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Publication Number:  FHWA-HRT-17-082    Date:  December 2017
Publication Number: FHWA-HRT-17-082
Date: December 2017

 

Safety Evaluation of Signalized Restricted Crossing U-Turn Intersections

Chapter 5. Results

Sites

The project team identified 28 signalized RCUTs from 5 States (Alabama, Michigan, North Carolina, Ohio, and Texas). After some investigation, they eliminated two sites in Michigan because the RCUTs were installed in the mid-1990s, and crash data were no longer available from the before period. The project team obtained aerial photos of the remaining 26 sites to review for substantial changes in the roadways or surrounding land uses between the before period and after period. Such changes would likely confound the RCUT installation and make determination of the effects of the RCUT installation impossible. On this basis, the project team eliminated 15 sites. The most common confounding change resulting in site elimination was that the RCUT was installed at the same time the intersection traffic control changed from unsignalized to signalized. Table 3 identifies the final sites selected for evaluation, which included 11 sites in 4 States where signalized RCUTs were installed during years lending themselves to evaluation, and the RCUT installation was the only substantial change at the location.

Table 3. RCUT treatment sites.

State

County

Intersection

Alabama

Houston

US-231 NW of Dothan at Plum Rd.

Alabama

Houston

US-231 NW of Dothan at Retail Dr.

North Carolina

New Hanover

US-421 south of Piner Rd., Wilmington

Ohio

Butler

OH-4 in Hamilton at Symmes Rd.

Ohio

Butler

OH-4 in Hamilton at Tylersville Rd.

Ohio

Butler

OH-4 in Hamilton at Hamilton-Mason Rd.

Texas

Bexar

US-281 north of San Antonio at Evans Rd.

Texas

Bexar

US-281 north of San Antonio at Stone Oak Pkwy./TPC Pkwy.

Texas

Bexar

Loop-1604 west of San Antonio at New Guibeau

Texas

Bexar

Loop-1604 west of San Antonio at Shaenfield

Texas

Travis

TX-71 in Del Valle east of Austin at FM-973/Fallwell Ln.

Table 4 shows the major geometric characteristics of the treatment sites after RCUT construction. Two numbers in a cell means that two approaches to the intersection had those two different values for the parameter. The treatment sites have much in common besides having signalized RCUTs. They are all in suburban areas, on four-lane or six-lane divided arterials, and characterized by high-speed traffic and minimal crossing pedestrians; as a result, the CMFs emerging from this effort will apply to this type of site. Most of the signalized RCUT installations of which the project team is aware that are planned for the next few years share these characteristics.

Table 4. Important design features of sites after RCUT installation.

Parameter

1

2

3

4

5

6

7

8

9

10

11

Intersection angle (degrees)

90

70

80

70

80

80

60

80

90

90

70

90

70

80

Main street speed limit (mph)

45

40

45

50

50

55

60

60

60

60

60

65

Minor street speed limit (mph)

30

20

25

40

40

40

40

40

35

40

35

55

Main street number of through lanes each direction

3

3

2

3

3

2

2

3

2

2

3

3

3

Minor street number of lanes entering intersection each direction

2

1

2

2

3

2

3

2

3

3

3

2

3

1

2

North or west left-turn crossover number of lanes

2

2

1

1

1

1

2

2

2

N/A

1

South or east left-turn crossover number of lanes

2

1

1

1

1

1

2

2

N/A

2

1

North or west U-turn crossover number of lanes

1

1

1

2

2

1

2

2

2

N/A

2

South or east U-turn crossover number of lanes

1

1

1

2

1

2

2

2

N/A

2

2

Distance center of intersection to north or west U-turn crossover (ft)

870

930

890

850

950

950

1,080

1,100

1,560

N/A

1,720

Distance center of intersection to south or east U-turn crossover (ft)

750

620

1,290

830

1,000

1,060

1,080

1,310

N/A

1,340

1,180

Major street channelized right turns

No

No

No

Yes

Yes

Yes

Yes

Yes

Yes

Yes

No

Minor street channelized right turns

No

No

No

No

No

No

Yes

Yes

No

Yes

No

Crosswalks at main intersection

Yes

Yes

No

No

No

No

Yes

Yes

No

Yes

Yes

Major street median width (ft)

40

40

26

46

34

46

52

52

73

71

58

Minor street median width (ft)

14

12

12

12

12

12

21

2–42

15

4

4

Other interesting design features

None

North U-turn at signal-ized inter-section

Sharp curve on west leg

None

None

None

None

None

3-legged

3-legged

Signal-ized left- turn cross-over west of main inter-section

N/A = not applicable; 1 = Alabama-Plum; 2 = Alabama-Retail; 3 = North Carolina; 4 = Ohio-Symmes; 5 = Ohio-Tylersville; 6 = Ohio-Hamilton-Mason; 7 = Texas-Evans; 8 = Texas-Stone Oak; 9 = Texas-New Guibeau; 10 = Texas-Shaenfield; 11 = Texas-71.

After identifying treatment sites and potential comparison sites, the project team contacted officials in each of the four States for the necessary data. State officials provided information on the RCUTs’ construction dates and crash data for the most recent 5 full years before the start of construction, through the construction year(s), up to the most recent available data. The project team decided 5 years of before data was desirable to boost the sample size and to provide the longest possible test of the quality of the comparison sites. The project team also reviewed the available aerial photos for each treatment site to ensure that no substantive changes had occurred during the 5-year before period.

States also provided data on all reported crashes that occurred within 1,500 ft of the main intersection along the major street and within 500 ft along the minor street for treatment sites. These distances ensured that all crashes related to the RCUT—especially those at the U-turn crossovers—were included in the dataset, while midblock crashes were excluded. The project team adjusted the data collection boundary in several instances due to geometric design differences. Two sites in Texas had longer distances to crossovers, so the boundary was extended. Two Alabama sites—US-231 northwest of Dothan at Plum Road and Retail Drive—had other intersections 1,200 ft and 1,000 ft from the main intersections. Thus, the team set the data collection boundary at 1,000 ft at Plum Road and 800 ft at Retail Drive.

Additionally, States provided traffic volume data at and around each treatment site and information on changes to the intersection geometry accompanying the RCUT construction. The States also provided the following crash reporting thresholds:

The thresholds did not change in any State during the study period. It is important to note the difference between Alabama’s threshold and the other three States’ threshold.

In the course of contacting officials in the 4 States for crash and other data for the 11 RCUT treatment sites and associated potential comparison sites, the project team also asked the officials why the RCUTs were installed. This information was important when selecting the analysis methodology. If treatments were installed as the result of a high-crash site identification process, regression to the mean is likely to result in a natural decrease in the number of crashes in the after period; methods to adjust for this threat should be used. On the other hand, if the treatments were installed for reasons other than to mitigate safety concerns, regression to the mean is not a potential bias to the study. Regression to the mean may occur from the before period to the after period, but it is just as likely to result in an increase as a decrease in the number of crashes. In this case, methods to adjust for regression to the mean are not needed and may be harmful if they are not executed appropriately. The responding officials in all four participating States indicated that all RCUTs were chosen for operational reasons, including to accommodate future growth in traffic, not due to a high number of crashes. All officials indicated safety was considered and that RCUTs were expected to perform well on the safety dimension but was not a case of selecting the design as a safety treatment for an identified high-crash site.

Table 5 summarizes the crash data provided for the treatment sites. There were some deviations from the desired 5 years of before-period data at some sites due to data availability, most prominently at the Texas sites where no crash data were available before 2009. Also, before-period data from 2003 to 2006 were collected at the Hamilton-Mason Road site in Ohio because crash data from 2007 to 2009 had reporting inconsistencies. The project team collected the oldest 5 years of after-period data available for the North Carolina site.

One way to confirm whether regression to the mean is a serious threat to the validity of an analysis is to look for a significant drop in crashes on average in the year before treatment compared to previous years. The decision to install the countermeasure is likely made without benefit of the crash data from that last year before construction, so if regression to the mean were to manifest in the time series, it would likely do so starting in that year. The project team was able to examine this trait at 8 of the 11 treatment sites, since data for Ohio-Hamilton-Mason were not available in the year before construction, and only 1 year of before-period data was available at the Texas-Evans and Texas-Stone Oak sites. Table 6 shows a summary of the year before construction data and reveals that only two of the eight sites—Alabama-Retail and Texas-Shaenfield—had a significant drop in crashes during the year before construction. At the other six sites, the number of crashes either matched the average from the previous years or rose. It appears that regression to the mean was indeed not a serious threat to the validity of this analysis.

Table 5. Reported crashes by year for the RCUT treatment sites.

Site

2002

2003

2004

2005

2006

2007

2008

2009

2010

2011

2012

2013

2014

AL-Plum

--

--

38

31

19

45

35

*

*

*

14

26

--

AL-Retail

--

--

13

12

10

6

3

*

*

*

0

3

--

NC

44

32

46

38

40

*

36

25

36

26

36

--

--

OH-Symmes

--

--

--

24

24

19

24

22

*

*

27

43

--

OH-Tylersville

--

--

--

22

24

16

16

26

*

*

16

8

--

OH-Hamilton-Mason

--

16

12

19

33

--

--

--

*

*

2

7

--

TX-Evans

--

--

--

--

--

--

--

103

*

97

93

135

--

TX-Stone Oak

--

--

--

--

--

--

--

42

*

40

44

85

--

TX-New Guibeau

--

--

--

--

--

--

--

52

51

*

32

30

--

TX-Shaenfield

--

--

--

--

--

--

--

50

31

*

36

46

--

TX-71

--

--

--

--

--

--

--

41

40

30

45

*

16

AL = Alabama; NC = North Carolina; OH = Ohio; TX = Texas.
*Construction years.
--No data.

Table 6. Crash frequency at RCUT treatment sites in the year before construction compared to previous years.

Site

Average Number of Crashes per Year in Years Before the Last Year Prior to Construction

Number of Crashes in the Last Year Prior to Construction

AL-Plum

33

35

AL-Retail

10

3

NC

40

40

OH-Symmes

23

22

OH-Tylersville

20

26

TX-New Guibeau

52

51

TX-Shaenfield

50

31

TX-71

37

45

AL = Alabama; NC = North Carolina; OH = Ohio; TX = Texas.

Adjustment for Traffic Volume

This section reports the results from the analysis that adjusted for an estimated change in traffic volume between the before and after periods. Traffic volume may change due to development in the area, economic changes that affect travel, or changes in overall levels of motorization. Except for the Texas-71 site, the project team obtained traffic volume data from at least one official count or estimate by the responsible agency for at least one station near each site in the before period and the after period. If the responsible agency provided a count or estimate at more than one station and/or year in a before or after period at a particular site, the project team averaged all available counts. Table 7 summarizes the traffic volume data. The data for the Texas-Evans and Texas-Stone Oak sites are from counts on the major and minor streets, while count data for the other sites are from the major street only.

Table 7. Traffic volume data for each site (in thousands of vehicles per day).

Site

2003

2004

2005

2006

2007

2008

2009

2010

2011

2012

2013

AL-Plum

26

26

27

27

25

25

25*

26*

25*

27

27

AL-Retail

36

36

36

36

36

35

36*

37*

36*

39

37

NC

35

--

37

--

38*

--

36

--

38

--

--

OH-Symmes

20

--

--

--

19

--

--

*

*

25

--

OH-Tylersville

20

--

--

--

19

--

--

*

*

17

--

OH-Hamilton-Mason

12

--

--

--

12

--

--

*

16*

17

--

TX-Evans

--

--

93

102

112

102

104

133*

110

110

110

TX-Stone Oak

--

--

84

80

78

80

80

80*

89

89

89

TX-New Guibeau

--

--

61

71

69

71

71

65

80*

83

83

TX-Shaenfield

--

--

61

66

69

67

66

50

70*

79

79

TX-71

10

9

9

10

11

--

10

10

10

10

12*

AL = Alabama; NC = North Carolina; OH = Ohio; TX = Texas.
*Construction years.
--No data.

Table 8 shows the results from the analysis of all crashes after accounting for changes in traffic volumes from the before period to the after period. The safety effect is represented by a CMF. The crash reduction factor (CRF) is calculated as 1 minus the CMF value, converted from a proportion to a percentage. As discussed in the methodology section, a CMF equal to 1.0 implies that the treatment is not expected to change the number of crashes, while a CMF below 1 implies that the treatment is expected to reduce crashes. There was no available traffic volume estimate for the Texas-71 site; therefore, the project team could not compute CMF with this method.

Table 8 also shows the estimated SD of each CMF, which can be used to produce an approximate confidence interval for the CMF and determine whether it is significantly different from 1.0 at a particular significance level. If a CMF is 1 SD from 1.0, that corresponds to a 68-percent confidence level that the actual value is different from 1.0. If a CMF is 1.96 SDs from 1.0, that corresponds to a 95-percent confidence level. Among other things, the SD of a CMF is a useful indicator of the adequacy of the sample size, with small SDs usually associated with large samples of crashes.

As shown in table 8, eight sites had a CMF less than 1.0, and two sites had CMF values greater than 1.0. The North Carolina site, both Alabama sites grouped together, and all three Ohio sites grouped together had CMF values well under 1.0, while the Texas sites as a group had a CMF close to 1.0. All 10 sites grouped together had a CMF of more than 1.0, due to the influence of the large sample size from the Texas-Stone Oak site sample size. SDs were reasonable, ranging from 0.09 to 0.25.

The results in table 8 are based on the sums of the traffic volumes from the individual sites. This gives rise to the possibility that the results were skewed by higher volume sites. To account for this possibility, the project team reanalyzed the last five rows in table 8 using volume indices rather than totals (i.e., normalizing the volume at each site in the before period to a value of 1.0). The reanalysis provided only minor changes in the CMFs and the SDs of the CMFs, suggesting that summing the volumes was an acceptable technique for this evaluation.

Table 8. Results from traffic volume analysis of each site and groups of sites.

Site

Before-Period Crashes

Before-Period Traffic Volume (Vehicle/Day)

After-Period Crashes

After-Period Traffic Volume (Vehicle/Day)

Percent Change in Traffic Volume

CMF

SD of CMF

AL-Plum

168

26,000

40

27,000

3

0.56

0.12

AL-Retail

44

36,000

3

38,000

6

0.15

0.09

NC

200

36,000

159

37,000

3

0.76

0.13

OH-Symmes

113

20,000

70

25,000

25

1.20

0.24

OH-Tylersville

104

20,000

24

17,000

−13

0.64

0.17

OH-Hamilton-Mason

80

12,000

9

17,000

48

0.15

0.05

TX-Evans

103

104,000

325

110,000

6

0.97

0.17

TX-Stone Oak

42

80,000

169

89,000

11

1.16

0.25

TX-New Guibeau

103

68,000

62

83,000

22

0.48

0.10

TX-Shaenfield

81

58,000

82

79,000

36

0.72

0.15

All AL

212

62,000

43

65,000

5

0.47

0.10

All OH

297

50,000

103

59,000

19

0.67

0.12

All TX except TX-71

329

310,000

638

361,000

16

0.98

0.15

AL, NC, and OH

709

148,000

305

161,000

9

0.75

0.12

All except TX-71

1,038

458,000

943

522,000

14

1.09

0.16

AL = Alabama; NC = North Carolina; OH = Ohio; TX = Texas.

Comparison Groups

The primary analysis method in this evaluation used comparison sites to adjust for the possibility of changes during the study period, such as development patterns, significant weather events, driver behavior, vehicle fleets, and crash reporting tendencies. As discussed in the methodology section, the key to a successful comparison site analysis is to find comparison sites that match the crash patterns of the treatment sites year by year in the before period. It is believed that the comparison sites change year by year in the after period, reflecting what would have happened at the treatment sites if the treatment had not been installed.

The project team selected comparison sites using the following criteria:

The project team narrowed the list of potential comparison sites using the time series of aerial photos available via the Internet. This review revealed construction or development at many of the potential comparison sites during the time periods of interest, thus disqualifying those sites from further analysis. The project team consulted with local or State transportation officials responsible for the remaining potential sites to gather additional input on high-quality sites.

Table 9 provides a list of potential comparison sites that met the criteria to warrant the collection of crash data. The before and after periods of crash data collected at all comparison sites were equal to the periods for the corresponding treatment site. There were four potential comparison sites for each treatment site.

Table 9. Potential comparison sites.

RCUT Treatment Site

Potential Comparison Site 1

Potential Comparison Site 2

Potential Comparison Site 3

Potential Comparison Site 4

US-231 NW of Dothan at Plum Rd.

US-231 NW of Dothan at Redmond Rd.

US-231 NW of Dothan at John D. Odom Rd.

US-231 NW of Dothan at University Dr.

US-231 NW of Dothan at County Road 59 and Midtown Ave.

US-231 NW of Dothan at Retail Dr.

US-231 SE of Dothan at Ross Clark Cir.

US-231 NW of Dothan at Murphy Mill Rd.

US-231 NW of Dothan at Napier Field Rd.

US-231 NW of Dothan at North Cherokee Ave.

US-421 south of Piner Rd., Wilmington

US-421 at Sanders Rd., Wilmington

US-421 at Silva Terra Dr., Wilmington

US-421 at Myrtle Grove Rd., Wilmington

US-421 at Sea Breeze, Wilmington

OH-4 at Symmes Rd., Hamilton

OH-4 Dixie Hwy. and Ross Rd. in Fairfield

OH-4 Dixie Hwy. and Seward Rd., Fairfield

OH-4 Port Union Rd., Hamilton

South Gilmore Rd. and Mack Rd., Fairfield

OH-4 at Tylersville Rd., Hamilton

OH-747 Princeton Glendale Rd. and Tylersville Rd., West Chester Twp.

South Ross Rd. and Mack Rd., Fairfield

OH-747 Princeton Glendale Rd. and Union Centre Blvd., West Chester Twp.

OH-747 Princeton Glendale Rd. and Port Union Rialto, West Chester Twp.

OH-4 at Hamilton-Mason Rd., Hamilton

OH-747 Princeton Glendale Rd. and Hamilton-Mason Rd., West Chester Twp.

OH-4 and Hamilton Princeton Rd., Hamilton

OH-4 Hamilton-Middletown Rd. at Indian Meadows Dr., Hamilton

Princeton Rd. and Morris Rd., Hamilton

US-281 and Evans Rd. north of San Antonio

North of San Antonio at Brook Hollow Blvd. and Hemier Rd.

North of San Antonio at Bitters Rd. and Hemier Rd.

North of San Antonio at South Tower Dr. and West Bitters Rd.

North of San Antonio at West Ave. and West Blanco Rd.

US-281 north of San Antonio at Stone Oak Pkwy./TPC Pkwy.

US-281 north of San Antonio at Bulverde Rd.

US-281 north of San Antonio at Overlook Pkwy.

North of San Antonio at TPC Pkwy. and Bulverde Rd.

North of San Antonio at Stone Oak Pkwy. and Canyon Golf Rd.

Loop-1604 west of San Antonio at New Guibeau

TX-16 Bandera Rd. at Tezel Rd. and Prue Rd., San Antonio

NW of San Antonio at Scenic Loop Rd. and Bandera Rd.

NW of San Antonio at Leslie and Bandera

NW of San Antonio at West Hausman Rd. and Babcock Rd.

Loop-1604 west of San Antonio at Shaenfield Rd.

TX-16 Bandera Rd. at Mainland Dr.

Loop-1604 west of San Antonio at Wiseman Blvd.

West of San Antonio at Alamo Pkwy. and Culebra Rd.

Loop-1604 west of San Antonio at Military Dr. West

TX-71, Del Valle, east of Austin at FM-973/Fallwell Ln.

TX-973 at Webberville Rd., Austin

TX-973, Del Valle, east of Austin at Pearce Ln.

TX-973, Del Valle, east of Austin at Burleson Rd.

TX-973 at Clinger Rd., Austin

OH = Ohio; TX = Texas.

The project team employed the odds ratio test, as Hauer described, to determine the best comparison site(s) for each treatment site or group of treatment sites.(5) The odds ratio test measured the change in crash frequency at a comparison site from one year to the next relative to the change in crash frequency at the treatment site. The project team employed the odds ratio test for each available pair of years in the before period at each site and group of sites. Thus, the project team calculated four odds ratios at most at each site, with 5 years of crash data at most in the before period. An odds ratio of 1.0 meant that the comparison and treatment datasets moved together in complete harmony. The project team examined the mean of the odds ratios calculated, as well as the SD of that mean, with desired values of 1.0 for the mean and 0 for the SD. For each individual treatment site, the project team conducted the odds ratio test on each of its potential comparison sites, on potential comparison sites identified for nearby treatment sites, and on each combination of potential comparison sites. The project team used a combination of the best comparison sites found for each individual treatment site for each group of treatment sites.

In this dataset, the project team conducted tests of comparison sites for 9 of the 11 sites where at least 2 years of before-period data were available. They did not test Texas-Evans Road and Texas-Stone Oak comparison sites because only 1 year of before data were available at those sites. Rather, the project team conducted an analysis using all four comparison sites.

Table 10 displays the test results for the best comparison site or sites with each of the nine other treatment sites. To illustrate the quality of the comparison sites, figure 9 and figure 10 show the correspondence between the numbers of crashes per year in the before period at treatment and chosen comparison sites for the Ohio-Symmes site and for the set of all treatment sites, respectively. Most of the nine treatment sites had good to excellent comparison site(s), with means of the odds ratios within 0.1 of 1.0, SDs of the means less than 0.4, and relatively high sample sizes. The sites with the strongest comparison sites included the following:

Note that, at the Alabama-Plum Road site, the best comparison site was from the Retail Drive set of potential sites. This is due to the proximity of those two treatment sites.

Table 10. Comparison site test results.

Site

Parameter

Year 1

Year 2

Year 3

Year 4

Year 5

Mean of Odds Ratio

SD of Mean

AL-Plum

Treat crashes

38

31

19

45

35

--

--

AL-Plum

Comp. crashes

48

46

33

49

52

--

--

AL-Plum

Odds ratio

--

1.12

1.09

0.60

1.30

1.03

0.30

AL-Retail

Treat crashes

13

12

10

6

3

--

--

AL-Retail

Comp. crashes

52

57

55

47

42

--

--

AL-Retail

Odds ratio

--

1.08

1.04

1.20

1.32

1.16

0.13

NC

Treat crashes

44

32

46

38

40

--

--

NC

Comp. crashes

43

46

37

45

61

--

--

NC

Odds ratio

--

1.40

0.54

1.40

1.23

1.14

0.41

OH-Symmes

Treat crashes

24

24

19

24

22

--

--

OH-Symmes

Comp. crashes

29

36

34

48

47

--

--

OH-Symmes

Odds ratio

--

1.15

1.10

1.04

1.00

1.08

0.07

OH-Tylersville

Treat crashes

22

24

16

16

26

--

--

OH-Tylersville

Comp. crashes

31

27

18

23

30

--

--

OH-Tylersville

Odds ratio

--

0.74

0.91

1.14

0.74

0.88

0.19

OH-Hamilton-Mason

Treat crashes

16

12

19

33

--

--

--

OH-Hamilton-Mason

Comp. crashes

17

15

21

20

--

--

--

OH-Hamilton-Mason

Odds ratio

--

1.03

0.79

0.51

--

0.78

0.26

TX-New Guibeau

Treat crashes

52

51

--

--

--

--

--

TX-New Guibeau

Comp. crashes

79

79

--

--

--

--

--

TX-New Guibeau

Odds ratio

--

0.99

--

--

--

0.99

--

TX-Shaenfield

Treat crashes

81

82

--

--

--

--

--

TX-Shaenfield

Comp. crashes

24

13

--

--

--

--

--

TX-Shaenfield

Odds ratio

--

0.81

--

--

--

0.81

--

TX-71

Treat crashes

41

40

30

45

--

--

--

TX-71

Comp. crashes

25

19

18

31

--

--

--

TX-71

Odds ratio

--

0.73

1.16

1.07

--

0.99

0.23

All AL

Treat crashes

51

43

29

51

38

--

--

All AL

Comp. crashes

100

103

88

96

94

--

--

All AL

Odds ratio

--

1.18

1.21

0.60

1.27

1.07

0.31

All OH

Treat crashes

62

60

54

73

48

--

--

All OH

Comp. crashes

77

78

73

91

77

--

--

All OH

Odds ratio

--

1.02

1.01

0.90

1.25

1.04

0.15

All TX

Treat crashes

288

122

30

45

--

--

--

All TX

Comp. crashes

250

111

18

31

--

--

--

All TX

Odds ratio

--

1.04

0.63

1.06

--

0.91

0.24

AL, NC, and OH

Treat crashes

157

135

129

162

126

--

--

AL, NC, and OH

Comp. crashes

220

227

198

232

232

--

--

AL, NC, and OH

Odds ratio

--

1.19

0.90

0.92

1.27

1.07

0.19

All

Treat crashes

445

257

159

207

126

--

--

All

Comp. crashes

470

338

216

263

232

--

--

All

Odds ratio

--

1.24

1.02

0.93

1.43

1.16

0.23

AL = Alabama; NC = North Carolina; OH = Ohio; TX = Texas.
--No data.

Comp. crashes = comparison crashes.

Graph. Crash frequency in the before period for the OH-Symmes treatment site and its recommended comparison sites. Line graph with Year on the x-axis and Number of Crashes on the y-axis. The trend line for comparison sites begins at approximately 28 in Year 1, then 35 in Year 2, 33 in Year 3, 48 in Year 4, and 47 in Year 5. The trend line for treatment sites begins at approximately 25 in Year 1, then 24 in Year 2, 19 in Year 3, 24 in Year 4, and 21 in Year 5.

Source: FHWA.

Figure 9. Graph. Crash frequency in the before period for the Ohio-Symmes treatment site and its recommended comparison sites.

Graph. Crash frequency in the before period for all treatment sites and the recommended set of comparison sites. Line graph with Year on the x-axis and Number of Crashes on the y-axis. The trend line for comparison sites begins at approximately 450 in Year 1, then 325 in Year 2, 200 in Year 3, 240 in Year 4, and 245 in Year 5. The treatment sites’ trend line begins at approximately 400 in Year 1, then 220 in Year 2, 125 in Year 3, 155 in Year 4, and 125 in Year 5.

Source: FHWA.

Figure 10. Graph. Crash frequency in the before period for all treatment sites and the recommended set of comparison sites.

The most important results from the evaluation—the results for all crashes using comparison sites to adjust for potential simultaneous event biases—are shown in table 11. This includes a statistic called Var{w}, which is an intermediate step in the calculation of the CMF and the SD of the CMF.(5) Anyone attempting to replicate the calculations will need Var{w}. For cases in which the Hauer formula suggested a negative value for Var{w}, the project team used a value of 0.0055, which is an intermediate value in the range suggested by Hauer.(5) Table 11 shows that eight sites had CMF values less than 1.0, and three sites had CMF values greater than 1.0. For nine sites, the CMF estimate was more than 1 SD away from 1.0. The group results showed CMF values less than 1.0. The CMF for all sites was 0.85 with an SD of 0.16, so the CMF was less than 1 SD away from 1.

Injury Crashes

The results in table 11 are based on all reported crashes. This subsection provides the results of the analysis on fatal and injury crashes. There were not enough fatal crashes in either the before or after periods to analyze in any detail. In the before period, the following was the fatal crash history at the treatment sites:

There were no fatal crashes at any treatment site after converting it to an RCUT.

The sample of injury crashes was large enough to allow for the same analyses as for all crashes, namely, traffic volume adjustment and comparison site adjustment.

Table 12 contains the results for the analysis of injury crashes adjusting for changes in traffic volume. The analysis again did not use data from the Texas-71 site because no after-period volume data were available. The results are very similar to the results of the traffic volume adjustment analysis on all crash data, with seven sites having a CMF less than 1.0 and two sites having a CMF greater than 1.0. The overall CMF from this analysis was 1.07 with an SD of 0.17.

Table 13 shows the results from odds ratio tests on the best comparison site or sites for each treatment site or group of treatment sites for injury crashes. The odds ratios and SDs were not as strong for injury crashes as all crashes because the sample sizes were smaller. Nonetheless, the odds ratios were mostly at 0.85 or above, and most SDs were below 0.3.

Table 11. Results from comparison site analysis of each site and groups of sites.

Site

Before-Period Treatment Crashes

Before-Period Comp. Crashes

After-Period Treatment Crashes

After-Period Comp. Crashes

Var{w}

CMF

SD of CMF

AL-Plum

168

228

40

104

0.0055

0.51

0.11

AL-Retail

44

253

3

97

0.0055

0.17

0.10

NC

200

232

159

264

0.075

0.64

0.18

OH-Symmes

113

194

70

78

0.0055

1.49

0.31

OH-Tylersville

104

129

24

50

0.0055

0.57

0.16

OH-Hamilton-Mason

80

79

9

17

0.02

0.47

0.20

TX-Evans

103

69

325

175

0.0055

1.20

0.23

TX-Stone Oak

42

53

169

168

0.0055

1.20

0.28

TX-New Guibeau

103

158

62

185

0.0055

0.50

0.10

TX-Shaenfield

81

37

82

49

0.0055

0.72

0.19

TX-71

156

93

16

23

0.0055

0.39

0.13

All AL

212

481

43

201

0.029

0.44

0.11

All OH

297

396

103

199

0.0055

0.98

0.16

All TX

485

410

654

600

0.022

0.88

0.15

AL, NC, and OH

709

1,109

305

664

0.011

0.71

0.09

All

1,194

1,519

959

1,264

0.036

0.85

0.16

Comp. crashes = comparison crashes.; AL = Alabama; NC = North Carolina; OH = Ohio; TX = Texas.

Table 12. Results from traffic volume analysis of each site and groups of sites for injury crashes.

Site

Before-Period Crashes

Before-Period Traffic Volume (Vehicle/Day)

After-Period Crashes

After-Period Traffic Volume (Vehicle/Day)

Percent Change in Traffic Volume

CMF

SD of CMF

AL-Plum

25

26,000

6

27,000

3

0.55

0.25

AL-Retail

8

36,000

1

38,000

6

0.26

0.24

NC

91

36,000

33

37,000

3

0.34

0.08

OH-Symmes

48

20,000

31

25,000

25

1.24

0.32

OH-Tylersville

35

20,000

9

17,000

-13

0.69

0.26

OH-Hamilton-Mason

22

12,000

3

17,000

48

0.17

0.10

TX-Evans

29

104,000

116

110,000

6

1.20

0.28

TX-Stone Oak

17

80,000

61

89,000

11

1.00

0.28

TX-New Guibeau

40

68,000

17

83,000

22

0.33

0.10

TX-Shaenfield

27

58,000

27

79,000

36

0.70

0.20

All AL

33

62,000

7

65,000

5

0.48

0.20

All OH

105

50,000

43

59,000

19

0.78

0.18

All TX (except TX-71)

113

310,000

221

361,000

16

0.98

0.17

AL, NC, and OH

229

148,000

83

161,000

9

0.63

0.12

All (except TX-71)

342

458,000

304

522,000

14

1.07

0.17

AL = Alabama; NC = North Carolina; OH = Ohio; TX = Texas.

Table 13. Comparison site test results for injury crashes.

Site

Parameter

Year 1

Year 2

Year 3

Year 4

Year 5

Mean of Odds Ratio

SD of Mean

AL-Plum

Treat crashes

5

4

4

7

5

--

--

AL-Plum

Comp. crashes

5

4

5

8

6

--

--

AL-Plum

Odds ratio

--

0.69

0.83

0.68

0.79

0.75

0.08

AL-Retail

Treat crashes

4

1

2

1

0

--

--

AL-Retail

Comp. crashes

3

2

3

3

4

--

--

AL-Retail

Odds ratio

--

1.14

0.38

0.86

1.18

0.89

0.37

NC

Treat crashes

21

14

23

17

16

--

--

NC

Comp. crashes

12

9

5

6

7

--

--

NC

Odds ratio

--

0.97

0.29

1.29

1.01

0.89

0.42

OH-Symmes

Treat crashes

9

12

7

11

9

--

--

OH-Symmes

Comp. crashes

4

5

4

9

6

--

--

OH-Symmes

Odds ratio

--

0.70

1.02

1.07

0.67

0.86

0.21

OH-Tylersville

Treat crashes

6

10

9

4

6

--

--

OH-Tylersville

Comp. crashes

24

16

11

12

20

--

--

OH-Tylersville

Odds ratio

--

0.35

0.65

1.83

0.89

0.93

0.64

OH-Hamilton-Mason

Treat crashes

4

3

5

10

--

--

--

OH-Hamilton-Mason

Comp. crashes

11

11

20

16

--

--

--

OH-Hamilton-Mason

Odds ratio

--

0.94

0.85

0.35

--

0.71

0.32

TX-New Guibeau

Treat crashes

19

21

--

--

--

--

--

TX-New Guibeau

Comp. crashes

14

17

--

--

--

--

--

TX-New Guibeau

Odds ratio

--

0.98

--

--

--

0.98

--

TX-Shaenfield

Treat crashes

19

8

--

--

--

--

--

TX-Shaenfield

Comp. crashes

11

5

--

--

--

--

--

TX-Shaenfield

Odds ratio

--

0.89

--

--

--

0.89

--

TX-71

Treat crashes

21

17

10

23

--

--

--

TX-71

Comp. crashes

5

5

3

5

--

--

--

TX-71

Odds ratio

--

0.98

0.79

0.53

--

0.76

0.23

All AL

Treat crashes

9

5

6

8

5

--

--

All AL

Comp. crashes

5

4

5

8

6

--

--

All AL

Odds ratio

--

1.03

0.74

0.91

0.91

0.89

0.12

All OH

Treat crashes

19

25

21

25

15

--

--

All OH

Comp. crashes

39

32

35

37

26

--

--

All OH

Odds ratio

--

0.58

1.21

0.83

1.07

0.92

0.27

All TX

Treat crashes

100

46

10

23

--

--

--

All TX

Comp. crashes

146

27

3

5

--

--

--

All TX

Odds ratio

--

0.39

0.45

0.53

--

0.46

0.07

AL, NC, and OH

Treat crashes

45

43

48

49

36

--

--

AL, NC, and OH

Comp. crashes

56

45

45

51

39

--

--

AL, NC, and OH

Odds ratio

--

0.81

0.86

1.06

0.99

0.93

0.12

All

Treat crashes

149

90

60

73

36

--

--

All

Comp. crashes

205

74

51

59

43

--

--

All

Odds ratio

--

0.59

1.00

0.92

1.42

0.98

0.34

AL = Alabama; NC = North Carolina; OH = Ohio; TX = Texas.
--No data.
Comp. crashes = comparison crashes.

The strongest comparison sites included the following:

Note that, at the Alabama-Plum and Texas-Shaenfield sites, the best comparison sites were from the Retail Drive and New Guibeau sets of potential sites, respectively. This is due to the proximity of those treatment sites to each other.

Table 14 shows the results from the analysis of injury crashes using comparison sites. Note that some of the crash counts for groups of comparison sites do not match the sums of the component individual sites because comparison site data were not double-counted. The CMF values were much like those in the previous table of results, with eight sites having CMF values less than 1.0 and three sites having CMF values greater than 1.0. The CMF for all sites, 0.78, was lower than that for all crashes. This result suggests that signalized RCUTs have a larger positive effect on injury crashes than on property-damage-only crashes. The CMF for injury crashes at all sites was greater than 1 SD from a value of 1.0.

Table 14. Results from comparison site analysis of sites and groups of sites for injury crashes.

Site

Before-Period Treatment Crashes

Before-Period Comp. Crashes

After-Period Treatment Crashes

After-Period Comp. Crashes

Var{w}

CMF

SD of CMF

AL-Plum

25

28

6

13

0.0055

0.45

0.22

AL-Retail

8

15

1

6

0.0055

0.23

0.20

NC

91

39

33

32

0.0055

0.41

0.12

OH-Symmes

48

28

31

8

0.0055

1.90

0.75

OH-Tylersville

35

83

9

32

0.0055

0.62

0.25

OH-Hamilton-Mason

22

58

3

32

0.0055

0.22

0.13

TX-Evans

29

21

116

60

0.0055

1.27

0.39

TX-Stone Oak

17

20

61

56

0.0055

1.13

0.39

TX-New Guibeau

40

31

17

32

0.0055

0.38

0.13

TX-Shaenfield

27

16

27

28

0.0055

0.50

0.19

TX-71

71

18

11

7

0.0055

0.33

0.15

All AL

33

28

7

13

0.0055

0.41

0.19

All OH

105

169

43

72

0.0055

1.06

0.25

All TX

184

106

232

183

0.0055

0.88

0.15

AL, NC, and OH

229

236

83

117

0.0055

0.63

0.11

All

413

357

315

306

0.068

0.78

0.20

Comp. crashes = comparison crashes.; AL = Alabama; NC = North Carolina; OH = Ohio; TX = Texas.

Spatial Patterns

The crash data obtained for this evaluation specified location well enough to allow for a spatial patterns analysis. Notable clusters of crashes included the following:

Thus, with a few exceptions, the crash data mostly showed clusters of rear-end crashes occurring at the RCUT sites. These patterns are somewhat different from those seen at typical conventional intersections, which would tend to feature more prominent clusters of turning and angle crashes.

Other Variables

The collected data allowed for examination of other variables besides severity and location. The appendix provides more information on the changes to crash type, light, weather, road condition, and occasionally other variables (when available) from the before period to the after period at each site. The Alabama-Retail, Ohio-Hamilton-Mason, and Texas-71 sites did not have enough crashes in the after period to detect any important changes. Despite the available data at the Texas-Stone Oak site, no significant changes in the variables occurred at this site. Several important changes occurred at the remaining sites between the before and after periods, including the following:

The most prominent changes with RCUT installation appear to be decreases in angle crashes and increases in sideswipe crashes.

 

 

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