What is the effect of in-pavement flashing lights on motorist speeds, yielding behavior, and conflicts with pedestrians?
Many communities are asking about the efficacy of in-roadway flashing warning lights as a safety enhancement at uncontrolled pedestrian crosswalks. An in-roadway warning light system (IRWL) "consists of a series of amber or white lighting units encased in durable housings and embedded in the pavement parallel to a marked crosswalk" (ITE Traffic Engineering Committee TENC-98-03, 2001). The lights typically only display outward in the directions of oncoming traffic and may be activated passively by pedestrians passing through or waiting in a detection area, or actively, by push-buttons.
We reviewed the existing evidence of safety effects of this MUTCD-approved treatment. Nine studies were identified that provided some evaluation of potential safety effects, all using behavioral measures of effectiveness. All of the studies conducted before and after observational studies of driver yielding behaviors; eight provided some assessment of motorist speeds at or near the crosswalks; and several also observed conflicts or pedestrian crossing behaviors. In only two studies were observations conducted at night (clearly under conditions of darkness); no reports mentioned conducting observations under adverse weather conditions. Most of the studies included one treatment site, and none included comparison sites to control for time-related trends or other unknown factors. Although the earliest study included nine treatment locations, there were again, no control sites, no aggregate assessment of treatment effects, and only anecdotal assessment of factors that may have contributed to varied outcomes observed. Confounding treatments and other conditions were also noted in several of the studies. Most of the studies have determined only short-term effects of the treatment, having examined the effects for intervals from a few weeks to several months post-implementation. One study examined effects at one year following implementation at one location (3), and there was a single long-term follow-up of two years at one site (9). A study intended to assess the long-term effects of the treatment near an urban metro station was suspended due to an inability to complete data collection because of system malfunctions.
The following results were noted from the review:
- Short-term improvements in motorist yielding to pedestrians were reported from most sites studied, but no improvement or improvement only to low levels was reported for a number of locations, approaches, or study conditions (2, 3, 4, 9). Whether the variations in results are due to site conditions or study factors cannot be determined.
- Trends (from two studies) were for greater improvements at night-time (7, 9); however effects under other sub-optimal visibility conditions such as rain or fog have not been clearly studied.
- Evidence from several studies does suggest that if motorist yielding is quite low before treatment, the addition of flashing crosswalks alone may be insufficient to bring motorist yielding rates up to a desirably high level (daytime yielding rates remained well below 50%) (2, 3, 4, 9). These results suggest that poorly functioning crosswalks may warrant either different treatments, improvements in addition to IRWL, or reconsideration of the crosswalk location itself, if suitable enhancements cannot be determined.
- There were inconsistent results (between two studies) on whether IRWL improves yielding to pedestrians in the middle of their crossing as when approaching a second travel lane (2, 5). This measure of effectiveness may have a greater bearing on safety than yielding for pedestrians waiting or just beginning to cross, but not yet in the path of vehicles. The effect of IRWL on those in the middle of their crossing, particularly for multi-lane roads should be further studied. In the meantime, caution should be exercised, and perhaps additional treatments implemented if IRWL is considered for uncontrolled crosswalks at multi-lane locations.
- Reported effects on motorist speeds were also mixed with some studies finding improvements or slight improvement in speeds (6, 8, 9); no improvement (3, 9); or mixed results for some locations and study conditions (2, 9). For example, Whitlock and Weinberger found no significant change in speeds at five locations, slight decreases at two locations, and mixed results at one location (9). One study reported significant increases in speeds from before to after treatment (5) and one study did not report results of speed observations. Two studies reported on cases where speeds at one or more locations had initially decreased but at a later time period had tended to rise back toward (2), or even above baseline speeds (1). Differences in speed by approach lane and other traffic conditions that could affect multiple threat risk were also observed in some studies (2, 5). Speed is crucial to motorists' ability or willingness to stop when needed (Garder, 2004). If speeds increase following treatment, collision risk as well as risk of more serious injuries in the event of a collision could increase. The potential also exists for motorists to learn to rely on the lights to indicate presence of pedestrians; if the lights fail to work or are not activated, speeding motorists may be unable to stop in time.
- Effects on conflicts between motorists and pedestrians using the crosswalk also varied, along with the definitions of conflicts used in the studies. Authors reported a non-significant increase in conflicts in one study (6), reduced conflicts at all four locations in a study from Israel (2), reduced conflicts following installation of high visibility crosswalks and sidewalk improvements, but no improvement related to the IRWL in one study (1). Also, fewer conflicts were observed among those using the IRWL crosswalk compared to those crossing at other locations (after period only, 3).
- Proportions of pedestrians using the crosswalk improved at some locations (8), and not at others (2, 3,). The crosswalk location and convenience to desired routes likely has a bearing on whether pedestrians will use the crosswalk in addition to any perceptions of enhanced safety.
- Effects on pedestrian delay have not been well studied and were assessed at only one location. Pedestrian wait time and crossing time did decrease at this location (8).
- Longer-term data are generally lacking. When data were available, improvements in yielding and other measures were typically greatest at the shortest after-interval measured, with worsening trends seen at later time intervals (1, 2, 9). Thus, the potential for a degradation of initial improvements is suggested, and the treatment should be monitored at repeated intervals over a year and longer. Certainly any available crash data and characteristics should be considered.
In summary, motorist yielding to pedestrians improved in the short term to varying degrees at most locations examined. However, yielding may not improve to a sufficiently high degree or may worsen at some locations with poor pedestrian conditions and initial very low yielding rates. The effect of IRWL traffic speeds, on conflicts, and on pedestrian use of the crosswalks, is unclear, and may vary by study conditions or treatment site. Positive effects may also degrade over time as found in several studies. Unfortunately, it is not clear from the evaluation studies reviewed, under what conditions flashing crosswalk treatments may be most beneficial over the longer term, while not recommended for others. Clearly, the location, site conditions and environmental factors should be carefully assessed to determine if this treatment, alone or in combination with other treatments, is the best solution for a particular location. Some communities have removed IRWLs due to both safety and efficiency reasons. If installed, the treatment should be carefully evaluated and monitored long term for effects on pedestrian safety and mobility.
- Boyce, P. and J.V. Derlofske. Pedestrian Crosswalk Safety: Evaluating In-Pavement, Flashing Warning Lights: Final Report. In cooperation with New Jersey Department of Transportation, US Department of Transportation, Federal Highway Administration, March, 2002.
- Van Derlofske, J.F., P. R. Boyce, and C.H. Gilson. (2003). Evaluation of in-pavement, flashing warning lights on pedestrian crosswalk safety. TRB 2003 Annual Meeting: Washington, D.C.
- Hakkert, A.S., V. Gitelman, and E. Ben-Shabat. 2002. An evaluation of crosswalk warning systems: effects on pedestrian and vehicle behavior. Transportation Research Part F (5): 275-292. [retrieved from: http://www.itemltd.com/products/lanelight/resources/ll_xw_ITE2004-InRoadwayLightingPaper.pdf]
- Huang, H., R. Hughes, C. Zegeer, and M. Nitzburg. An Evaluation of the LightGuard Pedestrian Crosswalk Warning System. For Florida Department of Transportation Safety Office, June, 1999. [retrieved from: http://www.dot.state.fl.us/Safety/ped_bike/handbooks_and_research/research/lgresrch.pdf]
- Huang, H. An Evaluation of Flashing Crosswalks in Gainesville and Lakeland. For Florida Department of Transportation, November, 2000. [Retrieved from: http://www.dot.state.fl.us/Safety/ped_bike/handbooks_and_research/research/FLASHXW%20in%20gville%20lakeland.pdf]
- Kannel, E.J. and W. Jansen. In-Pavement Pedestrian Flasher Evaluation: Cedar Rapids, Iowa. Iowa Department of Transportation: Ames, Iowa, April 2004. [Retrieved from http://www.ctre.iastate.edu/reports/ped_flasher.pdf]
- Karkee, G.J., S.S. Nambisan, and S.S. Pulugurtha (2006). An evaluation of the effectiveness of an in-pavement flashing light system. 85th Transportation Research Board Annual Meeting: Washington, D.C.
- Malek, M. Crosswalk enhancement comparison study. Prepared by the City of San Jose Department of Transportation, May 7, 2001.
- Prevedouros, P.D. (2001). Evaluation of in-pavement Flashing Lights on a Six-lane Arterial Pedestrian Crossing. ITE 2001 Annual Meeting and Exhibit: Chicago, IL. [retrieved from http://www.xwalk.com/images/Hawaii_Study.pdf]
- Whitlock and Weinberger Transportation, Inc. An Evaluation of a Crosswalk Warning System Utilizing In-Pavement Flashing Lights. Funding by State of California, Office of Traffic Safety and Federal Highway Administration, through University of North Carolina Highway Safety Research Center, April 1998. [Retrieved from: http://www.w-trans.com/ftp/crosswalk/xwk-report.pdf]
- Garder, P.E. (2004). The impact of speed and other variables on pedestrian safety in Maine. Accident Analysis and Prevention 36: 533-542.
- ITE Traffic Engineering Committee TENC-98-003. In-Roadway Flashing Lights at Crosswalks: an Informational Report. Institute of Transportation Engineers: Washington, D.C., 2001.
The full review and synthesis, provided by Libby Thomas of the UNC Highway Safety Research Center (HSRC), can be found at http://www.walkinginfo.org/library/details.cfm?id=4762.