U.S. Department of Transportation
Federal Highway Administration
1200 New Jersey Avenue, SE
Washington, DC 20590
202-366-4000
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: FHWA-HRT-14-020 Date: January 2015 |
Publication Number: FHWA-HRT-14-020 Date: January 2015 |
Changes in speed were compared for daytime versus nighttime for a select group of sites to assess whether the signs were more likely to be effective for one temporal period or the other. Data were evaluated for the before period and 12-month after period for seven sites. The 12-month after period was used because the signs would have been placed at that point for some time and any novelty effect would have worn off.
Data for each period were disaggregated by daytime and nighttime periods. Daytime was defined as 15 min after sunrise until 15 min before sunset as determined by reported sunrise and sunset time for the dates when data were collected. Nighttime was considered as 15 min after sunset until 15 min before sunrise. Data for the 30-min period around sunrise and sunset were discarded. Data were compared at the PC as well as at the CC.
Speed metrics were first compared for daytime versus nighttime for both the before and 12-month after period. This comparison was done to determine whether speeds were similar for daytime versus nighttime. Change was calculated by subtracting daytime speeds from nighttime speeds.
Speed metrics were also compared for daytime periods and then compared with nighttime periods. Daytime speed data for the before period was subtracted for daytime data at the 12-month after period. Similarly, nighttime speed data for the before period was subtracted for nighttime data at the 12-month after period. Changes in speed metrics were then compared between the two periods.
The tables in this appendix show the actual change in the fraction of vehicles traveling 5, 10, 15, or 20 mph or more over the posted or advisory speed rather than showing percent change as was done in the main section of the report.
Table 121 shows speeds for vehicles during the daytime compared with speeds for the nighttime for Washington site US 101. Nighttime speeds are lower than daytime speeds for both the before and 12-month after periods at the PC, but most differences are not statistically significant. Similarly, nighttime speeds were marginally lower during the nighttime at the CC both before and 12 months after installation of the signs.
Table 122 shows changes in speed metrics for the daytime period compared with the nighttime period. At the PC, decreases were slightly less for the nighttime period than for the daytime period, although the differences were minor. Daytime decrease at the CC was also greater than for nighttime, but the differences were also small.
Table 121. Comparison of speed changes daytime versus nighttime for Washington US 101.
|
At Point of Curvature |
At Center of Curve |
||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
Before |
12 mo |
Before |
12 mo |
|||||||||
Day |
Night |
Change |
Day |
Night |
Change |
Day |
Night |
Change |
Day |
Night |
Change |
|
Mean speed |
48.8 |
47.1 |
-1.7 |
43.5 |
42.9 |
-0.6* |
38.6 |
38.3 |
-0.3* |
36.6 |
36.6 |
0* |
85th percentile speed |
54 |
54 |
0 |
49 |
49 |
0 |
43 |
43 |
0 |
41 |
41 |
0 |
Percent vehicles exceeding posted or advisory speed limit |
||||||||||||
By 5 mph |
98.4% |
97.9% |
-0.6%* |
93.7% |
92.2% |
-1.5%* |
85.8% |
83.4% |
-2.4%* |
70.4% |
69.9% |
-0.5%* |
By 10 mph |
94.8% |
94.2% |
-0.6%* |
79.7% |
75.8% |
-3.9%* |
39.6% |
37.4% |
-2.2%* |
25.2% |
27.9% |
2.6%* |
By 15 mph |
79.7% |
71.2% |
-8.5% |
44.4% |
40.8% |
-3.6%* |
7.9% |
8.6% |
0.7%* |
4.1% |
3.9% |
-0.2%* |
By 20 mph |
45.4% |
32.3% |
-13.1% |
12.2% |
11.9% |
-0.2%* |
1.4% |
1.1% |
-0.3%* |
0.5% |
0.6% |
0.1%* |
*Not statistically significant at the 95-percent level of significance
Table 122. Comparison of speed changes for daytime versus nighttime for Washington US 101.
|
At Point of Curvature |
At Center of Curve |
||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
Daytime |
Nighttime |
Daytime |
Nighttime |
|||||||||
Before |
12 mo |
Change |
Before |
12 mo |
Change |
Before |
12 mo |
Change |
Before |
12 mo |
Change |
|
Mean speed |
48.8 |
43.5 |
-5.3 |
47.1 |
42.9 |
-4.2 |
38.6 |
36.6 |
-2.0 |
38.3 |
36.6 |
-1.7 |
85th percentile speed |
54 |
49 |
-5 |
54 |
49 |
-5 |
43 |
41 |
-2 |
43 |
41 |
-2 |
Percent vehicles exceeding posted or advisory speed limit |
||||||||||||
By 5 mph |
98.4% |
93.7% |
-4.7% |
97.9% |
92.2% |
-5.7% |
85.8% |
70.4% |
-15.4% |
83.4% |
69.9% |
-13.5% |
By 10 mph |
94.8% |
79.7% |
-15.0% |
94.2% |
75.8% |
-18.4% |
39.6% |
25.2% |
-14.4% |
37.4% |
27.9% |
-9.5% |
By 15 mph |
79.7% |
44.4% |
-35.3% |
71.2% |
40.8% |
-30.3% |
7.9% |
4.1% |
-3.8% |
8.6% |
3.9% |
-4.7% |
By 20 mph |
45.4% |
12.2% |
-33.2% |
32.3% |
11.9% |
-20.4% |
1.4% |
0.5% |
-0.9% |
1.1% |
0.6% |
-0.6% |
Table 123 shows speeds for vehicles during the daytime compared with speeds for the nighttime for Washington site SR 7. At the PC, mean nighttime speeds in the before period were 2 mph higher than during the daytime, with an increase of 1 mph for 85th percentile speeds. The percentage of vehicles traveling 5, 10, 15, or 20 mph or more over the advisory speed of 35 mph was also higher for nighttime speeds than daytime speeds. A total of 14.4 percent more vehicles were traveling 5 mph or more over the limit during the nighttime than during the daytime, with 7.2 percent more for those traveling 10 mph or more, and 6.4 and 4.6 percent more traveling 15 or 20 mph or more over the advisory speed limit.
At 12 months, nighttime speeds were still higher, but the difference was smaller, with a 1-mph increase for average and 85th percentile speeds. Results for the CC indicate that nighttime speeds were higher than daytime speeds for the before period, with similar increases as the PC. At 12 months, nighttime speeds were moderately higher than daytime speeds, with average speeds 2.7 mph higher and 85th percentile speeds 6 mph higher. At nighttime, about 16 to 17 percent more vehicles were traveling 5, 10, and 15 mph over the speed limit than during daytime. Almost 9 percent more nighttime vehicles were traveling 20 mph or more over the advisory speed.
Table 124 shows differences for changes in daytime speeds compared with changes in nighttime speeds for Washington site SR 7. At the PC, changes in average nighttime speeds after installation of the sign were twice that for daytime speeds, while changes in 85th percentile speeds were the same.
Decreases in vehicles traveling over the advisory speed at nighttime were about 6 percent higher for vehicles traveling 5 or 10 mph over, and were almost twice that for vehicles traveling 15 or 20 mph over than for daytime.
At the CC, speeds increased for both daytime and nighttime vehicles, with a slightly higher increase in average speed for daytime compared with nighttime (3.9 versus 2.8 mph). Much larger decreases in the percentage of vehicles exceeding the advisory speed occurred during the nighttime than daytime.
Table 123. Comparison of speed changes daytime versus nighttime for Washington SR 7.
|
At Point of Curvature |
At Center of Curve |
||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
Before |
12 mo |
Before |
12 mo |
|||||||||
Day |
Night |
Change |
Day |
Night |
Change |
Day |
Night |
Change |
Day |
Night |
Change |
|
Mean speed |
42.9 |
45.0 |
2.1 |
41.4 |
42 |
0.6 |
37.9 |
41.7 |
3.8 |
41.8 |
44.5 |
2.7 |
85th percentile speed |
49 |
50 |
1 |
47 |
48 |
1 |
46 |
46 |
0 |
48 |
54 |
6 |
Percent vehicles exceeding posted or advisory speed limit |
||||||||||||
By 5 mph |
70.7% |
85.1% |
14.4% |
58.4% |
67.0% |
8.7% |
53.5% |
66.4% |
12.9% |
57.1% |
74.8% |
17.6% |
By 10 mph |
44.0% |
51.2% |
7.2% |
26.9% |
27.5% |
0.5% |
25.5% |
30.3% |
4.8% |
26.7% |
42.7% |
16.0% |
By 15 mph |
14.4% |
19.8% |
5.4% |
8.9% |
9.9% |
1.0% |
5.4% |
7.6% |
2.1% |
12.4% |
29.1% |
16.8% |
By 20 mph |
2.0% |
6.6% |
4.6% |
1.3% |
3.3% |
2.0% |
0.6% |
2.5% |
1.9% |
4.8% |
13.6% |
8.8% |
Table 124. Comparison of speed changes for daytime versus nighttime for Washington SR 7.
|
At Point of Curvature |
At Center of Curve |
||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
Daytime |
Nighttime |
Daytime |
Nighttime |
|||||||||
Before |
12 mo |
Change |
Before |
12 mo |
Change |
Before |
12 mo |
Change |
Before |
12 mo |
Change |
|
Mean speed |
42.9 |
41.4 |
-1.5 |
45.0 |
42.0 |
-3.0 |
37.9 |
41.8 |
3.9 |
41.7 |
44.5 |
2.8 |
85th percentile speed |
49 |
47 |
-2 |
50 |
48 |
-2 |
46 |
48 |
2 |
46 |
54 |
8 |
Percent vehicles exceeding posted or advisory speed limit |
||||||||||||
By 5 mph |
70.7% |
58.4% |
-12.3% |
85.1% |
67.0% |
-18.1% |
53.5% |
57.1% |
3.6% |
66.4% |
74.8% |
8.4% |
By 10 mph |
44.0% |
26.9% |
-17.1% |
51.2% |
27.5% |
-23.8% |
25.5% |
26.7% |
1.2% |
30.3% |
42.7% |
12.5% |
By 15 mph |
14.4% |
8.9% |
-5.6% |
19.8% |
9.9% |
-9.9% |
5.4% |
12.4% |
6.9% |
7.6% |
29.1% |
21.6% |
By 20 mph |
2.0% |
1.3% |
-0.8% |
6.6% |
3.3% |
-3.3% |
0.6% |
4.8% |
4.2% |
2.5% |
13.6% |
11.1% |
Table 125 shows the comparison of nighttime speeds to daytime speeds for Arizona site SR 95. At the PC, nighttime speeds were higher than daytime speeds for both the before and 12-month after periods. Mean speeds for nighttime were 1.7 and 3.2 mph higher, and 85th percentile speeds were 3 mph higher for both periods.
The fraction of vehicles traveling 5, 10, or 15 mph over the advisory speeds was higher by 5 to 14 percent for nighttime compared with daytime, with little difference noted for vehicles traveling 20 mph over the limit.
Table 126 provides change in speeds for the daytime period compared with changes for the nighttime period for Arizona SR 95. Changes in daytime speeds were higher than nighttime speeds at the PC. Average speeds were 4.3 mph compared with 3.0 mph, with a decrease of 4 mph in 85th percentile speeds compared with 3 mph.
Decreases in the fraction of vehicles traveling 5 or 10 mph over the advisory speed limit were about 10 percent lower for daytime than for nighttime, and about 2 to 3 percent lower for 15 and 20 mph over the limit. Results at the CC were similar to those at the PC. Slightly greater decreases were observed for the daytime period than for the nighttime period, but the difference was about 1 mph for mean and 85th percentile speeds.
Table 125. Comparison of speed changes daytime versus nighttime for Arizona SR 95.
|
At Point of Curvature |
At Center of Curve |
||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
Before |
12 mo |
Before |
12 mo |
|||||||||
Day |
Night |
Change |
Day |
Night |
Change |
Day |
Night |
Change |
Day |
Night |
Change |
|
Mean speed |
56.9 |
58.6 |
1.7 |
52.6 |
55.6 |
3.2 |
54.4 |
56.3 |
1.9 |
51.3 |
53.8 |
2.5 |
85th percentile speed |
62 |
65 |
3 |
58 |
62 |
3 |
60 |
63 |
3 |
57 |
59 |
2 |
Percent vehicles exceeding posted or advisory speed limit |
||||||||||||
By 5 mph |
91.7% |
96.1% |
4.3% |
73.4% |
86.9% |
9.3% |
81.4% |
86.4% |
5.0% |
64.9% |
77.5% |
12.6% |
By 10 mph |
68.2% |
75.6% |
7.4% |
31.4% |
49.0% |
21.1% |
49.4% |
59.7% |
10.3% |
26.4% |
42.7% |
16.3% |
By 15 mph |
30.2% |
41.1% |
10.9% |
10.1% |
23.3% |
17.1% |
17.6% |
30.6% |
13.0% |
5.9% |
14.8% |
8.9% |
By 20 mph |
7.7% |
15.7% |
8.0% |
2.5% |
7.7% |
9.2% |
3.7% |
10.9% |
7.3% |
0.8% |
4.3% |
3.5% |
Table 126. Comparison of speed changes for daytime changes versus nighttime changes for Arizona SR 95.
|
At Point of Curvature |
At Center of Curve |
||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
Daytime |
Nighttime |
Daytime |
Nighttime |
|||||||||
Before |
12 mo |
Change |
Before |
12 mo |
Change |
Before |
12 mo |
Change |
Before |
12 mo |
Change |
|
Mean speed |
56.9 |
52.6 |
-4.3 |
58.6 |
55.6 |
-3.0 |
54.4 |
51.3 |
-3.1 |
56.3 |
53.8 |
-2.5 |
85th percentile speed |
62 |
58 |
-4 |
65 |
62 |
-3 |
60 |
57 |
-3 |
63 |
59 |
-4 |
Percent vehicles exceeding posted or advisory speed limit |
||||||||||||
By 5 mph |
91.7% |
73.4% |
-18.3% |
96.1% |
86.9% |
-9.1% |
81.4% |
64.9% |
-16.5% |
86.4% |
77.5% |
-8.9% |
By 10 mph |
68.2% |
31.4% |
-36.9% |
75.6% |
49.0% |
-26.7% |
49.4% |
26.4% |
-23.0% |
59.7% |
42.7% |
-17.1% |
By 15 mph |
30.2% |
10.1% |
-20.1% |
41.1% |
23.3% |
-17.8% |
17.6% |
5.9% |
-11.6% |
30.6% |
14.8% |
-15.8% |
By 20 mph |
7.7% |
2.5% |
-5.1% |
15.7% |
7.7% |
-8.0% |
3.7% |
0.8% |
-2.8% |
10.9% |
4.3% |
-6.6% |
Table 127 shows changes for Arizona site SR 377. No major differences occurred between nighttime and daytime speeds for any of the time periods at the PC. Similar results occurred for the CC.
Table 128 provides change in speeds for the daytime period compared with changes for the nighttime period for Arizona SR 377. As shown, decreases in speed between the before and 12-month after period were moderately larger than for the daytime period at the PC. The daytime decrease in mean speed was 3.4 and change in 85th percentile speed was 4 mph, compared with the nighttime decrease of 4.2 mph and 8 mph, respectively.
Decreases in the fraction traveling over the posted speed limit were also greater for the nighttime versus daytime periods. At the CC, essentially no change occurred from the before to 12-month after period during the daytime, while moderate decreases occurred for the nighttime period.
Table 127. Comparison of speed changes daytime versus nighttime for Arizona SR 377.
|
At Point of Curvature |
At Center of Curve |
||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
Before |
12 mo |
Before |
12 mo |
|||||||||
Day |
Night |
Change |
Day |
Night |
Change |
Day |
Night |
Change |
Day |
Night |
Change |
|
Mean speed |
69.5 |
69.2 |
-0.3 |
66.1 |
65.0 |
-1.1 |
66.4 |
66.4 |
0.0 |
66.8 |
65.9 |
-0.9 |
85th percentile speed |
75 |
78 |
3 |
71 |
70 |
-1 |
72 |
73 |
1 |
72 |
71 |
-1 |
Percent vehicles exceeding posted or advisory speed limit |
||||||||||||
By 5 mph |
47.2% |
50.0% |
2.8% |
23.6% |
19.3% |
-4.3% |
26.4% |
32.7% |
6.3% |
29.3% |
27.8% |
-1.6% |
By 10 mph |
18.3% |
28.6% |
10.3% |
4.3% |
4.5% |
0.3% |
8.0% |
10.1% |
2.1% |
6.1% |
6.5% |
0.4% |
By 15 mph |
6.4% |
10.7% |
4.3% |
1.1% |
1.2% |
0.1% |
2.3% |
3.6% |
1.3% |
1.1% |
0.8% |
-0.3% |
By 20 mph |
2.7% |
3.6% |
0.8% |
0.3% |
0.0% |
-0.3% |
0.6% |
0.0% |
-0.6% |
0.6% |
0.4% |
-0.2% |
Table 128.Comparison of speed changes for daytime changes versus nighttime changes for Arizona SR 377.
|
At Point of Curvature |
At Center of Curve |
||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
Daytime |
Nighttime |
Daytime |
Nighttime |
|||||||||
Before |
12 mo |
Change |
Before |
12 mo |
Change |
Before |
12 mo |
Change |
Before |
12 mo |
Change |
|
Mean speed |
69.5 |
66.1 |
-3.4 |
69.2 |
65.0 |
-4.2 |
66.4 |
66.8 |
0.4 |
66.4 |
65.9 |
-0.5 |
85th percentile speed |
75 |
71 |
-4 |
78 |
70 |
-8 |
72 |
72 |
0 |
73 |
71 |
-2 |
Percent vehicles exceeding posted or advisory speed limit |
||||||||||||
By 5 mph |
47.2% |
23.6% |
-23.6% |
50.0% |
19.3% |
-30.7% |
26.4% |
29.3% |
2.9% |
32.7% |
27.8% |
-5.0% |
By 10 mph |
18.3% |
4.3% |
-14.0% |
28.6% |
4.5% |
-24.0% |
8.0% |
6.1% |
-1.9% |
10.1% |
6.5% |
-3.6% |
By 15 mph |
6.4% |
1.1% |
-5.3% |
10.7% |
1.2% |
-9.5% |
2.3% |
1.1% |
-1.1% |
3.6% |
0.8% |
-2.8% |
By 20 mph |
2.7% |
0.3% |
-2.4% |
3.6% |
0.0% |
-3.6% |
0.6% |
0.6% |
0.0% |
0.0% |
0.4% |
0.4% |
Table 129 compares speeds at night to speeds during the day for Florida site SR 20 (Gainesville). At the PC, nighttime speeds were lower than daytime speeds during the before period and were slightly higher after. The differences, however, were small, with changes in mean and 85th percentile speeds of 1 mph or less. Changes in the fraction of vehicles traveling 5, 10, 15, or 20 mph over the advisory speed were 5 percent or less.
Table 130 provides the comparison of speed changes for the daytime with the nighttime for the 12-month after period for Florida site SR 20 (Gainesville). At the PC, mean speed decreases were slightly larger for daytime than for nighttime (3.1 compared with 2.2 for mean speeds and 4 mph compared with 3 mph for 85th percentile).
The decreases in the fraction of vehicles traveling 5 or mph over the advisory speed were almost twice as much for the nighttime period. Decreases for the fraction of vehicles traveling 10 mph over were 20.8 percent for the daytime period compared with 14.7 percent for the nighttime period. The decrease in the fraction of vehicles traveling 15 mph or more over was 27.3 percent for the daytime compared with 19.2 percent for the nighttime. The daytime period decrease for 20 mph or more over the advisory speed was 1.5 percent greater than for the nighttime period.
Table 129. Comparison of speed changes daytime versus nighttime for Florida SR 20-Gainesville.
|
At Point of Curvature |
At Center of Curve |
||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
Before |
12 mo |
Before |
12 mo |
|||||||||
Day |
Night |
Change |
Day |
Night |
Change |
Day |
Night |
Change |
Day |
Night |
Change |
|
Mean speed |
58.0 |
57.4 |
-0.6 |
54.9 |
55.2 |
0.3 |
58.3 |
58.0 |
-0.3 |
54.3 |
55.0 |
0.7 |
85th percentile speed |
63 |
63 |
0.0 |
59 |
60 |
1 |
63 |
64 |
1.0 |
59 |
60 |
1 |
Percent vehicles exceeding posted or advisory speed limit |
||||||||||||
By 5 mph |
94.2% |
90.9% |
-3.3% |
90.5% |
89.2% |
-1.3% |
95.5% |
93.2% |
-2.3% |
88.4% |
88.9% |
0.5% |
By 10 mph |
78.0% |
73.4% |
-4.6% |
57.2% |
58.7% |
1.5% |
80.6% |
75.9% |
-4.7% |
52.5% |
56.5% |
4.0% |
By 15 mph |
39.5% |
36.2% |
-3.3% |
12.2% |
17.1% |
4.9% |
41.1% |
41.8% |
0.6% |
10.5% |
16.5% |
5.9% |
By 20 mph |
9.8% |
10.0% |
0.3% |
1.8% |
3.6% |
1.8% |
10.0% |
11.3% |
1.3% |
1.5% |
3.5% |
1.9% |
Table 130. Comparison of speed changes for daytime changes versus nighttime changes for Florida SR 20-Gainesville.
|
At Point of Curvature |
At Center of Curve |
||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
Daytime |
Nighttime |
Daytime |
Nighttime |
|||||||||
Before |
12 mo |
Change |
Before |
12 mo |
Change |
Before |
12 mo |
Change |
Before |
12 mo |
Change |
|
Mean speed |
58.0 |
54.9 |
-3.1 |
57.4 |
55.2 |
-2.2 |
58.3 |
54.3 |
-4.0 |
58.0 |
55.0 |
-3.0 |
85th percentile speed |
63 |
59 |
-4 |
63 |
60 |
-3 |
63 |
59 |
-4 |
64 |
60 |
-4 |
Percent vehicles exceeding posted or advisory speed limit |
||||||||||||
By 5 mph |
94.2% |
90.5% |
-3.8% |
90.9% |
89.2% |
-1.8% |
95.5% |
88.4% |
-7.0% |
93.2% |
88.9% |
-4.3% |
By 10 mph |
78.0% |
57.2% |
-20.8% |
73.4% |
58.7% |
-14.7% |
80.6% |
52.5% |
-28.0% |
75.9% |
56.5% |
-19.3% |
By 15 mph |
39.5% |
12.2% |
-27.3% |
36.2% |
17.1% |
-19.2% |
41.1% |
10.5% |
-30.6% |
41.8% |
16.5% |
-25.3% |
By 20 mph |
9.8% |
1.8% |
-8.0% |
10.0% |
3.6% |
-6.5% |
10.0% |
1.5% |
-8.5% |
11.3% |
3.5% |
-7.8% |
Table 131 shows the differences between daytime and nighttime speeds for Florida site SR 267. At the PC, very little difference was noted for the daytime versus nighttime periods before and 12 months after installation of the sign. Results were similar for the CC. Differences in average and 85th percentile speeds were 1 mph or less for both the before and 12-month after period.
Table 132 provides change in speed for the daytime period compared with changes for the nighttime period for Florida SR 267. At the PC, decreases in mean and 85th percentile speeds for the 12-month after period were within 1 mph for the daytime compared with the nighttime period.
Decreases in the fraction of vehicles traveling 5, 10, 15, or 20 mph over the posted speed were within 2 percent for daytime compared with nighttime. Similar results were found for the CC. Differences in decreases for mean and 85th percentile speeds were within 1 mph. Differences in the fraction of vehicles traveling over the posted speed were also within 2 percent.
Table 131. Comparison of speed changes daytime versus nighttime for Florida SR 267.
|
At Point of Curvature |
At Center of Curve |
||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
Before |
12 mo |
Before |
12 mo |
|||||||||
Day |
Night |
Change |
Day |
Night |
Change |
Day |
Night |
Change |
Day |
Night |
Change |
|
Mean speed |
54.5 |
54.3 |
-0.2 |
47.7 |
47.8 |
-0.2 |
53.3 |
53.4 |
0.1 |
51.0 |
51.9 |
0.9 |
85th percentile speed |
60 |
60 |
0.0 |
53 |
52 |
0.0 |
59 |
60 |
1.0 |
57 |
58 |
1 |
Percent vehicles exceeding posted or advisory speed limit |
||||||||||||
By 5 mph |
15.5% |
17.3% |
1.8% |
0.8% |
0.6% |
1.8% |
11.8% |
15.4% |
3.6% |
6.8% |
8.4% |
1.5% |
By 10 mph |
2.6% |
4.4% |
1.8% |
0.2% |
0.1% |
1.8% |
1.7% |
3.7% |
1.9% |
1.0% |
1.3% |
0.3% |
By 15 mph |
0.8% |
1.0% |
0.2% |
0.0% |
0.0% |
0.2% |
0.4% |
0.6% |
0.3% |
0.1% |
0.2% |
0.1% |
By 20 mph |
0.1% |
0.2% |
0.1% |
0.0% |
0.0% |
0.1% |
0.0% |
0.1% |
0.1% |
0.0% |
0.0% |
0.0% |
Table 132. Comparison of speed changes for daytime changes versus nighttime changes for Florida SR 267.
|
At Point of Curvature |
At Center of Curve |
||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
Daytime |
Nighttime |
Daytime |
Nighttime |
|||||||||
Before |
12 mo |
Change |
Before |
12 mo |
Change |
Before |
12 mo |
Change |
Before |
12 mo |
Change |
|
Mean speed |
54.5 |
47.7 |
-6.8 |
54.3 |
47.8 |
-6.5 |
53.3 |
51.0 |
-2.3 |
53.4 |
51.9 |
-1.5 |
85th percentile speed |
60 |
53 |
-7 |
60 |
52 |
-8 |
59 |
57 |
-2 |
60 |
58 |
-2 |
Percent vehicles exceeding posted or advisory speed limit |
||||||||||||
By 5 mph |
15.5% |
0.8% |
-14.7% |
17.3% |
0.6% |
-16.7% |
11.8% |
6.8% |
-4.9% |
15.4% |
8.4% |
-7.0% |
By 10 mph |
2.6% |
0.2% |
-2.4% |
4.4% |
0.1% |
-4.3% |
1.7% |
1.0% |
-0.7% |
3.7% |
1.3% |
-2.3% |
By 15 mph |
0.8% |
0.0% |
-0.8% |
1.0% |
0.0% |
-1.0% |
0.4% |
0.1% |
-0.3% |
0.6% |
0.2% |
-0.4% |
By 20 mph |
0.1% |
0.0% |
-0.1% |
0.2% |
0.0% |
-0.2% |
0.0% |
0.0% |
0.0% |
0.1% |
0.0% |
-0.1% |
Table 133 gives the change in speeds for the daytime period compared with changes for the nighttime period for Florida site SR 20 (Tallahassee). The difference between nighttime and daytime speeds for the before period at the PC are minimal, with differences in mean and 85th percentile speeds of 1 mph or less and differences in fraction of vehicles traveling over the advisory speed of 1 percent or less. At 12 months, daytime speeds are slightly greater than daytime, but differences in mean and 85th percentile speeds are 1 mph or less and decreases in the fraction of vehicles of 3 mph or less. Changes at the CC are similar, with nighttime speeds slightly greater than daytime speeds at both the before and 12-month after period. In all cases, differences were not statistically significant at the 95-percent level of significance.
Table 134 shows changes in speed for the daytime period compared with the nighttime period. At the PC, decreases in mean speed and 85th percentile speeds were about 2 mph for both the daytime and nighttime period. Changes in the fraction of vehicles exceeding the posted speed limit by 5, 10, 15, and 20 mph for the daytime and nighttime periods were within 2 percent. Results were similar for the CC. Decreases in mean speed and 85th percentile speeds were about 2 mph for both the daytime and nighttime period. Decreases in the fraction of vehicles exceeding the posted speed by 5 mph or more were slightly greater for the daytime period than for the nighttime period (13.7 percent versus 7.8 percent). Decreases in the fraction of vehicles exceeding the posted speed by 10 mph or more were greater for the nighttime period than for the daytime period (4.1 percent versus 2.5 percent).
In summary, comparison of nighttime speeds to daytime speeds for the seven sites that were evaluated indicated that at the PC, in the majority of cases (57 percent) daytime speeds were similar to nighttime speeds. In 29 percent of the cases, nighttime speeds were slightly or moderately higher than daytime speeds, while in 14 percent of cases daytimes speeds were moderately higher.
Results were exactly the same at the CC. Speeds were similar for nighttime and daytime in the majority of cases (57 percent), while nighttime speeds were higher in 29 percent of the cases and daytime speeds were higher in 14 percent of cases.
When comparing changes in daytime speeds for the 12-month after period compared to the before period to changes in nighttime speeds also for the 12-month after period, little difference resulted in 43 percent of the cases for both the PC and the CC. At the PC, in 29 percent of the cases, decreases in nighttime speeds were moderately higher than decreases in daytime speeds, and daytime decreases were moderately higher for the daytime after periods compared with nighttime. At the CC, the nighttime speeds increased in 14 percent of the cases compared with changes in daytime speeds. Consequently, it can be assumed that few differences occurred between the daytime and nighttime periods. As a result, there is little evidence to suggest that nighttime and daytime periods should be compared separately.
Table 133. Comparison of speed changes daytime versus nighttime for Florida SR 20 - Tallahassee
|
At Point of Curvature |
At Center of Curve |
||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
Before |
12 mo |
Before |
12 mo |
|||||||||
Day |
Night |
Change |
Day |
Night |
Change |
Day |
Night |
Change |
Day |
Night |
Change |
|
Mean speed |
57.3 |
57.3 |
0.0* |
55.2 |
55.6 |
0.4* |
58.2 |
58.6 |
0.4* |
56.7 |
57.6 |
0.9* |
85th percentile speed |
61 |
62 |
1.0 |
59 |
60 |
1 |
62 |
63 |
1.0 |
61 |
62 |
1.0 |
Percent vehicles exceeding posted or advisory speed limit |
||||||||||||
By 5 mph |
26.3% |
26.6% |
0.3%* |
13.1% |
16.4% |
3.4%* |
36.2% |
38.0% |
1.9%* |
22.4% |
30.2% |
7.8%* |
By 10 mph |
4.4% |
5.7% |
1.2%* |
2.1% |
3.0% |
0.9%* |
6.3% |
9.4% |
3.1%* |
3.8% |
5.2% |
1.5%* |
By 15 mph |
0.6% |
1.9% |
1.3%* |
0.4% |
0.7% |
0.4%* |
0.6% |
2.2% |
1.6%* |
0.4% |
1.1% |
0.7%* |
By 20 mph |
0.1% |
0.5% |
0.3%* |
0.1% |
0.2% |
0.1%* |
0.0% |
0.8% |
0.7%* |
0.1% |
0.3% |
0.2%* |
*Not statistically significant at 95-percent level of significance
Table 134. Comparison of speed changes for daytime changes versus nighttime changes for Florida SR 20-Tallahassee
|
At Point of Curvature |
At Center of Curve |
||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
Daytime |
Nighttime |
Daytime |
Nighttime |
|||||||||
Before |
12 mo |
Change |
Before |
12 mo |
Change |
Before |
12 mo |
Change |
Before |
12 mo |
Change |
|
Mean speed |
57.3 |
55.2 |
-2.1 |
57.3 |
55.6 |
-1.7 |
58.2 |
56.7 |
-1.5 |
58.6 |
57.6 |
-1.0 |
85th percentile speed |
61 |
59 |
-2 |
62 |
60 |
-2 |
62 |
61 |
-1 |
63 |
62 |
-1 |
Percent vehicles exceeding posted or advisory speed limit |
||||||||||||
By 5 mph |
26.3% |
13.1% |
-13.2% |
26.6% |
16.4% |
-10.2% |
36.2% |
22.4% |
-13.7% |
38.0% |
30.2% |
-7.8% |
By 10 mph |
4.4% |
2.1% |
-2.4% |
5.7% |
3.0% |
-2.7% |
6.3% |
3.8% |
-2.5% |
9.4% |
5.2% |
-4.1% |
By 15 mph |
0.6% |
0.4% |
-0.2%* |
1.9% |
0.7% |
-1.1% |
0.6% |
0.4% |
-0.2%* |
2.2% |
1.1% |
-1.1%* |
By 20 mph |
0.1% |
0.1% |
-0.0%* |
0.5% |
0.2% |
-0.3%* |
0.0% |
0.1% |
0.1%* |
0.8% |
0.3% |
-0.5%* |
*Not statistically significant at 95-percent level of significance
