 
0.60 
25.1% 
0.65 
19.6% 
By 15 mph 
0.43 
0.38 
11.9% 
0.25 
41.1% 
0.26 
38.3% 
By 20 mph 
0.12 
0.09 
27.1% 
0.05 
54.2% 
0.07 
44.9% 
NA = Not applicable
SD = Standard deviation
Table 84 provides results for the CC data collection location. Minor speed increases were noted for most of the speed metric for the 1month after period. Speeds had increased significantly at the upstream control point, which may suggest that the sign may have been more effective than shown in the results for the PC and CC.
Table 84. Results for Ohio: Alkire Road at the CC (EB).
Before 
1 Mo 
Change 
12 Mo 
Change 
24 Mo 
Change 


Sample size 
2,927 
3,006 
1,480 

2,906 


Mean speed (mph) 
41.5 
41.9 
0.4 
38.6 
2.9 
37.6 
3.9 
SD of mean 
6.1 
5.6 
5.6 

6.0 


85th percentile speed (mph) 
47 
47 
0 
44 
3 
43 
4 
Fraction of vehicles exceeding posted or advisory speed limit 

By 5 mph 
0.90 
0.93 
3.0% 
0.78 
13.4% 
0.73 
19.0% 
By 10 mph 
0.65 
0.70 
6.6% 
0.42 
35.4% 
0.37 
43.1% 
By 15 mph 
0.28 
0.31 
14.2% 
0.14 
49.1% 
0.10 
63.6% 
By 20 mph 
0.08 
0.07 
21.4% 
0.02 
71.4% 
0.02 
73.8% 
NA = Not applicable
SD = Standard deviation
Speeds decreased moderately at the 12 and 24month after periods, with decreases of 2.9 and 3.9 mph, and decreases of 3 and 4 mph in 85th percentile speeds. Large decreases occurred in the fraction of vehicles exceeding the advisory speed of 30 mph at the 12 and 24month after periods. Minor increases in the fraction of vehicles traveling 5, 10, or 15 mph or more over the advisory speed for the 1month after period (up to 14 percent) while a 21percent decrease occurred for vehicles traveling 20 mph or more over the advisory speed. At the 12 and 24month after periods, reductions occurred for all thresholds. The fraction of vehicles traveling 5 mph or more over decreased by up to 19 percent, the fraction traveling 10 mph or more decreased by up to 64 percent, and the percent traveling 20 mph or more over decreased by 74 percent.
Norton Road in Ohio was selected for a dynamic curve sign. The site has a posted speed limit of 55 mph and an advisory speed of 35 mph, and is located about 15 miles southwest of Columbus, OH. The sign was placed for the SB direction of traffic.
Table 85 shows results for the upstream speed control location. Minor speed decreases occurred at the upstream control sight. However, only the decrease in percent of vehicles traveling 5 mph or more over the posted speed limit was statistically significant. This suggests that no change in speeds occurred overall due to factors other than the dynamic curve sign.
Table 85. Results for Ohio: Norton Road upstream of curve (SB).
Before 
1 Mo 
Change 
12 Mo 
Change 
24 Mo 
Change 


ADT 
3,671 
3,382 
289 
3,496 
175 
3,255 
416 
Sample size 
7,192 
3,312 
NA 
6,849 
0.6 
6,266 
NA 
Mean speed (mph) 
50.0 
49.8 
0.2* 
50.6 
0.6 
49.7 
0.3 
SD of mean 
6.4 
6.3 
NA 
6.2 
NA 
6.3 
NA 
85th percentile speed (mph) 
56 
56 
0 
57 
1 
56 
0 
Fraction of vehicles exceeding posted or advisory speed limit 

By 5 mph 
0.05 
0.04 
25% 
0.06 
22% 
0.04 
45% 
By 10 mph 
0.01 
0.01 
25%* 
0.01 
8% 
0.01 
20% 
By 15 mph 
0.00 
0.00 
25%* 
0.00 
50%* 
0.00 
5%* 
By 20 mph 
0.00 
0.00 
0%* 
0.00 
0%* 
0.00 
5% 
*Not statistically significant
ADT = Average daily traffic
NA = Not applicable
SD = Standard deviation
Minor decreases were noted for the PC as shown in table 86. No real change in mean or 85th percentile speed occurred at 1 month. However, a moderate reduction in the percent of vehicles traveling 10, 15, or 20 mph over the advisory speed of 35 mph was noted (7.5, 9.0, and 2.2 percent).
Moderate decreases in mean speed (2.4 mph) and 85th percentile speed (2 mph) resulted for the 12month after period. Moderate decreases also resulted in the percent 5, 10, 15, and 20 mph over the advisory speed for the 12month after period. Minor increases resulted for the 24month after period, but most were not statistically significant.
Table 87 shows results for the CC data collection location. Moderate decreases were noted for all speed metrics with reductions of about 3 mph in mean and 85th percentile speeds at 1 month after installation of the signs. Significant decreases in the fraction of vehicles traveling over the advisory speed also occurred, with a 14percent decrease for 5 mph over, 41 percent decrease for 10 mph over, 64 percent decrease for 15 mph over, and 74 percent decrease for 20 mph over. Only minor changes occurred at the 12month after period, and increases occurred for the 24month after period.
Table 86. Results for Ohio: Norton Road at the PC (SB).
Before 
1 Mo 
Change 
12 Mo 
Change 
24 Mo 
Change 


Sample size 
7,005 
6,453 
NA 
3,819 
240 
6,247 
NA 
Mean speed (mph) 
50.1 
49.2 
0.9 
47.7 
2.4 
50.7 
0.6 
SD of mean 
5.6 
5.8 
NA 
5.3 
NA 
5.4 
NA 
85th percentile speed (mph) 
55 
55 
0 
53 
2 
56 
1 
Fraction of vehicles exceeding posted or advisory speed limit 

By 5 mph 
0.99 
0.96 
1.5% 
0.94 
3.6% 
0.98 
0.0%* 
By 10 mph 
0.89 
0.81 
8.5% 
0.74 
16.7% 
0.89 
0.2%* 
By 15 mph 
0.58 
0.49 
15.6% 
0.37 
36.0% 
0.62 
6.6% 
By 20 mph 
0.19 
0.16 
11.8% 
0.08 
54.8% 
0.23 
22.0% 
*Not statistically significant at 95percent level of significance
NA = Not applicable
SD = Standard deviation
Table 87. Results for Ohio: Norton Road at the CC (SB).
Before 
1 Mo 
Change 
12 Mo 
Change 
24 Mo 
Change 


Sample size 
7,037 
6,500 
NA 
7,441 
NA 
3,122 
NA 
Mean speed (mph) 
45.5 
42.4 
3.1 
45.3 
0.2 
47.5 
2.0 
SD of mean 
6.4 
6.1 
NA 
6.1 
NA 
6.0 
NA 
85th percentile speed (mph) 
51 
48 
3 
51 
0 
53 
2 
Fraction of vehicles exceeding posted or advisory speed limit 

By 5 mph 
0.88 
0.76 
14.4% 
0.88 
0.9% 
0.93 
5.2% 
By 10 mph 
0.65 
0.38 
41.3% 
0.60 
8.4% 
0.77 
18.5% 
By 15 mph 
0.23 
0.08 
63.9% 
0.22 
3.9% 
0.37 
60.5% 
By 20 mph 
0.04 
0.01 
73.7% 
0.04 
7.9% 
0.08 
110.5% 
NA = Not applicable
SD = Standard deviation
A dynamic curve sign was installed on Pontius Road in Ohio. The posted speed limit is 55 mph, and an advisory speed of 30 mph is present. The site is located about 15 miles southeast of Columbus, OH. Table 88 shows results for the upstream location (speed control).
Table 88. Results for Ohio: Pontius Road upstream of curve (SB).
Before 
1 Mo 
Change 
12 Mo 
Change 
24 Mo 
Change 


Sample size 
1,306 
1,213 
93 
1,233 
73 
1,100 
206 
Mean speed (mph) 
2,579 
2,404 
NA 
2,453 
NA 
978 
NA 
SD of mean 
52.5 
52.7 
0.2* 
49.1 
3.4 
50.3 
2.2 
85th percentile speed (mph) 
6.1 
5.5 
NA 
4.7 
NA 
5.2 
NA 
Sample size 
58 
58 
0 
53 
5 
55 
3 
Fraction of vehicles exceeding posted or advisory speed limit 

By 5 mph 
0.09 
0.09 
2.2%* 
0.01 
88.9% 
0.04 
58.9% 
By 10 mph 
0.02 
0.01 
17.6%* 
0.00 
88.2% 
0.00 
82.4% 
By 15 mph 
0.00 
0.00 
50.0%* 
0.00 
75.0% 
0.00 
75.0% 
By 20 mph 
0.00 
0.00 
0.0%* 
0.00 
0.0%* 
0.0 
0.0%* 
*Not statistically significant at 95percent level of significance
NA = Not applicable
SD = Standard deviation
Speed decreased or increased by very minor amounts for all speed metrics, but none of the changes were statistically significant at the 95percent level of significance. Speeds decreased moderately for the 12 and 24month after periods.
Changes in speed are noted in table 89 for the PC. Only minor changes occurred for change in mean speed (0.9 mph) and change in percent of vehicles exceeding the advisory speed of 30 mph by 5 mph or more (1 percent) at 1 month. Moderate increases in the percent of vehicles traveling 10, 15, or 20 mph or more over the advisory speed occurred.
Only minor changes occurred for the 12month after period, with most of the changes not being statistically significant. At the 24month after period, speeds were lower than for any of the previous time periods. Speed decreases were moderate, with a mean speed and 85th percentile decrease of 2 mph. Moderate decreases in the percent of vehicles exceeding the advisory speed by 5, 10, 15, or 20 mph occurred.
Fairly large increases in speed were noted in the CC data as shown in table 90 at 1 month. Mean speed increased by 2.8 mph, and the 85th percentile increased by 6 mph. There was also a large increase in the number of vehicles exceeding the advisory speed of 30 mph by 20 mph or more (211 percent). It is not likely that the presence of the sign caused the increase, but the reason for the increase is unknown.
Table 89. Results for Ohio: Pontius Road at the PC (SB).
Before 
1 Mo 
Change 
12 Mo 
Change 
24 Mo 
Change 


Sample size 
2,538 
2,499 
2,436 

2269 


Mean speed (mph) 
44.9 
45.8 
0.9 
45.0 
0.1 
43.0 
1.9 
SD of mean 
5.1 
4.8 
4.9 

5.8 


85th percentile speed (mph) 
50 
50 
0 
50 
0 
48 
2 
Fraction of vehicles exceeding posted or advisory speed limit 

By 5 mph 
0.97 
0.98 
0.9% 
0.98 
1.1% 
0.94 
3.1% 
By 10 mph 
0.88 
0.92 
4.0% 
0.88 
0.2%* 
0.75 
15.0% 
By 15 mph 
0.57 
0.64 
11.4% 
0.55 
4.0%* 
0.41 
28.7% 
By 20 mph 
0.15 
0.20 
34.2% 
0.16 
3.3%* 
0.11 
25.0% 
*Not statistically significant at 95percent level of significance
NA = Not applicable
SD = Standard deviation
Table 90. Results for Ohio: Pontius Road at the CC (SB).
Before 
1 Mo 
Change 
12 Mo 
Change 
24 Mo 
Change 


Sample size 
1,324 
1,856 
2,448 

2,271 


Mean speed (mph) 
44.4 
47.2 
2.8 
42.4 
2.0 
42.6 
1.8 
SD of mean 
4.7 
7.7 
5.0 

5.3 


85th percentile speed (mph) 
49 
55 
6 
47 
2 
47 
2 
Fraction of vehicles exceeding posted or advisory speed limit 

By 5 mph 
0.97 
0.97 
0.5%* 
0.95 
2.2% 
0.96 
1.8% 
By 10 mph 
0.87 
0.86 
1.0%* 
0.73 
16.2% 
0.75 
13.6% 
By 15 mph 
0.51 
0.62 
22.0% 
0.34 
33.8% 
0.34 
32.8% 
By 20 mph 
0.12 
0.38 
210.7% 
0.06 
48.4% 
0.07 
40.2% 
*Not statistically significant at 95percent level of significance
NA = Not applicable
SD = Standard deviation
Speeds at the PC and upstream location were nearly unchanged from the before period to the 1month after period, suggesting that speeds overall did not increase. A check of the traffic counting equipment and data did not reveal any equipment malfunction. Moderate speed decreases occurred at the 12 and 24month after periods, with decreases of about 2 mph for the mean and 85th percentile speeds for both periods. Moderate decreases occurred in the fraction of vehicles exceeding the advisory speed.
The treatment site on OR 42 in Oregon has a posted speed limit of 55 mph and an advisory speed of 35 mph. The sign type is a dynamic speed sign. The site is located 34 miles southwest of Roseburg, OR. The curve advisory speed is 35 mph, and the tangent speed is 55 mph. The sign was installed in October 2009. Data were collected through the 12month after period. The sign experienced a large number of maintenance issues; after numerous fixes were attempted, it was determined that continued maintenance was beyond project resources, and the sign was removed in September 2011.
Table 91 shows results for the upstream location (speed control). At 1 month after, minor decreases in speed resulted for all speed metrics. Although only minor actual decreases resulted, the percent change in the fraction of vehicles exceeding the advisory speed was fairly significant. At 12 months, essentially no speed changes had occurred.
Table 91. Results for Oregon: OR 42 upstream of curve (WB).
Before 
1 Mo 
Change 
12 Mo 
Change 


ADT 
1,119 
1,112 
7 
1,146 
27 
Sample size 
2,081 
2,082 
NA 
2,292 
NA 
Mean speed (mph) 
60.7 
59.5 
1.2 
60.1 
0.6 
SD of mean 
5.7 
5.2 
NA 
6.5 
NA 
85th percentile speed (mph) 
66 
64 
2 
66 
0 
Fraction of vehicles exceeding posted or advisory speed limit 

By 5 mph 
0.59 
0.48 
19.4% 
0.54 
9.3% 
By 10 mph 
0.22 
0.14 
36.5% 
0.21 
3.7% 
By 15 mph 
0.06 
0.03 
58.1% 
0.05 
12.9% 
By 20 mph 
0.02 
0.01 
61.5% 
0.02 
23.1% 
ADT = Average daily traffic
NA = Not applicable
SD = Standard deviation
Table 92 provides results for the PC. A significant decrease of 4 mph in mean and 85th percentile speed occurred at the 1month after period, with a 6 mph decrease in both metrics for the 12month after period. Moderate decreases occurred for vehicles traveling 5 mph or more over the advisory speed (6 percent for the 1month after period, and 13 percent for the 12month after period).
Significant decreases resulted for the percent of vehicles traveling 10, 15, 20 mph or more over the advisory speed limit of 35 mph, with decreases of 19.9 percent and 32.2 percent for 10 mph or more over, 40.2 percent and 61.6 percent for 15 mph or more over, and 64.5 percent and 81.1 percent for 20 mph or more over.
Table 92. Results for Oregon: OR 42 at the PC (WB).
Before 
1 Mo 
Change 
12 Mo 
Change 


ADT 
1,022 
1,112 
90 
1,237 
215 
Sample size 
1,809 
2,090 
NA 
2,270 
NA 
Mean speed (mph) 
51.8 
47.7 
4.1 
45.7 
6.1 
SD of mean 
6.3 
6.2 
NA 
6.1 
NA 
85th percentile speed (mph) 
58 
54 
4 
52 
6 
Fraction of vehicles exceeding posted or advisory speed limit 

By 5 mph 
0.97 
0.91 
6.1% 
0.85 
12.5% 
By 10 mph 
0.89 
0.71 
19.9% 
0.60 
32.2% 
By 15 mph 
0.67 
0.40 
40.2% 
0.26 
61.6% 
By 20 mph 
0.34 
0.12 
64.5% 
0.06 
81.1% 
ADT = Average daily traffic
NA = Not applicable
SD = Standard deviation
Table 93 shows results for the CC on OR 42. A decrease of about 3 mph was noted for the mean and 85th percentile speeds at 1 month, and 2.3 and 3 mph at 12 months. Reductions in the percent of vehicles traveling over the advisory speed limit were also recorded that were greater in most cases than at the PC.
Table 93. Results for Oregon: OR 42 at the CC (WB).
Before 
1 Mo 
Change 
12 Mo 
Change 


ADT 
1,113 
1,366 
253 
1,385 
272 
Sample size 
2,066 
2,178 
NA 
2,361 
NA 
Mean speed 
43.1 
40.4 
2.7 
40.8 
2.3 
SD of mean 
5.0 
4.7 
NA 
5.4 
NA 
85th percentile speed 
49 
46 
3 
46 
3 
Fraction of vehicles exceeding posted or advisory speed limit 

by 5 mph 
0.76 
0.58 
23.6% 
0.61 
20.7% 
by 10 mph 
0.40 
0.22 
44.3% 
0.23 
42.5% 
by 15 mph 
0.10 
0.04 
54.7% 
0.05 
52.6% 
by 20 mph 
0.01 
0.01 
46.2% 
0.01 
15.4%* 
*Not statistically significant at 95percent level of significance
ADT = Average daily traffic
NA = Not applicable
SD = Standard deviation
A dynamic speed sign was selected for the treatment site on OR 238 in Oregon. The posted speed limit is 55 mph with an advisory speed of 30 mph. The sign was placed for the EB direction of traffic. The sign was installed in October 2009, and the site is 12 miles southeast of Grants Pass, OR. Table 94 shows results for the upstream speed control location.
Table 94. Results for Oregon: OR 238 upstream of curve (EB).
Before 
1 Mo 
Change 
12 Mo 
Change 
24 Mo 
Change 


ADT 
1,719 
1,585 
134 
1,767 
48 
1,759 
40 
Sample size 
3,404 
3,136 
NA 
1,731 
NA 
3457 
NA 
Mean speed (mph) 
53.3 
53.4 
0.1* 
52.5 
0.8 
53.5 
0.2* 
SD of mean 
5.0 
5.6 
NA 
5.6 
NA 
5.5 
NA 
85th percentile speed (mph) 
58 
59 
1 
58 
0 
58 
0 
Fraction of vehicles exceeding posted or advisory speed limit 

By 5 mph 
0.09 
0.12 
30.0% 
0.09 
5.6%* 
0.11 
20.0% 
By 10 mph 
0.02 
0.02 
5.3%* 
0.02 
10.5%* 
0.02 
15.8%* 
By 15 mph 
0.00 
0.00 
50.0%* 
0.01 
25.0%* 
0.00 
25.0%* 
By 20 mph 
0.00 
0.00 
0.0%* 
0.00 
0.0%* 
0.00 
0.0%* 
*Not statistically significant at 95percent level of significance
ADT = Average daily traffic
NA = Not applicable
SD = Standard deviation
Small increases in speeds were noted at the upstream control site, although most of the differences were not statistically significant. This indicates that no major changes in speed occurred at the control data collection location.
Moderate decreases in mean and 85th percentile (about 3 mph) were found at the PC for OR 238, as shown in table 95, for both the 1month and 12month after periods. More significant changes in the percent of vehicles exceeding the advisory curve speed of 30 mph occurred, as shown.
There was a decrease of up to 17 percent in the fraction of vehicles exceeding the advisory speed by 5 mph, a decrease up to 42 percent in vehicles exceeding the advisory speed by 10 mph, a decrease up to 61 percent for vehicles exceeding the advisory speed by 15 mph, and a decrease up to 72 percent in vehicles exceeding the advisory speed by 20 mph.
Table 95. Results for Oregon: OR 238 at the PC (EB).
Before 
1 Mo 
Change 
12 Mo 
Change 
24 Mo 
Change 


Sample size 
3,338 
3,119 
NA 
3,440 
NA 
3,371 
NA 
Mean speed (mph) 
41.7 
38.3 
3.4 
38.9 
2.8 
39.6 
2.1 
SD of mean 
4.4 
5.0 
NA 
4.6 
NA 
4.9 
NA 
85th percentile speed (mph) 
46 
43 
3 
43 
3 
44 
2 
Fraction of vehicles exceeding posted or advisory speed limit 

By 5 mph 
0.95 
0.79 
16.7% 
0.84 
11.8% 
0.86 
9.1% 
By 10 mph 
0.71 
0.41 
42.1% 
0.46 
35.4% 
0.52 
27.1% 
By 15 mph 
0.25 
0.10 
61.0% 
0.10 
59.4% 
0.15 
40.6% 
By 20 mph 
0.03 
0.01 
62.1% 
0.01 
72.4% 
0.02 
34.5% 
NA = Not applicable
SD = Standard deviation
Although reductions were smaller, similar results were found for the CC as for the PC as shown in table 96.
Table 96. Results for Oregon: OR 238 at the CC (EB)
Before 
1 Mo 
Change 
12 Mo 
Change 
24 Mo 
Change 


ADT 
1,696 
1,535 
161 
1,965 
269 
1,751 
55 
Sample size 
3,331 
3,027 
NA 
3,302 
NA 
1704 
NA 
Mean speed (mph) 
36.8 
34.3 
2.5 
36.4 
0.4 
35.7 
1.1 
SD of mean 
4.0 
3.9 
NA 
4.1 
NA 
3.9 
NA 
85th percentile speed (mph) 
41 
38 
3 
40 
1 
39 
2 
Fraction of vehicles exceeding posted or advisory speed limit 

By 5 mph 
0.73 
0.48 
34.0% 
0.69 
6.2% 
0.62 
14.5% 
By 10 mph 
0.23 
0.09 
62.6% 
0.21 
10.0% 
0.15 
36.5% 
By 15 mph 
0.03 
0.01 
77.8% 
0.02 
18.5%* 
0.02 
40.7% 
By 20 mph 
0.00 
0.00 
50.0% 
0.00 
0.0%* 
0.00 
50.0%* 
*Not statistically significant at 95percent level of significance
NA = Not applicable
SD = Standard deviation
The mean and 85th percentile speeds decreased by up to 3 mph, and large decreases in the percent of vehicles exceeding the advisory speed by 5 (34 percent), 10 mph (63 percent), 15 mph (78 percent), and 20 mph (50 percent) occurred for the 1month after period. Decreases at the 12month after period were minor, and changes in the percent over the number of vehicles exceeding the advisory speed by 15 and 20 mph were not statistically significant. Changes at 24 months were higher than for the 12month after period, with a decrease in mean speed of 1.1 mph and 2 mph for 85th percentile speeds. Small decreases resulted for the changes in vehicles traveling over the advisory speed.
US 101 in Oregon was selected for a dynamic curve sign. The posted speed limit is 55 mph with an advisory speed of 45 mph. The sign was placed for the SB direction of traffic. Speed and volume data were collected through the 1month after period. The sign had numerous problems, including power issues, problems with LEDs, etc. The sign was fixed several times, and fixing the sign required a longdistance trip each time. The sign quit functioning again after the 12month after period. As a result, after 12 months, it was decided to abandon further fixes to the sign, so 24month after data were not collected.
Table 97 shows results for the upstream speed control data collection location. Moderate increases in speeds were noted at the upstream control site for most of the speed metrics except for the percent of vehicles traveling 15 or 20 mph or more over the posted speed limit.
Table 97. Results for Oregon: US 101 upstream of curve (SB).
Before 
1 Mo 
Change 
12 Mo 
Change 


ADT 
1,410 
1,468 
58 
1,934 
524 

Sample size 
2,746 
2,788 
NA 
3,758 
NA 

Mean speed (mph) 
52.6 
55.1 
2.5 
60.2 
7.6 

SD of mean 
5.6 
6.7 
NA 
6.6 
NA 

85th percentile speed (mph) 
58 
61 
3 
67 
9 

Fraction of vehicles exceeding posted or advisory speed limit 

By 5 mph 
0.09 
0.21 
120% 
0.57 
504% 

By 10 mph 
0.01 
0.04 
157% 
0.25 
1,714% 

By 15 mph 
0.00 
0.00 
50%* 
0.07 
3,250% 

By 20 mph 
0.00 
0.00 
0%* 
0.02 
0% 
*Not statistically significant at 95percent level of significance
ADT = Average daily traffic
NA = Not applicable
SD = Standard deviation
Significant increases resulted for the 12month after period, with an increase in mean speed of 7.6 mph and an increase in 85th percentile speed of 9 mph. Significant increases also resulted for the fraction of vehicles traveling over the speed limit.
Table 98 presents results for the PC. Minor decreases in mean (0.8 mph) and 85th percentile speed (1 mph) were reported at 1 month. Modest decreases in the percent of vehicles traveling over the advisory speed of 45 mph were noted. Similar decreases for mean (1.8 mph) and 1 mph in 85th percentile speed occurred.
Moderate decreases occurred after 12 months that were even greater than after 1 month for the percent over the advisory speed, with up to a 10percent decrease in the fraction of vehicles traveling 5 mph or more over the advisory speed. Decreases up to 26.2 percent occurred for vehicles traveling 10 mph or more over the advisory speed while a 35 percent reduction occurred for vehicles traveling 15 mph or more over. Decreases up to 53.5 percent in the fraction of vehicles traveling 20 mph or more over were noted. Because speeds increased at the control site, the effectiveness of the signs may be even greater than noted.
Table 98. Results for Oregon: US 101 at the PC (SB).
Before 
1 Mo 
Change 
12 Mo 
Change 


Sample size 
2,769 
2,823 
NA 
3,796 
NA 
Mean speed (mph) 
55.6 
54.8 
0.8 
53.8 
1.8 
SD of mean 
6.7 
5.2 
NA 
6.5 
NA 
85th percentile speed (mph) 
61 
60 
1 
60 
1 
Fraction of vehicles exceeding posted or advisory speed limit 

By 5 mph 
0.88 
0.86 
2.3% 
0.79 
10.7% 
By 10 mph 
0.65 
0.55 
15.0% 
0.48 
26.2% 
By 15 mph 
0.26 
0.17 
34.6% 
0.17 
35.8% 
By 20 mph 
0.04 
0.02 
53.5% 
0.03 
30.2% 
NA = Not applicable
SD = Standard deviation
A significant decrease in mean and 85th percentile speeds (almost 6 mph) occurred at the CC, as shown in table 99, for both the 1 and 12month after periods. Very large decreases in vehicles traveling at high speeds resulted with a reduction of 43.0 percent of vehicles traveling 5 mph or more and up to 78.7 percent reduction in vehicles traveling 10 mph or more over the advisory speed of 45 mph. Reductions up to 95.3 percent were observed in the fraction of vehicles traveling 15 mph or more over the advisory speed and up to 96.7 percent reduction for vehicles traveling 20 mph or more over.
Table 99. Results for Oregon: US 101 at the CC (SB).
Before 
1 Mo 
Change 
12 Mo 
Change 


ADT 
1,418 
1,369 
49 
1,963 
545 
Sample size 
2,770 
1,343 
NA 
3,821 
NA 
Mean speed (mph) 
54.8 
49.2 
5.6 
49.2 
5.6 
SD of mean 
5.5 
4.6 
NA 
5.7 
NA 
85th percentile speed (mph) 
60 
54 
6 
55 
5 
Fraction of vehicles exceeding posted or advisory speed limit 

By 5 mph 
0.85 
0.48 
43.0% 
0.50 
41.4% 
By 10 mph 
0.54 
0.11 
78.7% 
0.17 
67.7% 
By 15 mph 
0.19 
0.01 
95.3% 
0.03 
86.0% 
By 20 mph 
0.03 
0.00 
96.7% 
0.00 
93.3% 
ADT = Average daily traffic
NA = Not applicable
SD = Standard deviation
OR 126 in Oregon has a posted speed limit of 55 mph with no advisory speed. A dynamic curve sign was placed for the EB direction of traffic. The site is 24 miles west of Eugene, OR. The sign was installed in January 2010.
Table 100 shows results for the upstream speed control data collection location. As shown, moderate decreases in speeds occurred at the upstream control site for all of the speed metrics after 1 month and significant decreases occurred at the 12month after period, with decreases of 4.7 mph in average speed and 6 mph for the 85th percentile speed.
Table 100. Results for Oregon: OR 126 upstream of curve (EB).
Before 
1 Mo 
Change 
12 Mo 
Change 
24 Mo 
Change 


ADT 
1,878 
1,822 
56 
2,191 
313 
2,126 
248 
Sample size 
3,677 
3,549 
4,279 

4,119 


Mean speed (mph) 
56.9 
55.2 
1.7 
55.8 
1.1 
52.2 
4.7 
SD of mean 
6.0 
5.7 
6.0 

5.6 


85th percentile speed (mph) 
63 
61 
2 
61 
2 
57 
6 
Fraction of vehicles exceeding posted or advisory speed limit 

By 5 mph 
0.31 
0.21 
31.5% 
0.24 
23.5% 
0.09 
72.7% 
By 10 mph 
0.10 
0.05 
52.1% 
0.06 
33.3% 
0.01 
85.4% 
By 15 mph 
0.02 
0.01 
59.1% 
0.01 
36.4% 
0.00 
90.9% 
By 20 mph 
0.01 
0.00 
60.0% 
0.00 
20.0%* 
0.0 
100.0% 
*Not statistically significant at 95percent level of significance
ADT = Average daily traffic
NA = Not applicable
SD = Standard deviation
Table 101 shows results for the PC. Minor decreases occurred for all speed metrics for all of the after periods, although the decreases were smaller than for the control point. This may suggest that the sign had limited effectiveness for the PC.
Decreases were the greatest for the 24month after period, with a decrease of almost 2 mph in mean speed and 1 mph in 85th percentile speed. A 6.5 percent decrease resulted for the number of vehicles traveling 5 mph over the advisory speed, with an 18.0percent decrease in the fraction of vehicles traveling 10 mph or more over, 23.4percent decrease for 15 mph over, and 14.4percent decrease for vehicles traveling 20 or mph over.
Table 101. Results for Oregon: OR 126 at the PC (EB).
Before 
1 Mo 
Change 
12 Mo 
Change 
24 Mo 
Change 


Sample size 
3,648 
3,545 
NA 
4,233 
NA 
4,123 
NA 
Mean speed (mph) 
53.7 
53.1 
0.6 
53.5 
0.2* 
52.0 
1.7 
SD of mean 
5.3 
5.9 
NA 
6.5 
NA 
6.0 
NA 
85th percentile speed (mph) 
59 
59 
0 
60 
1 
58 
1 
Fraction of vehicles exceeding posted or advisory speed limit 

By 5 mph 
0.96 
0.94 
1.5% 
0.92 
3.3% 
0.89 
6.5% 
By 10 mph 
0.81 
0.73 
9.9% 
0.73 
10.2% 
0.67 
18.0% 
By 15 mph 
0.44 
0.39 
11.6% 
0.44 
0.5%* 
0.34 
23.4% 
By 20 mph 
0.12 
0.13 
9.3%* 
0.17 
44.9% 
0.10 
14.4% 
*Not statistically significant at 95percent level of significance
NA = Not applicable
SD = Standard deviation
Table 102 shows results for the CC for OR 126. Minor decreases also occurred for all speed metrics for the 1month and 24month after periods. Decreases are greater in most cases than for the control site. A fairly substantial decrease in the percent of vehicles traveling over the posted speed limit by 15 and 20 mph was noted.
Table 102. Results for Oregon: OR 126 at the CC (EB).
Before 
1 Mo 
Change 
12 Mo 
Change 
24 Mo 
Change 


Sample size 
3,729 
3,563 
NA 
4,260 
NA 
4,108 
NA 
Mean speed (mph) 
50.9 
49.6 
1.3 
46.5 
4.4 
48.8 
2.1 
SD of mean 
5.7 
5.2 
NA 
5.4 
NA 
5.7 
NA 
85th percentile speed (mph) 
56 
55 
1 
52 
4 
55 
1 
Fraction of vehicles exceeding posted or advisory speed limit 

By 5 mph 
0.88 
0.85 
3.5% 
0.65 
26.5% 
0.78 
12.0% 
By 10 mph 
0.60 
0.48 
19.4% 
0.27 
54.9% 
0.43 
28.5% 
By 15 mph 
0.24 
0.16 
32.5% 
0.07 
72.4% 
0.16 
35.4% 
By 20 mph 
0.06 
0.03 
46.8% 
0.01 
87.1% 
0.04 
40.3% 
NA = Not applicable
SD = Standard deviation
Moderate decreases in mean (4.4 mph) and 85th percentile speeds (4 mph) resulted for the 24month after period. Moderate decreases also resulted for the fraction traveling over the advisory speed, with up to 26.5 percent decrease for the 5 mph over, up to 54.9 percent decrease for 10 mph or more over, up to 72.5 percent decrease for the 15 mph over, and up to 87.1 percent for 20 mph over.
A speed display sign was installed at Texas site FM 481 in April 2010. The site has a curve advisory speed of 50 mph and a speed limit of 65 mph for passenger vehicles. The speed limit for trucks is 60 mph during the daytime and 55 mph at nighttime. The site is 20 miles southwest of Uvalde, TX.
Results are summarized below. Table 103 shows speed and volume changes for the upstream control section. Moderate speed increases resulted for all the after periods for all speed metrics.
Table 103. Results for Texas: FM 481 upstream of curve (EB).
Before 
1 Mo 
Change 
12 Mo 
Change 
24 Mo 
Change 


ADT 
523 
545 
22 
442 
81 
473 
50 
Sample size 
975 
957 
NA 
865 
NA 
466 
NA 
Mean speed (mph) 
65.9 
68.2 
2.3 
68.5 
2.6 
67.5 
1.6 
SD of mean 
6.7 
7.1 
NA 
6.9 
NA 
6.6 
NA 
85th percentile speed (mph) 
72 
74 
2 
77 
5 
67 
2 
Fraction of vehicles exceeding posted or advisory speed limit 

By 5 mph 
0.24 
0.40 
63.1% 
0.42 
73.8% 
0.35 
43.4% 
By 10 mph 
0.08 
0.14 
75.6% 
0.14 
74.4% 
0.12 
51.2% 
By 15 mph 
0.02 
0.06 
137.5% 
0.05 
125.0% 
0.04 
70.8% 
By 20 mph 
0.01 
0.03 
333.3% 
0.02 
283.3% 
0.02 
150.0% 
ADT = Average daily traffic
NA = Not applicable
SD = Standard deviation
Table 104 shows results for FM 481 at the PC. Significant decreases occurred in mean and 85th percentile speeds for the 1, 12, and 24month after periods (between 4 and 6 mph). Decreases up to 16.5 percent in the fraction of vehicles traveling 5 mph or more over the advisory speed resulted, and decreases up to 35.2 percent in vehicles traveling 10 mph or more over.
Table 104. Results for Texas: FM 481 at the PC (EB).
Before 
1 Mo 
Change 
12 Mo 
Change 
24 Mo 
Change 


Sample size 
993 
982 
NA 
876 
NA 
463 
NA 
Mean speed (mph) 
66.7 
61.5 
5.2 
61.1 
5.6 
61.0 
5.7 
SD of mean 
7 
7.7 
NA 
7.7 
NA 
7.2 
NA 
85th percentile speed (mph) 
73 
69 
4 
69 
4 
68 
5 
Fraction of vehicles exceeding posted or advisory speed limit 

By 5 mph 
0.96 
0.82 
14.1% 
0. 08 
16.5% 
0.81 
14.9% 
By 10 mph 
0.86 
0.62 
28.5% 
0.60 
29.8% 
0.56 
35.2% 
By 15 mph 
0.66 
0.38 
42.3% 
0.35 
47.3% 
0.33 
49.9% 
By 20 mph 
0.36 
0.03 
91.3% 
0.11 
70.1% 
0.11 
67.9% 
NA = Not applicable
SD = Standard deviation
A significant decrease in vehicles traveling 15 mph or more resulted with decreases between 42.3 and 49.9 2 percent. A large reduction in vehicles traveling 20 mph or more over the advisory speed resulted, with decreases of up to 91.3 percent.
Table 105 shows changes in speed metrics for the CC. Mean speed increased by approximately 1 mph and 85th percentile speed increased by 3 mph for the 1month after period. Many of the changes in percent of vehicles over the advisory speed were not statistically significant.
Table 105. Results for Texas: FM 481 at the CC (EB)
Before 
1 Mo 
Change 
12 Mo 
Change 
24 Mo 
Change 


Sample size 
998 
984 

854 

446 

Mean speed (mph) 
61.0 
62.3 
1.3 
60.1 
0.9 
60.0 
1.0 
SD of mean 
6.9 
7.8 

7.1 

7.0 

85th percentile speed (mph) 
67 
70 
3 
67 
0 
67 
0 
Fraction of vehicles exceeding posted or advisory speed limit 

By 5 mph 
0.87 
0.86 
1.8%* 
0.80 
7.7% 
0.81 
7.3% 
By 10 mph 
0.65 
0.64 
0.2%* 
0.55 
14.4% 
0.50 
21.9% 
By 15 mph 
0.29 
0.33 
13.1% 
0.25 
12.7% 
0.26 
12.0% 
By 20 mph 
0.06 
0.17 
160.9% 
0.07 
4.7%* 
0.07 
15.6% 
*Not statistically significant at 95percent level of significance
NA = Not applicable
SD = Standard deviation
At 12 and 24 months, mean speed decreased by about 1 mph with no change in the 85th percentile speed. A decrease of up to 7.7 percent resulted for vehicles traveling 5 mph or more over the advisory speed. A decrease of up to 21.9 percent resulted for vehicles traveling 10 mph or more over the advisory speed and a decrease up to 13.1 percent occurred for vehicles traveling 15 mph or more over the advisory speed. Increases were noted for vehicles traveling 20 mph or more over the advisory speed.
A dynamic speed sign was installed on FM 755 in Texas for the WB direction of traffic. The site is 39 miles northeast of Rio Grande City, TX. The site has a posted speed limit of 65 mph with a posted truck speed of 60 for daytime and 55 mph for nighttime. The sign was vandalized and knocked over right after installation so data were not collected for the 1month after period. Data were collected at 12 months. Results for the 12month after period are summarized below.
The sign was knocked over again before the 24month after period and was not functioning at the 24month after data collection period. Table 106 shows speed and volume the 12month after period for all speed metrics.
Table 106. Results for Texas: FM 755 upstream of curve (WB).
Before 
12 Mo 
Change 


ADT 
346 
399 
NA 
Sample size 
663 
781 
NA 
Mean speed (mph) 
66.9 
68.8 
1.9 
SD of mean 
8.8 
8.1 
NA 
85th percentile speed (mph) 
75 
76 
1 
Fraction of vehicles exceeding posted or advisory speed limit 

By 5 mph 
0.34 
0.42 
26.2% 
By 10 mph 
0.17 
0.20 
17.5%* 
By 15 mph 
0.07 
0.08 
15.5%* 
By 20 mph 
0.02 
0.04 
66.7%* 
*Not statistically significant at 95percent level of significance
ADT = Average daily traffic
NA = Not applicable
SD = Standard deviation
Moderate speed changes resulted for the PC as shown in table 107. Mean speed decreased by 2.9 mph and 85th percentile speed decreased by 4 mph. The fraction of vehicles traveling 5 mph or more over the posted speed limit decreased by 10.0 percent, and the fraction traveling 10 mph or more over decreased by 28.3 percent. A 35.6 percent decrease resulted for the fraction traveling 15 mph over. The fraction of vehicles traveling 20 mph or more over the advisory speed decreased by 68.5 percent.
Table 107. Results for Texas: FM 755 at the PC (WB).
Before 
12 Mo 
Change 


Sample size 
658 
319 
NA 
Mean speed (mph) 
62.7 
59.8 
2.9 
SD of mean 
8.5 
7.4 
NA 
85th percentile speed (mph) 
71 
67 
4 
Fraction of vehicles exceeding posted or advisory speed limit 

By 5 mph 
0.85 
0.76 
10.0% 
By 10 mph 
0.69 
0.50 
28.3% 
By 15 mph 
0.43 
0.28 
35.6% 
By 20 mph 
0.18 
0.06 
68.5% 
*Not statistically significant at 95percent level of significance
NA = Not applicable
SD = Standard deviation
Only moderate changes occurred at the CC for FM 755, as shown in table 108. A minor decrease of 1.4 mph in the average speed and an increase of 1 mph in the 85th percentile speed resulted. No statistically significant changes in vehicles traveling over the advisory speed occurred at the CC.
Table 108. Results for Texas: FM 755 at the CC (WB).
Before 
12 Mo 
Change 


Sample size 
656 
332 


Mean speed (mph) 
54.5 
55.9 
1.4 

SD of mean 
9.6 
7.5 


85th percentile speed (mph) 
63 
62 
1 

Fraction of vehicles exceeding posted or advisory speed limit 

By 5 mph 
0.58 
0.61 
4.0%* 

By 10 mph 
0.30 
0.30 
0.3%* 

By 15 mph 
0.10 
0.11 
10.5%* 

By 20 mph 
0.01 
0.02 
100.0%* 
*Not statistically significant at 95percent level of significance
NA = Not applicable
SD = Standard deviation
A curve advisory sign was installed on SH 359 in Texas in April 2010. The tangent speed is 70 mph with a truck speed that is 65 mph at night. The site is 45 miles west of Laredo, TX. The sign faces the WB direction of traffic.
Table 109 shows speed and volume changes for the upstream control section. Minor speed decreases resulted for the 1, 12, and 24month after periods for all speed metrics.
Table 109. Results for Texas: SH 359 upstream of curve (WB).
Before 
1 Mo 
Change 
12 Mo 
Change 
24 Mo 
Change 


ADT 
1,483 
1,596 
113 
1,408 
75 
1,570 
87 
Sample size 
2,889 
3,049 
NA 
2,692 
NA 
1485 
NA 
Mean speed (mph) 
67.6 
65.3 
2.3 
67.3 
0.3* 
66.8 
0.8 
SD of mean 
6.1 
5.5 
NA 
5.9 
NA 
5.7 
NA 
85th percentile speed (mph) 
73 
70 
3 
72 
1 
67 
2 
Fraction of vehicles exceeding posted or advisory speed limit 

By 5 mph 
0.10 
0.04 
64.6% 
0.08 
21.2% 
0.06 
37.4% 
By 10 mph 
0.04 
0.01 
64.9% 
0.02 
37.8% 
0.02 
48.6% 
By 15 mph 
0.01 
0.01 
58.3% 
0.01 
33.3%* 
0.01 
25.0% 
By 20 mph 
0.00 
0.00 
33.3%* 
0.00 
66.7% 
0.00 
0.0% 
* Not statistically significant at 95percent level of significance
ADT = Average daily traffic
NA = Not applicable
SD = Standard deviation
Table 110 shows results at the PC. Moderate speed decreases resulted for the 1 and 12month after periods for SH 359 at the PC of the curve. A decrease of 3.4 and 1.7 mph occurred for the 1 and 12month after periods, respectively, with decreases of 5 and 3 mph for 85th percentile speed.
Table 110. Results for Texas: SH 359 at the PC (WB).
Before 
1 Mo 
Change 
12 Mo 
Change 
24 Mo 
Change 


Sample size 
2,894 
3,048 
NA 
2,712 
NA 
1490 
NA 
Mean speed (mph) 
69.6 
66.2 
3.4 
67.9 
1.7 
67.7 
1.9 
SD of mean 
6.6 
5.5 
NA 
5.7 
NA 
5.7 
NA 
85th percentile speed (mph) 
75 
70 
5 
72 
3 
72 
3 
Fraction of vehicles exceeding posted or advisory speed limit 

By 5 mph 
0.17 
0.04 
75.0% 
0.08 
51.2% 
0.07 
57.1% 
By 10 mph 
0.06 
0.01 
80.0% 
0.02 
58.2% 
0.03 
54.5% 
By 15 mph 
0.02 
0.00 
78.9% 
0.01 
73.7% 
0.01 
47.4% 
By 20 mph 
0.01 
0.00 
50.0% 
0.00 
100.0% 
0.01 
16.7% 
NA = Not applicable
SD = Standard deviation
Because the speed limit was high (70 mph) with no advisory speed, only a moderate number of vehicles exceeded the posted speed limit in the before period for any of the speed intervals. Significant decreases in the fraction of vehicles exceeding the posted speed limit resulted (up to 75 percent for 5 mph or more, up to 80 percent for 10 mph or more, up to 79 percent for 15 mph or more and up to 100 percent for 20 mph or more).
Table 111 provides speed changes at the CC for SH 359. Moderate decreases in mean speed (2.3 mph) and 85th percentile speeds (3 mph) resulted for the 1month after period. Minor changes resulted for the fraction traveling over the posted speed limit, although the magnitude of change was significant.
Table 111. Results for Texas: SH 359 at the CC (WB).
Before 
1 Mo 
Change 
12 Mo 
Change 
24 Mo 
Change 


Sample size 
2,854 
3,043 
NA 
3,206 
NA 
67.2 
NA 
Mean speed (mph) 
69.6 
67.3 
2.3 
66.8 
2.8 
6.2 
2.4 
SD of mean 
6.5 
5.7 
NA 
6.9 
NA 
72 
NA 
85th percentile speed (mph) 
75 
72 
3 
72 
3 
67.2 
3 
Fraction of vehicles exceeding posted or advisory speed limit 

By 5 mph 
0.17 
0.06 
66.1% 
0.08 
55.0% 
0.06 
64.3% 
By 10 mph 
0.05 
0.02 
59.6% 
0.01 
72.3% 
0.02 
68.1% 
By 15 mph 
0.02 
0.01 
68.8% 
0.00 
87.5% 
0.01 
50.0% 
By 20 mph 
0.01 
0.00 
57.1% 
0.00 
85.7% 
0.00 
57.1% 
NA = Not applicable
SD = Standard deviation
At 12 months, speeds had increased, with a 3mph increase in both mean and 85th percentile speeds and minor increases in the fraction of vehicles exceeding the posted speed limit.
A curve advisory sign was placed on US 90 in Texas for the EB direction of traffic. The posted speed limit is 70 mph, and no advisory speed is present. The site is located 35 miles west of Uvalde, TX. The sign was installed in April 2010. The sign quit functioning in January 2011. It was decided that the cost was too prohibitive to make an additional trip to fix the sign. As a result, data were not collected for the 24month after period.
Results for the 12month after period are summarized below. Table 112 shows speed and volume changes for the upstream control section. Minor increases in mean and 85th percentile speeds resulted for both the 1month and 12month after periods and large increases in the percent of vehicles traveling 5, 10, or 15 mph or more over the posted speed limit.
Table 112. Results for Texas: US 90 upstream of curve (EB).
Before 
1 Mo 
Change 
12 Mo 
Change 

ADT 
1,525 
1,502 
NA 
1,549 
NA 
Sample size 
2,834 
2,908 
NA 
2,773 
NA 
Mean speed (mph) 
68.3 
69.1 
0.8 
69.1 
0.8 
SD of mean 
5.3 
5.4 
NA 
5.7 
NA 
85th percentile speed (mph) 
73 
73 
0 
74 
1 
Fraction of vehicles exceeding posted or advisory speed limit 

By 5 mph 
0.08 
0.10 
26.6% 
0.11 
34.2% 
By 10 mph 
0.01 
0.01 
40.0%* 
0.02 
50.0% 
By 15 mph 
> 0.00 
> 0.00 
200.0% 
> 0.00 
300.0% 
By 20 mph 
0.00 
0.00 
0.0% 
> 0.00 
0.0% 
*Not statistically significant at 95percent level of significance
ADT = Average daily traffic
NA = Not applicable
SD = Standard deviation
Table 113 shows results for the PC for US 90. Minor speed increases occurred for the 1month after period, although most of changes were in vehicles traveling over the posted speed limit. Minor and relatively insignificant changes occurred at 12 months at the PC. However, moderate increases had occurred at the upstream control location, so speeds may have increased overall, making the impact of the signs less obvious.
As shown in Table 114, moderate decreases resulted for the 1month and 12month after periods at the CC for US 90 (about 1 to 2 mph for both mean and 85th percentile speeds). Although decreases in percent of vehicles traveling over the posted speed limit resulted, most of the decreases were not statistically significant. However, speeds had increased at the control site, which may indicate speeds had increased overall. In addition, given the speed limit was so high, it may be difficult to detect changes.
Table 113. Results for Texas: US 90 at the PC (EB).
Before 
1 Mo 
Change 
12 Mo 
Change 


Sample size 
2,825 
2,903 
NA 
2,766 
NA 
Mean speed (mph) 
65.1 
66.7 
1.6 
65.7 
0.6 
SD of mean 
5.9 
5.6 
NA 
6.2 
NA 
85th percentile speed (mph) 
70 
72 
2 
71 
1 
Fraction of vehicles exceeding posted or advisory speed limit 

By 5 mph 
0.02 
0.04 
110.5% 
0.03 
47.4% 
By 10 mph 
> 0.00 
0.01 
75.0%* 
0.01 
25.0%* 
By 15 mph 
> 0.00 
> 0.00 
0.0%* 
> 0.00 
200.0% 
By 20 mph 
> 0.00 
> 0.00 
100.0% 
> 0.00 
0.0%* 
*Not statistically significant at 95percent level of significance
NA = Not applicable
SD = Standard deviation
Table 114. Results for Texas: US 90 at the CC (EB).
Before 
1 Mo 
Change 
12 Mo 
Change 


Sample size 
2,785 
1,443 
NA 
2,789 
NA 
Mean speed (mph) 
66.1 
65.1 
1.0 
64.5 
1.6 
SD of mean 
6.4 
6.1 
NA 
6.8 
NA 
85th percentile speed (mph) 
71 
70 
1 
70 
1 
Fraction of vehicles exceeding posted or advisory speed limit 

By 5 mph 
0.03 
0.02 
29.4% 
0.02 
52.9% 
By 10 mph 
0.01 
> 0.00 
33.3%* 
0.01 
16.7%* 
By 15 mph 
> 0.00 
0.0 
100.0% 
> 0.00 
0.0%* 
By 20 mph 
0.00 
0.0 
0.0%* 
0.0 
0.0%* 
*Not statistically significant at 95percent level of significance
NA = Not applicable
SD = Standard deviation
US 101 in Washington has a posted speed limit of 50 mph with an advisory speed of 30 mph. A dynamic curve display was placed for the EB direction of traffic. The site is about 5 miles southwest of Aberdeen, WA.
Table 115 shows results for the upstream speed control data collection location. Moderate increases in speed occurred for the mean for all of the after periods by about 4 to 5 mph. The 85th percentile speed decreased by 2 mph for the 1month after period, and 1 mph for the 12 and 24month after periods. Minor decreases resulted for the percent of vehicles over the speed limit by 10, 15, or 20 mph or more.
Table 115. Results for Washington: US 101 upstream of curve (EB).
Before 
1 Mo 
Change 
12 Mo 
Change 
24 Mo 
Change 


ADT 
1,963 
1,841 
122 
1,564 
399 
1,489 
474 
Sample size 
3,563 
3,509 
NA 
3,064 
NA 
2,861 
NA 
Mean speed (mph) 
46.7 
50.4 
3.7 
51.6 
4.9 
50.9 
4.2 
SD of mean 
10.9 
7.4 
NA 
7.0 
NA 
7.5 
NA 
85th percentile speed (mph) 
59 
57 
2 
58 
1 
58 
1 
Fraction of vehicles exceeding posted or advisory speed limit 

By 5 mph 
0.27 
27.8 
1.5% 
0.33 
19.0% 
.30 
9.5% 
By 10 mph 
0.14 
7.2 
48.9% 
0.10 
29.1% 
0.07 
49.6% 
By 15 mph 
0.06 
0.02 
73.7% 
0.02 
61.4% 
0.02 
73.7% 
By 20 mph 
0.02 
< 0.00 
85.0% 
0.01 
75.0% 
< 0.00 
90.0% 
ADT = Average daily traffic
NA = Not applicable
SD = Standard deviation
Table 116 provides results for the PC. Major reductions in speed resulted for the 1, 12, and 24month after periods, with speed reductions of up to 5 mph for mean and 85th percentile speeds. Large decreases were also present in the percent of vehicles exceeding the advisory speed by 5, 10, 15, or 20 mph.
As noted, the change in percent of vehicles traveling 15 and 20 mph or more over the advisory speed was more than 30 percent. This suggests the signs were very effective in reducing highend speeds. Decreases were much greater than those noted at the control site.
There were moderate reductions (about 4 percent) in the fraction of vehicles traveling over the advisory speed by 5 mph or more and those traveling 10 mph or more (decreases between 11 and 16 percent). There were also significant decreases in the fraction of vehicles exceeding the advisory speed by 15 mph, with decreases between 27 and 44 percent. In addition, a significant decrease in vehicles traveling 20 mph or more occurred with decreases ranging from 51 to 72 percent.
Table 116. Results for Washington: US 101 at the PC (EB).
Before 
1 Mo 
Change 
12 Mo 
Change 
24 Mo 
Change 


Sample size 
3,400 
3,510 
NA 
2,839 
NA 
2,802 
NA 
Mean speed (mph) 
48.4 
43.3 
5.1 
43.5 
4.9 
44.8 
3.6 
SD of mean 
6.4 
5.8 
NA 
5.6 
NA 
6.3 
NA 
85th percentile speed (mph) 
54 
49 
5 
49 
5 
51 
3 
Fraction of vehicles exceeding posted or advisory speed limit 

By 5 mph 
0.98 
0.94 
4.3% 
0.94 
4.7% 
0.94 
4.1% 
By 10 mph 
0.95 
0.79 
16.2% 
0.80 
15.9% 
0.84 
11.3% 
By 15 mph 
0.78 
0.46 
41.4% 
0.44 
43.6% 
0.57 
26.9% 
By 20 mph 
0.43 
0.14 
68.2% 
0.12 
71.5% 
0.21 
51.3% 
NA = Not applicable
SD = Standard deviation
Reductions also occurred at the CC for all speed metrics, although the changes were not as major as at the PC, as shown in table 117. The major decrease was in 85th percentile speeds at the 1month after period (7 mph). Decreases of 22 percent and 15 percent resulted for the percent of vehicles exceeding the advisory speed by 5 mph for the 1 and 12month after periods, respectively.
Table 117. Results for Washington: US 101 at the CC (EB).
Before 
1 Mo 
Change 
12 Mo 
Change 
24 Mo 
Change 


Sample size 
3,521 
3,499 
NA 
3,061 
NA 
2,861 
NA 
Mean speed (mph) 
38.6 
35.7 
2.9 
36.6 
2.0 
37.0 
1.6 
SD of mean 
4.6 
5.1 
NA 
4.6 
NA 
4.8 
NA 
85th percentile speed (mph) 
43 
36 
7 
41 
2 
42 
1 
Fraction of vehicles exceeding posted or advisory speed limit 

By 5 mph 
0.85 
0.63 
26.2% 
0.71 
17.4% 
0.74 
13.8% 
By 10 mph 
0.39 
0.22 
44.7% 
0.26 
33.9% 
0.29 
26.0% 
By 15 mph 
0.08 
0.03 
59.0% 
0.04 
47.4% 
0.05 
34.6% 
By 20 mph 
0.01 
<0.00 
69.2% 
0.01 
61.5% 
0.00 
100.0% 
NA = Not applicable
SD = Standard deviation
The change for the percent of vehicles traveling 10 mph or more over the advisory speed changed by 17 and 13 percent for the 1 and 12month after periods, respectively. Moderate decreases of 2 mph occurred for mean and 85th percentile speeds for the 12month after period, and about 1 mph for the 24month after period. Moderate decreases occurred in the fraction of vehicles traveling 5 or 10 mph over, with decreases of 14 to 26 percent, and decreases of 26 to 45 percent for vehicles traveling 10 mph or more advisory speed.
Decreases between 35 and 59 percent resulted for the percent traveling over the 15 mph. Decreases for vehicles traveling 20 mph or more over were between 62 and 100 percent.
SR 7 in Washington has a posted speed limit of 50 mph with an advisory speed of 35 mph. A dynamic speed display was placed for the EB direction of traffic. The site is 33 miles south of Tacoma, WA. The sign was installed in August 2008. The sign was vandalized in July 2009 and replaced. The sign was vandalized again in December 2009. Because the team had already made a number of unexpected visits to do sign maintenance, it was determined that it was not feasible to make another site visit, so the sign was not replaced, and data were not collected at the 24month after period.
Table 118 shows results for the upstream speed control data collection location. A moderate decrease in mean speed occurred for the 1month after period (1.8 mph), and a moderate increase (2.3 mph) occurred for 12month after period. The 85th percentile speed and percent of vehicles over the speed limit decreased for the 1month after period except for the percent of vehicles traveling 20 mph or more over the posted speed limit. All but the percent of vehicles traveling 20 mph or more over the posted speed limit increased slightly for the 12month after period.
Table 118. Results for Washington: SR 7 upstream of curve (EB).
Before 
1 Mo 
Change 
12 Mo 
Change 


ADT 
837 
1,318 
481 
1,318 
481 

Sample size 
1,634 
2,598 
NA 
1,138 
NA 

Mean speed (mph) 
49.4 
47.6 
1.8 
51.7 
2.3 

SD of mean 
7.0 
6.5 
NA 
5.8 
NA 

85th percentile speed (mph) 
56 
54 
2 
57 
1 

Fraction of vehicles exceeding posted or advisory speed limit 

By 5 mph 
0.21 
0.12 
40.7% 
0.29 
38.8% 

By 10 mph 
0.06 
0.04 
31.3% 
0.07 
14.1%* 

By 15 mph 
0.02 
0.01 
23.5% 
0.02 
29.4%* 

By 20 mph 
0.01 
0.01 
16.7% 
<0.00 
33.3%* 
ADT = Average daily traffic
NA = Not applicable
SD = Standard deviation
Table 119 presents results for the PC for SR 7. Moderate decreases occurred for the change in mean and 85th percentile speeds. A very significant decrease in the percent of vehicles traveling over the advisory speed of 35 mph by 5, 10, 15, and 20 mph occurred for the 1month after period, with a change of 32.0 percent for 5 mph or more and a change of 60.5 percent for 10 mph or more. The decreases were smaller for the 12month after period than for the 1month after period.
Table 119. Results for Washington: SR 7 at the PC (EB).
Before 
1 Mo 
Change 
12 Mo 
Change 


Sample size 
1,588 
2,569 
NA 
1,147 
NA 
Mean speed (mph) 
43.1 
39.9 
3.2 
41.4 
1.7 
SD of mean 
6.5 
5.5 
NA 
5.8 
NA 
85th percentile speed (mph) 
50 
45 
5 
47 
3 
Fraction of vehicles exceeding posted or advisory speed limit 

By 5 mph 
0.73 
0.49 
32.0% 
0.59 
18.5% 
By 10 mph 
0.45 
0.18 
60.5% 
0.27 
40.4% 
By 15 mph 
0.15 
0.05 
65.6% 
0.09 
41.7% 
By 20 mph 
0.03 
0.01 
56.0% 
0.01 
44.0% 
NA = Not applicable
SD = Standard deviation
Table 120 presents results for the CC data collection location. Moderate decreases in 85th percentile speed and percent over the advisory speed by 5, 10, and 15 mph were noted for the 1month after period. All speeds, however, increased for the 12month after period, with a 4mph increase in mean speed and 2mph increase for 85th percentile speeds. Speed increases were similar for those noted at the control site.
Table 120. Results for Washington: SR 7 at the CC (EB).
Before 
1 Mo 
Change 
12 Mo 
Change 


ADT 
814 
1,323 
509 
1,463 
649 
Sample size 
1,561 
2,569 
NA 
1,440 
NA 
Mean speed (mph) 
38.3 
38.8 
0.5 
42.0 
3.7 
SD of mean 
9.6 
5.3 
NA 
6.8 
NA 
85th percentile speed (mph) 
47 
44 
3 
49 
2 
Fraction of vehicles exceeding posted or advisory speed limit 

By 5 mph 
0.55 
0.40 
28.3% 
0.59 
6.7% 
By 10 mph 
0.26 
0.14 
45.6% 
0.28 
8.9% 
By 15 mph 
0.06 
0.04 
38.6% 
0.14 
136.8% 
By 20 mph 
0.01 
0.01 
0.0%* 
0.05 
575.0% 
NA = Not applicable
SD = Standard deviation