Intersection Safety Issue Briefs
Issue Brief 6
Engineering Countermeasures to Reduce Red-Light Running
|Improve Signal Visibility/ Conspicuity||Increase the Likelihood for Stopping||Remove Reasons for Intentional Violations||Eliminate the Need to Stop|
Signal for Each Approach Through Lane. Section 4D.15 of the MUTCD only requires that "a minimum of two signal faces shall be provided for the major movement on the approach..." Under this standard, it would be acceptable to have only two signals on an approach with three or more through lanes. When a signal is positioned such that it is over the middle of the lane, it is in the center of the motorist's cone of vision, thereby increasing its visibility. The additional signal head further increases the likelihood that a motorist will see the signal display for the approach. Placement of a primary signal head over each through lane has been demonstrated to have the lowest incidence of crashes.
Install Backplates. Backplates are used to improve the signal visibility by providing a background around the signals, thereby enhancing the contrast. They are particularly useful in complex visual environments, in eastwest directions, and against bright sky backgrounds, but many agencies use backplates on all signals because of the conspicuity they provide. A retroreflective yellow border strip around the outside perimeter of signal backplates has also been found to significantly reduce nighttime crashes at signals and also helps drivers identify an intersection as signalized during a power failure.
Figure 3: Example of backplates on a multilane arterial intersection
Modify Placement of Signal Heads. Overhead-signal displays help to overcome the three most significant obstacles posed by locations that have only pole-mounted signal heads, which are: (1) they generally do not provide good conspicuity, (2) mounting locations may not provide a display with clear meaning and (3) motorists' line-of-sight blockage to the signal head due to other vehicles, particularly trucks, in the traffic stream. Studies have shown significant reduction in crashes attributed to the replacement of pole-mounted signal heads with overhead-signal heads. However, even with overhead signals, polemounted supplemental signal faces should be considered to further enhance signal visibility and conspicuity.
Increase Size of Signal Displays. 12-inch signal lenses should be considered for all signals, and especially those displaying red indications, to increase signal visibility. The MUTCD requires 12-inch-diameter signal lenses for approaches where speeds are greater than 40 mph and for some other circumstances. Yet many road authorities have made it their policy to use 12-inch-diameter lenses universally for new installations, regardless of the approach speed. Studies in Michigan, North Carolina, and elsewhere have shown the safety benefits of using 12-inch lenses, even in lowspeed situations.
Install Programmable Lens Signals/ Visors or Louvers. Optically programmed or visibility-limited signals limit the field of view of a signal. They allow greater definition and accuracy of the field of view. The MUTCD speaks of visibility-limited signals mostly with regard to left-turning traffic at an intersection. The MUTCD permits the use of visibility limited signal faces in situations where the road user could be misdirected, particularly at skewed or closely-spaced intersections when the road user sees the signal indications intended for other approaches before seeing the signal indications for their own approach. Because the field of view is restricted and requires specific alignment, the signals require rigid mounting instead of suspension on overhead wires. There is some concern associated with glare and the limitations of seeing the signal. Signal visibility alignment requires attention both in design and in field maintenance.
Install LED Signal Lenses. LED units are used for three main reasons: they are very energy efficient, are brighter than incandescent bulbs, and have a longer life increasing the replacement interval. LED signals may be noticeably brighter and more conspicuous than an adjacent signal with the incandescent bulb. LED traffic signal modules have a service life of 6 to 10 years compared to incandescent bulbs that have a life expectancy of only 12 to 15 months. There is a belief that LEDs are brighter and last longer and therefore would provide safety benefits but this has not been quantified. Some studies have found that LED units tend to lose brightness over time instead of exhibiting an immediate failure.
Install Signal Ahead Signs. The MUTCD (Section 2C.29) requires an advance traffic control warning sign when "the primary traffic-control device is not visible from a sufficient distance to permit the road user to respond to the device." In addition to the normal symbolic Signal Ahead warning sign, a sign with the legend BE PREPARED TO STOP (W3-4) can be used.
Install Transverse Rumble Strips. Rumble strips are a series of intermittent, narrow, transverse areas of rough-textured, slightly raised or depressed road surface. The rumble strips provide an audible and a vibrotactile warning to the driver. When coupled with the SIGNAL AHEAD warning sign and also the pavement marking word message – SIGNAL AHEAD –the rumble strips can be effective in alerting drivers of a signal with limited sight distance. There are no known studies reporting on how this treatment can reduce red-light violations or the resulting crashes; hence their use should be restricted to special situations. If used, they should be limited to lower-speed facilities (less than 40 mph) and be reserved for locations where other treatments have not been effective. Rumble strips should not be installed if there will be excessive noise for adjacent residential areas or there are numerous bicyclists using the facility.
Install Activated Advance Warning Flashers. The purpose of an activated advance-warning flasher (AAWF) is to forewarn the driver when a traffic signal on his/her approach is about to change to the yellow and then the red phase. This type of treatment provides a specific warning of an impending traffic signal change ahead. AAWFs inform drivers of the status of a downstream signal. Yellow flashing beacons with the sign are activated or an otherwise blank changeable message such as "Red Signal Ahead" is illuminated for several seconds. The sign and the flashers are placed a certain distance from the stop line as determined by the speed limit on the approach.
Improve Pavement Surface Condition. As a vehicle approaches a signalized intersection and slows to stop for a red light, it may be unable to stop due to poor pavement friction and as a result, proceed into the intersection. Countermeasures to improve skid resistance include asphalt mixture (type and gradation of aggregate as well as asphalt content), pavement overlays, and pavement grooving. Additionally, countermeasures can be considered such as the use of a SLIPPERY WHEN WET sign with a supplemental Advisory Speed Plate for a lower advisory speed.
Adjust Yellow Change Interval. MUTCD (Section 4D.10) provides guidance regarding the duration of yellow change interval. It indicates that the duration of the yellow change interval should be approximately 3 to 6 seconds, with longer intervals reserved for high-speed approaches. The MUTCD does not provide guidance regarding the calculation of clearance interval durations other than to provide ranges of acceptable values. ITE prepared a formula to calculate the yellow change interval that uses a number of operational parameters including perception-reaction time, deceleration rate, approach speed and grade.22
There is a correlation between the duration of the yellow interval and red light running events. Van der Horst observed a substantial reduction in the number of red-light running events after increasing the duration of the yellow interval from 3 to 4 seconds (in urban areas) and from 4 to 5 seconds (in rural areas).23A small adjustment was observed in the drivers' stopping behavior, which was attributed to the relatively low increase in the duration of the yellow interval.24
ITE suggests that a long change interval may encourage drivers to use it as part of the green interval and therefore maximum care should be used when exceeding five seconds. If the calculated or selected yellow change interval length exceeds 5 seconds, it may be the choice of the local jurisdiction to handle the additional time with a red clearance interval. Furthermore, using a yellow change interval length less than 3 seconds may violate driver expectancy and result in frequent entry on red indications. If the interval is too short, rear-end crashes may result.
ITE is in the process of preparing Guidelines for Determining Traffic Signal Change Intervals: a Recommended Practice (RP). In 1985 ITE published a Proposed Recommended Practice titled Determining Vehicle Change Intervals that was not ratified to become an recommended practice. Later, in 2001, ITE published the informational report A History of the Yellow and All-Red Intervals for Traffic Signals.
ITE plans to prepare the RP to reflect the current state-of-the-practice and to provide the user with a broader overview of key considerations to determine yellow change and red clearance intervals for traffic signals and their application. A separate effort is underway by the National Cooperative Highway Research Program (NCHRP Project 03-95) to prepare a document titled Guidelines for Timing Yellow and All-Red Intervals at Traffic Signals. This project will have a longer time horizon because it will incorporate new primary data into the research.
Provide or Adjust All-Red Clearance Interval. An all-red clearance interval is an optional portion of a traffic signal cycle that can follow a yellow change interval and precede the next conflicting green interval. The purpose of the all-red interval is to allow time for vehicles that entered the intersection during the yellow-change interval to clear the intersection before the traffic-signal display for the conflicting approaches turns to green. Engineering formulas should be used to calculate whether this extra clearance interval is needed and what its duration should be based on the speeds, intersection widths and other factors. The all-red clearance interval may also be useful in mitigating the "go" decision by a motorist in the amber dilemma zone when there is not enough time to clear the intersection, particularly at high speed locations. Generally, the duration of the all-red clearance interval is from 0.5 to 3.0 seconds. The MUTCD provides guidance that the all-red clearance interval should not exceed 6 seconds (Section 4D.10).
Adjust Signal Cycle Length. Proper timing of signal-cycle lengths can reduce driver frustration that might result from unjustified short or long cycle lengths. Longer cycle lengths mean fewer cycles per hour and therefore fewer yellow-change intervals per hour and thus can reduce the number of opportunities for traffic-signal violations. On the other hand, signal cycles that are excessively long can encourage RLR because drivers do not want to have to wait several minutes for the next green interval.
Provide Dilemma Zone Protection. The "dilemma zone" has been defined recently to be the area in which it may be difficult for a driver to decide whether to stop or proceed through an intersection at the onset of the yellowsignal indication. It is also referred to as the "option zone" or the "zone of indecision." One potential countermeasure to reduce red-light running is to reduce the likelihood that a vehicle will be in the dilemma zone at the onset of the yellow interval. This can be accomplished by placing vehicle detectors at the dilemma zone. They detect if a car is at the dilemma zone immediately before the onset of the yellow interval. If a vehicle is there, the green interval can be extended so that the vehicle can travel through the dilemma zone and prevent the onset of the yellow while in the dilemma zone.
Coordinate Signal Operation. Interconnected signal systems provide coordination between adjacent signals and are proven to reduce stops, reduce delays, decrease accidents, increase average travel speeds, and decrease emissions. An efficient signal system is also one of the most cost-effective methods for increasing the capacity of a road. With reduced stops, the opportunity to run red lights is also reduced. In addition, if drivers are given the best signal coordination practical, they may not be as compelled to beat or run a red signal.
Remove Unwarranted Signals. If there is a high incidence of RLR violations, this may be because the traffic signal is perceived as being not necessary and does not command the respect of the motoring public. Sometimes signals are installed for reasons that dissipate over time. For instance, traffic volume may decrease due to changing land-use patterns or the creation of alternative routes. The removal of a traffic signal should be based on an engineering study. Factors to be considered are included in ITE's Traffic Control Devices Handbook. If a signal is eliminated, the traffic engineer must continue to monitor the intersection for any potential increase in crashes.
Construct a Roundabout. When a roundabout replaces a signalized intersection, the RLR problem is obviously eliminated. Single-lane roundabouts and other roundabouts have been shown to have significantly less crashes (and less severe crashes) than signalized intersections. Readers should consult NCHRP 572: Roundabouts in the United States25 and FHWA's Roundabouts: An Informational Guide.26
Figure 4: Example of entry to multi-lane roundabout
The following intersection field inspection form sheet is provided and can be downloaded online at http://safety.fhwa.dot.gov/intersection/redlight/tech/fieldinspfrm.cfm.
The field inspection form should be used to identify the extent to which an intersection approach may exhibit traffic operational or engineering design issues that could have an effect on red-light running. A separate field assessment sheet should be completed for each intersection approach. The form shows the types of information that an engineer or an engineering technician should evaluate to determine if a red-light running problem exists at a specific location. Based on the data, the transportation engineering professional can identify if the RLR problems are due to intentional or unintentional (traffic operational or engineering and design) reasons and can suggest engineering countermeasures as a first step prior to consideration of the placement of automated red light cameras at an intersection.
Figure 5: FHWA Intersection Field Inspection Form
FHWA. Field Guide for Inspecting Signalized Intersections to Reduce Red Light Running. FHWASA-05-008. Washington, DC. 2005. http://safety.fhwa.dot.gov/intersection/redlight/tech/fguide_isirlr/ (HTML) http://safety.fhwa.dot.gov/intersection/redlight/tech/fieldinspfrm.cfm. (Field Inspection Form plus downloadable.pdf form)
Federal Highway Administration, National Highway Traffic Safety Administration, Red Light Camera Systems Operational Guidelines, Washington, DC. January 2005.
Red Light Camera Systems Operational Guidelines, January 2005 (HTML) http://safety.fhwa.dot.gov/intersection/redlight/cameras/fhwasa05002/fhwasa05002.pdf .
FHWA, Research, Development, and Technology, Turner-Fairbank Highway Research Center, Association of Selected Intersection Factors with Red-Light Running Crashes, FHWARD-00-112. Washington, DC. 2000. http://www.hsisinfo.org/pdf/00-112.pdf
Institute of Transportation of Engineers. A History of the Yellow and All-Red Intervals for Traffic Signals. Washington, DC: ITE. 2001.
Institute of Transportation Engineers, Making Intersections Safer: A Toolbox of Engineering Countermeasures to Reduce Red-Light Running. An Informational Report. Washington, DC. 2003. http://safety.fhwa.dot.gov/intersection/redlight/cameras/rlr_report/rlrbook.pdf
Texas Transportation Institute. Engineering Countermeasures to Reduce Red-Light Running. Report 4027-2, College Station, TX. August 2002. http://tcd.tamu.edu/Documents/4027-2.pdf
Texas Transportation Institute. Evaluation of Enforcement Issues and Safety Statistics Related to Red Light Running. Research Report 4196-1. College Station, TX. September 2003. http://tcd.tamu.edu/Documents/4196-1.pdf
1 National Committee on Uniform Traffic Laws and Ordinances (NCUTLO). Uniform Vehicle Code. 2000.
2 RITA, John A. Volpe National Transportation Systems Center, Analysis of Red Light Violation Data Collected from Intersections Equipped with Red Light Photo Enforcement Cameras, DOT-VNTSC-NHTSA-05-01. Washington, DC, 2006.
3 Interim Report: NCHRP Project 03-95 Guidelines for Timing Yellow and All-Red Intervals at Signalized Intersection. Prepared by Vanasse Hangen Brustlin for the Transportation Research Board, September 2009.
4 Porter, B.E. and Berry, T.D. A Nationwide Survey of Self-Reported Red Light Running: Measuring Prevalence, Predictors, and Perceived Consequences. Accident Analysis and Prevention, 33, 735-741. 2001.
5 Retting, R.A. et al. Evaluation of Red Light Camera Enforcement in Oxnard, California. Accident Analysis and Prevention, 31, 169-174. 1999.
6 Porter, B.E. and Berry, T.D. 2001.
7 Retting, R. A. and Williams A.F. Characteristics of Red Light Violators: Results of a Field Investigation. Journal of Safety Research, 27(1), 9-15. 1996.
9 Retting, R.A. et al., 1999.
10 Bonneson, et. al. Engineering Countermeasures to Reduce Red-Light-Running. Report No. FHWA/TX-03/4027-2. Texas Department of Transportation, Austin, TX. 2002.
11 Radwan, E. et al. "Red-Light Running and Limited Visibility Due to LTVs Using the UCF Driving Simulator." Orlando, FL: Center for Advanced Transportation Systems Simulation, University of Central Florida, Florida Department of Transportation. 2005.
12 Brewer et al. Engineering Countermeasures to Red-Light-Running. Proceeding of the ITE 2002 Spring Conference and Exhibit (CD-ROM). Washington, DC: Institute of Transportation Engineers. 2002.
13 Retting et al. Red-Light Running and Sensible Countermeasures: Summary of Research Findings. Transportation Research Record 1640, 23-26. Transportation Research Board, Washington, DC. 1998.
14 Lum, K.M. and Wong, Y.D. Impacts of Red Light Camera on Violation Characteristics. Journal of Transportation Engineering, November/December, 648-656. 2003.
15 Porter, B.E. and England, K.J. Predicting Red-Light Running Behavior: A Traffic Study in Three Urban Settings. Journal of Safety Research, 31(1),1-8. 2000.
16 Baguley, C. Running the Red at Signals on High-Speed Roads. Traffic Engineering & Control, 29, 7-8. 1988.
17 Van der Horst, R. and Wilmick A. Drivers' Decision-Making at Signalized Intersections: An Optimization of the Yellow Timing. Traffic Engineering & Control, December, 615-622. 1986.
18 Cesar Quiroga, Edgar Kraus, Ida van Schalkwyk, and James Bonneson, CTS-02/150206-1: Red Light Running, A Policy Review, Texas Transportation Institute, Center for Transportation Safety, March, 2003, Page 4.
19 Van der Horst, R. Driver Decision Making at Traffic Signals. Transportation Research Record 1172, 93-97. 1998.
20 Traffic Engineering Handbook, Washington, DC. ITE. 1999.
21 Making Intersections Safer: A Toolbox of Engineering Countermeasures to Reduce Red-Light Running: An Informational Report, ITE. 2003 http://safety.fhwa.dot.gov/intersection/redlight/cameras/rlr_report//.
22 Determining Vehicle Signal Change and Clearance Intervals, Washington, DC: ITE, 1994.
23 Van der Horst, R. 1998.
24 Cesar Quiroga, Edgar Kraus, Ida van Schalkwyk, and James Bonneson, CTS-02/150206-1: Red Light Running, A Policy Review, Texas Transportation Institute, Center for Transportation Safety, March, 2003, Page 5.
26 Robinson, B. W., L. Rodegerdts, W. Scarbrough, W. Kittelson, R. Troutbeck, W. Brilon, L. Bondzio, K. Courage, M. Kyte, J. Mason, A. Flannery, E. Myers, J. Bunker, and G. Jacquemart. Roundabouts: An Informational Guide. Report FHWA-RD-00-067. FHWA, U.S. Department of Transportation, June 2000. (This document is being updated, with publication likely in 2010.)
Federal Highway Administration
Office of Safety