FHWA-SA-09-014

This case study is one in a series documenting successful 

intersection safety treatments and the crash reductions that 

were experienced. Traffic engineers and other transportation 

professionals can use the information contained in this case 

study to answer the following questions:

•	 Whataresomelow-cost treatmentoptions that can reduceangleand

total crashesat signalizedintersections in urban areas?

•	 How manycrashesdidthetreatments reduce?

•	 Arethereanyimplementation issuesassociated with these

treatments,andif so, how can theybeovercome?

Improving Safety by 

Providing All-Red 

Clearance Intervals and 

Larger Signal Lenses

Photo by April Armstrong (used with permission).

Intersection Safety Case Study
2 FHWA | Improving Safety by Providing All-Red Clearance Intervals and Larger Signal Lenses

Adding or extending an all-red clearance interval (a brief 

period when lights in all directions are red) provides 

additional time before conflicting traffic is released following 

the yellow-change interval. This short all-red clearance 

interval provides a greater time separation between 

opposing vehicular movements, clearing the intersection 

of vehicles between signal phases, thereby reducing the 

potential for a crash. 

Larger signal lenses make traffic signals more visible and provide motorists with more time to determine and respond 

to the color indication. Figure 1 provides a visual comparison of the 8-inch and larger 12-inch traffic signals. Agencies 

can use different sizes of signal lenses in the same signal face or signal head, as specified in the MUTCD Section 4D.15. 

In this case, the cities increased the lens size of all three lenses in the traffic signals for maximum conspicuity.

Objective

The following case study showcases two successful low-cost strategies that measurably improved safety at 33 signalized 

intersections in Detroit and Highland Park, MI. The treatments included providing an all-red clearance interval and 

increasing the size of the signal lens for the red, yellow and green indications. 

Introduction

Red-light running is one of the most serious traffic safety problems facing Americans today. 

It is estimated that vehicles running red lights cause more than 200,000 crashes, 170,000 

injuries and approximately 900 deaths per year1

. Some of these crashes occur because 

drivers are speeding or are distracted, other drivers may be unaware they are approaching 

an intersection, or they are unable to see the traffic control device in time to comply. 

Clearance intervals—both lengthening yellow-change intervals as well as providing an 

all-red clearance interval—together with increasing the size of signal lenses, have been 

shown to improve intersection safety. Increasing the length of the yellow-change interval 

in accordance with the recommended Institute for Transportation Engineers (ITE) formula 

has been shown to significantly decrease the chance of red-signal violations. Providing 

red clearance intervals and increasing the yellow-change interval have been shown to 

decrease late exits from intersections[7].

Treatment Summary

All of the intersection examples used in this report are from 

a corridor that extends between Detroit and Highland 

Park, MI. This case study examines the application of two 

treatment enhancements that reduced angle and injury 

crashes at signalized intersections:

•	 Implementation of all-red clearance intervals ranging from

1.0 to 2.0 seconds2.

•	 Larger (12-inch) signal lenses (red, yellow and green) to

replace 8-inch signal lenses3

.

Figure 1: Relative size difference between 12-inch (top lens) 

and 8-inch signal lens (bottom lenses)

Photo from KLS (used with permission).
FHWA | Improving Safety by Providing All-Red Clearance Intervals and Larger Signal Lenses 3

“The intersection safety 

improvements (which 

included larger signal heads 

and implementing the all-red 

clearance interval) showed 

a great reduction in injury and 

fatal crashes and also ultimately 

helped protect people of all 

ages. Michigan’s experience 

demonstrates the benefits derived 

from a comprehensive approach 

to intersection safety.”

Robert Lariviere 

Traffic Engineer, American Automobile 

Association (AAA) of Michigan

1 Federal Highway Administration Office of Safety Red-Light Running web site (http://safety.fhwa.dot.gov/intersection/redlight).

2 Calculated using Institute of Transportation Engineers (ITE) recommended guidelines ARI = (W+L)/V, where ARI is the length of the all-red interval in seconds, 

W is the intersection width (in feet), L is the length of the clearing vehicle (typically 20 feet), and V is the approach speed (in feet/second).

3 The signal lenses in some of the study intersections were also relocated to improve visibility.

Photo by April Armstrong (used with permission).
4 FHWA | Improving Safety by Providing All-Red Clearance Intervals and Larger Signal Lenses

Results

Problem: The signalized intersections along the 

Woodward Avenue corridor (Route 1) which runs 

between Detroit and Highland Park, MI, were 

experiencing a high number of angle crashes, as well 

as a high number of total crashes. 

Solution: In 1996, the American Automobile 

Association (AAA) of Michigan, in partnership with 

the cities of Detroit and Highland Park, initiated the 

Road Improvement Demonstration Program (RIDP) 

to improve intersection safety along this arterial 

corridor. The program’s main purpose was to identify 

high-crash locations in these cities and develop and 

implement safety measures.

The cities decided to add an all-red clearance interval 

and increase the size of the signal lens for the red, 

yellow and green signals at the intersections along 

the Woodward Avenue corridor. The corridor is 

approximately 7.5 miles long (see Figure 2) with a 

posted speed limit that varies between 35 to 40 miles 

per hour (mph). The corridor consists of three to four 

lanes in the north- and south-bound directions and a 

center lane for left turns.

The safety treatments implemented along the 

Woodward Avenue corridor reduced the targeted 

angle crashes as well as total crashes. After 

implementation of these countermeasures, 90.9 

percent of the treated intersections experienced a 

reduction in angle crashes, 81.8 percent experienced 

a reduction in injury crashes, and 75.8 percent 

experienced reductions in total crashes. At the 

corridor level, the safety treatments had a 

positive effect in reducing the targeted angle 

crashes by 75.7 percent, injury crashes by 45.5 

percent, and total crashes by 33.3 percent 

per year. See Table 1 for a more detailed tabular 

summary of these treatments.

Evaluation Methodology

This case study examines 33 intersections in Detroit and Highland Park, MI with a high incidence of angle crashes 

(many with injuries). Crash reductions were based on a review of “before and after” data from these intersections during 

a minimum of 13 months, between 1997—20024. (The “before” and “after” observation periods ranged between 13-34 

months depending on the intersection). The safety improvements were implemented in 1997.

Figure 2: Site Map of the Woodward Avenue Corridor 

4 Note that crash reduction averages in this report reflect the percent reduction per year based on the difference between the total number of “before” and “after” crashes. 
Locations along 

Woodward Avenue 

corridor

Months

Annual

Months

Average

Total CrashesAnnual AverageAnnualTotal Crashes

Average

Injury CrashesAnnual AverageInjury CrashesAnnual AverageAngle CrashesAnnual AverageAngle Crashes

Sibley/Adelaide Street

Charlotte Street

Eliot/Stimson Street

Mack Avenue

Parsons Street

Alexandrine Street

Canfield Street

Forest Avenue

Warren Avenue

Putnam Street

Kirby Street

Palmer Street

Antionette/Medbury Street

Baltimore Street

Milwaukee Street

Bethune Street

Seward/Marston Street

Euclid Street

Hazelwood/Holbrook St

Clairmount/ Owen Street

Chicago/Aden Park Blvd

Calvert/Trowbridge Street

Tuxedo/ Tennyson Street

Courtland Street

Glendale/McLean Street

Buena Vista Street

Gerald Street

Manchester Street

Sears/Ford Street

Ferris/Pilgrim Street

Merrill Plaisance Street

SevenMile Road

State Fair Avenue

1.0

5.5

2.0

19.0

4.0

14.5

14.0

29.0

51.0

16.0

13.0

13.5

3.5

12.5

24.0

6.5

8.5

14.0

10.5

16.0

12.0

8.5

1.0

1.0

15.0

4.0

2.0

38.0

20.0

9.0

6.5

46.0

28.5

0.0

1.5

0.0

4.0

0.5

2.5

3.5

5.5

11.0

3.0

4.5

2.5

1.5

4.0

7.0

2.0

3.0

4.5

2.5

6.0

4.5

1.0

0.0

0.0

4.0

1.0

1.0

17.0

10.0

2.0

3.5

15.5

9.0

0.0

0.0

0.0

5.5

0.0

1.5

3.5

14

11.5

0.0

0.5

4.0

1.5

0.5

12.0

2.0

1.0

2.0

2.5

6.5

2.0

1.5

0.0

1.0

1.0

1.0

0.0

18.0

4.0

3.0

3.5

8.5

4.0

34

34

34

34

34

34

34

34

34

34

34

34

34

34

34

34

34

34

34

34

34

34

24

24

24

24

24

24

24

24

13

13

13

2.5

2.1

1.4

25.8

5.6

11.6

7.8

18.0

38.5

9.5

5.6

8.8

1.1

7.8

10.2

6.0

6.0

6.7

7.4

7.4

3.9

4.2

2.5

1.5

21.0

7.0

6.0

17.5

11.0

8.0

0.9

24.0

15.7

1.1

0.7

0.4

5.6

1.4

1.4

1.4

3.9

7.8

0.4

0.7

1.8

1.1

1.8

2.1

2.1

1.4

1.1

2.5

1.8

0.0

0.7

0.0

0.0

7.0

3.0

0.5

6.0

5.0

2.0

0.0

6.5

3.7

0.4

0.0

0.4

2.8

0.4

0.7

0.7

1.4

6.0

0.0

0.0

1.4

0.4

0.0

0.7

0.0

0.4

0.7

1.8

0.4

0.4

0.0

0.0

0.5

1.0

0.5

0.0

2.0

1.0

0.5

0.0

3.7

0.0

-150.0

61.8

30.0

-35.8

-40.0

20.0

44.3

37.9

24.5

40.6

56.9

34.8

68.6

37.6

57.5

7.7

29.4

52.1

29.5

53.8

67.5

50.6

-150.0

-50.0

-40.0

-75.0

-200.0

53.9

45.0

11.1

86.2

47.8

44.9

-110.0

53.3

-40.0

-40.0

-180.0

44.0

60.0

29.1

29.1

86.7

84.4

28.0

26.7

55.0

70.0

-5.0

53.3

75.6

0.0

70.0

100.0

30.0

0.0

0.0

-75.0

-200.0

50.0

64.7

50.0

0.0

100.0

58.1

58.9

-40.0

0.0

-40.0

49.1

-40.0

53.3

80.0

90.0

47.8

0.0

100.0

65.0

73.3

100.0

94.2

100.0

60.0

65.0

28.0

93.8

80.0

100.0

0.0

50.0

0.0

50.0

0.0

88.9

75.0

83.3

100.0

56.5

100.0

TOTAL 792 469.5 137.5 116 979 313 74.9 28.2 33.3 45.5 75.7 Total Crashes Injury Angle Crashes Crashes

24

24

24

24

24

24

24

24

24

24

24

24

24

24

24

24

24

24

24

24

24

24

24

24

24

24

24

24

24

24

24

24

24

Percent Reduction 

In Crashes/Year (Injuries/Year) Before After

Table 1: Summary of crash reductions after addition of all-red clearance intervasls and larger signal lenses

FHWA | Improving Safety by Providing All-Red Clearance Intervals and Larger Signal Lenses 5
Discussion

Implementation Issues

The city experienced no implementation issues with 

these countermeasures. 

Cost

The cost to implement the safety improvements at 

all 33 intersections totaled $2.3 million (an average 

cost of $70,000 per intersection). Costs included 

replacement of the smaller (8-inch) signal lens with 

the larger (12-inch) lens, and providing the all-red 

clearance intervals.

Time Frame

The treatments were installed at all locations within 

six months. This included development of retiming 

plans, addition of all-red clearance intervals, and 

installation of the larger 12-inch signal lenses.

Effectiveness 

The combinations of enhanced treatments discussed 

have been effective in reducing crashes at these 

signalized intersections. AAA Michigan conducted a 

benefit-cost evaluation using National Safety Council 

(NSC) cost data and further determined the benefitcost ratio of 11:1 for the specified treatments[4]. 

An Empirical Bayes analysis was also performed 

at selected intersections in the City of Detroit for 

which suitable control sites were identified. Finally, 

the significant results of additional tests (Poisson, 

Chi-Square, and Paired t-tests) conducted by the 

study team helped to further conclude that the 

implemented countermeasures were effective 

in reducing the targeted crashes at a 95 percent 

confidence interval. These results are consistent with 

other similar studies of the effectiveness of these 

treatments.

Summary of Results

The safety enhancements discussed in this case study 

were added to reduce angle and total crashes. The 

combinations of enhanced countermeasures 

installed in these Michigan signalized intersections 

cumulatively reduced angle crashes at the treated 

intersections by 75.7 percent, injury crashes by 45.5 

percent, and total crashes by 33.3 percent. The average 

reductions in crashes achieved by the treatments are 

within the range of crash reductions for these treatments 

(15 percent for all-red clearance interval and 24 percent 

for 12-inch signal lenses for total crashes) mentioned 

in the Desktop Reference for Crash Reduction Factors 

(September 2007), published by the United States 

Department of Transportation (USDOT) Federal Highway 

Administration (FHWA)[2]. 

6 FHWA | Improving Safety by Providing All-Red Clearance Intervals and Larger Signal Lenses
FHWA | Improving Safety by Providing All-Red Clearance Intervals and Larger Signal Lenses 7

References

1) Federal Highway Administration Office of Safety Red-Light 

Running web site (http://safety.fhwa.dot.gov/intersection/

redlight).

2) Desktop Reference for Crash Reduction Factors, FHWASA-07-015, Federal Highway Administration, (Washington, 

DC: September 2007), p. 8, 15. 

3) “Evaluating Impact on Safety of Improved Signal Visibility 

at Urban Signalized Intersections,” Transportation Research 

Record, Transportation Research Board, The National 

Academies, 0361-1981, volume 2019, pp. 51-56, 2007.

4) Datta T.K. and Schattler K.L., Evaluation Studies for the AAA 

Road Improvement Demonstration Program, Wayne State 

University, Michigan, 2003.

5) Polanis, Stanley F., “Improving Intersections Safety through 

Design and Operations (Examples),” presented at ITE 2002 

Spring Conference, Palm Harbor, FL, March 2002.

6) Schattler K.L. and Hill, C. L., “Change and Clearance 

Interval Design on Red-Light Running and Late Exits,” 

Transportation Research Record, pp. 193-201, January 2003.

7) Making Intersections Safer: A Toolbox of Engineering 

Countermeasures to Reduce Red-Light Running: An 

Informational Report. Countermeasures to Reduce Red-Light 

Running, Federal Highway Administration and Institute of 

Transportation Engineers, 2003. 

(http://safety.fhwa.dot.gov/intersection/redlight/rlr_report)

8) SEMCOG Traffic Safety Manual, Southeast Michigan 

Council of Governments, Third edition, 1998.
FHWA-SA-09-014 February 2010

For More Information

Ed Rice

Intersection Safety Team Leader, 

FHWA Office of Safety

202.366.9064

ed.rice@dot.gov

Tapan K. Datta, Ph.D., P.E.

Professor, Civil and Environmental Engineering, 

Wayne State University-Transportation Research Group

313.577.9154

tdatta@eng.wayne.edu

Visit FHWA’s intersection safety web site to download this and 

other case studies highlighting proven intersection safety 

treatments from across the country:

http://safety.fhwa.dot.gov/intersection