Caution: a comment on Alena Erke's red light for red-light cameras? A meta-analysis of the effects of red-light cameras on crashes.

In Red Light for Red-Light Cameras?, Alena Erke concludes that "... on the whole, redlight cameras do not seem to be a successful safety measure." Although Erke's survey of the literature appears to have been comprehensive, her review of the studies was not critical. She appears to have accepted the authors' descriptions of their analyses rather than providing readers with her own considered opinion of how valid those analyses were and what their true implications might be. For the meta-analysis leading to her final conclusion, Erke combines data from two questionable studies with three other "well-controlled" studies. Non-peer-reviewed studies received substantial statistical weight in the meta-analysis. These problems likely produce misleading results. If the highway safety field is to succeed in identifying for policymakers those strategies that are most likely to reduce the human tragedy of motor vehicle crashes, we need first to focus on conducting valid research and analysis. Adding precision to the estimated benefits of those strategies through meta-analysis is important, but secondary, and cannot replace the function of a systematic and critical review.

Crash patterns and potential engineering countermeasures at Maryland roundabouts.

OBJECTIVES: Each year in the United States more than 1.2 million injuries and 9,000 deaths occur in motor vehicle crashes at intersections. Previous research has found that construction of roundabouts in place of traditional intersections can decrease crash frequency and severity. Despite these safety benefits, some crashes still occur at roundabouts. The present study systematically reviewed police crash reports for a set of roundabouts in Maryland to develop a typology of crashes and identify potential countermeasures. METHODS: A total of 283 crash reports were reviewed including 149 crashes at 29 single-lane roundabouts and 134 crashes at 9 double-lane roundabouts. Based on the police reports, crash types were developed and examined by type of roundabout (single-lane, double-lane), crash location within the roundabout (entrance, circular roadway, exit), and other variables. Field observations were conducted at 8 roundabouts with above-average crash histories to aid in identifying potential countermeasures. RESULTS: About three quarters of the crashes involved only property damage. Of the injury crashes, 14% involved at least one disabling injury; the remaining crashes resulted in probable injuries (36%) or nonincapacitating injuries (49%). One common crash pattern at both single- and double-lane roundabouts involved vehicles colliding with the central island, which accounted for almost half of all single-vehicle run-off-road crashes. Other major crash types included rear-end and sideswipe collisions. About three quarters of all collisions occurred at entrances to roundabouts. Based on review of crash reports and visits to several roundabouts, high approach speeds were an important driver crash factor, and some drivers may not have seen the roundabout in time. CONCLUSIONS: Increasing the conspicuity of upcoming roundabouts through larger "roundabout ahead" and "yield" signs could reduce speeds by alerting drivers ahead of time, especially at night. Enhanced landscaping of central islands as well as reflective pavement markers and yield signs at the entrance to roundabouts also could help drivers recognize roundabouts and the need to yield to circulating traffic. Certain design features (e.g., entry deflection on approach roads) also may aid in reducing speeds.

Evaluation of automated speed enforcement in Montgomery County, Maryland.

OBJECTIVES: Almost one quarter of speeding-related fatalities occur on streets with speed limits of 35 mph or less. In 2007, Montgomery County, Maryland, implemented the state's first automated speed enforcement program, with camera use limited to residential streets with speeds limits of 35 mph or less and school zones. The purpose of the present study was to evaluate initial effects of camera enforcement on traffic speeds and to assess public attitudes. METHODS: Vehicle speeds were measured approximately 6 months before and 6 months after speed cameras were deployed and warning signs were installed. Speed data were collected on a sample of roads with and without camera enforcement in Montgomery County, as well as on a sample of roads in a comparison community that did not have speed cameras. In addition, telephone surveys were conducted in Montgomery County. RESULTS: Relative to speeds of drivers on roads in the comparison community, the proportion of drivers in Montgomery County traveling more than 10 mph above posted speed limits declined by about 70% at locations with both warning signs and speed camera enforcement, 39% at locations with warning signs but no speed cameras, and 16% on residential streets with neither warning signs nor speed cameras. Public opinion surveys found 74% of Montgomery County drivers thought speeding on residential streets was a problem. Six months after enforcement began, 60% of drivers were aware of the camera program and 62% supported it. CONCLUSIONS: The camera program was effective at reducing speeding on targeted streets. The finding of speed reductions beyond targeted locations is evidence that highly visible automated enforcement can promote community-wide changes in driver behavior. Although a majority of drivers supported automated speed enforcement, about one third opposed it. Jurisdictions planning to implement speed cameras should draw on international experience to anticipate controversies that generally arise and take steps to address them.

Evaluation of automated speed enforcement on Loop 101 freeway in Scottsdale, Arizona.

Speed cameras can reduce speeding and injury crashes, but in many communities they are confined to low-speed settings such as residential streets and school zones. In 2006 the city of Scottsdale, Arizona, implemented a 9-month pilot program to evaluate the feasibility and effects of highly visible speed camera enforcement on a busy urban freeway. This was the first use of fixed speed cameras on a major US highway. Deployment of six cameras along an 8-mile corridor was associated with large declines in mean speeds and an 88% decrease in the odds of vehicles traveling 11 mph or more above the 65 mph limit. Traffic speeds increased soon after the pilot program was suspended. In addition to reducing speeding along the enforcement corridor, speed cameras were associated with large reductions in speeding on the same highway but 25 miles away from the camera installations. However, traffic speeds were fairly stable on urban freeways in Scottsdale that were not part of the study road. Public opinion surveys found widespread concerns about speeding on the Loop 101 freeway and high levels of support for speed camera enforcement on this road.

Traffic speeds on interstates and freeways 10 years after repeal of national maximum speed limit.

OBJECTIVES: Essentially all published analyses of operational and safety outcomes related to enactment or repeal of the national maximum speed limit (NMSL) were based on data limited to the initial 1-3 years. The purpose of the present study was to collect and analyze longer term speed data. METHOD: In 2006, traffic speeds were surveyed at 26 locations on urban and rural expressways in five states (California, Montana, Nevada, New Mexico, and Texas) where speeds had been measured in 1996, immediately after repeal of NMSL. Most speed limits were unchanged during the approximately 10-year period. However, Montana introduced a numeric 75 mph limit for passenger vehicles in place of a "reasonable and prudent" limit. In Texas, urban freeway speed limits for passenger vehicles were reduced 5 mph, and truck limits were increased 5 mph. RESULTS: On rural interstates without speed limit changes, travel speeds increased for both passenger vehicles and large trucks; the proportion of passenger vehicles exceeding 80 mph tripled. On rural interstates in Montana where speed limits were lowered for passenger vehicles, travel speeds decreased, even for large trucks whose speed limits had not changed. On urban freeways where speed limits did not change, travel speeds declined somewhat for both passenger vehicles and large trucks; during the study period there also were large increases in traffic volume and development of surrounding areas. On urban freeways in Texas where speed limits declined for passenger vehicles, travel speeds generally decreased, even for large trucks whose speed limits actually had increased. CONCLUSIONS: The data suggest that where traffic volumes allow, travel speeds still are increasing 10 years after repeal of NMSL, and many drivers are speeding. The study also shows that speed increases can be curbed and even reversed when speed limits are lowered. Increased enforcement is needed to curb speed increases and the increased risk of serious crashes.

Reducing red light running through longer yellow signal timing and red light camera enforcement: results of a field investigation.

Red light running is estimated to account for 900 intersection crash fatalities annually. Two principal methods used to reduce red light running involve lengthening the duration of yellow change intervals and automated red light enforcement. The present study evaluated the incremental effects on red light running of first lengthening yellow signal timing, followed by the introduction of red light cameras. At six approaches to two intersections in Philadelphia, Pennsylvania, yellow change intervals were increased by about 1s, followed several months later by red light camera enforcement. The number of red light violations was monitored before changes were implemented, several weeks after yellow timing changes were made, and about 1 year after commencement of red light camera enforcement. Similar observations were conducted at three comparison intersections in a neighboring state where red light cameras were not used and yellow timing remained constant. Results showed that yellow timing changes reduced red light violations by 36%. The addition of red light camera enforcement further reduced red light violations by 96% beyond levels achieved by the longer yellow timing. This study shows that the provision of adequate yellow signal timing reduces red light running, but longer yellow timing alone does not eliminate the need for better enforcement, which can be provided effectively by red light cameras.

Characteristics of speeders.

OBJECTIVE: To determine the characteristics of speeders, defined as drivers of vehicles traveling at least 15 mph above the posted speed limit and relatively faster than surrounding vehicles. METHODS: Vehicle speeds were recorded on 13 roads in Virginia with speed limits ranging from 40 to 55 mph. Speeders were compared with slower drivers, defined as drivers of adjacent vehicles traveling no more than 5 mph above the speed limit. License plates were used to identify vehicle owners; owners were inferred to have been driving if observed gender and estimated age matched those of the registered owner. For these drivers, information on exact driver age and gender, vehicle make and model, and driving record was obtained from the Virginia Department of Motor Vehicles. RESULTS: Five percent of the vehicles observed were traveling at least 15 mph above the limit, and 3% qualified as speeders, as defined in this study. Speeders were younger than drivers in the comparison group, drove newer vehicles, and had more speeding violations and other moving violations on their records. They also had 60% more crashes. DISCUSSION: Speeders are a high-risk group. Their speeding behavior is not likely to be controlled without vigorous, consistent enforcement, including the use of automated technology.

Crash reduction following installation of centerline rumble strips on rural two-lane roads.

Rural two-lane roads generally lack physical measures such as wide medians or barriers to separate opposing traffic flows. As a result, a major crash problem on these roads involves vehicles crossing the centerline and either sideswiping or striking the front ends of opposing vehicles. These types of opposing-direction crashes account for about 20% all fatal crashes on rural two-lane roads and result in about 4,500 fatalities annually in the US. The present study evaluated a potential engineering countermeasure for such crashes-installation of rumble strips along the centerlines of undivided rural two-lane roads to alert distracted, fatigued, or speeding motorists whose vehicles are about to cross the centerlines and encroach into opposing traffic lanes. Data were analyzed for approximately 210 miles of treated roads in seven states before and after installation of centerline rumble strips. An empirical Bayes before-after procedure was employed to properly account for regression to the mean while normalizing for differences in traffic volume and other factors between the before and after periods. Overall results indicated significant reductions for all injury crashes combined (14%, 95% confidence interval (95% CI) = 5-23%) as well as for frontal and opposing-direction sideswipe injury crashes (25%, 95% CI = 6-44%)--the primary target of centerline rumble strips. In light of their effectiveness and relatively low installation costs, consideration should be given to installing centerline rumble strips more widely on rural two-lane roads to reduce the risk of frontal and opposing-direction sideswipe crashes.

Types and characteristics of ramp-related motor vehicle crashes on urban interstate roadways in Northern Virginia.

PROBLEM: Freeway entrance and exit ramp interchanges are the sites of far more crashes per mile driven than other segments of interstate highways, but the characteristics and circumstances of ramp crashes have been the subject of relatively little recent research. METHOD: This study examined a sample of 1,150 crashes that occurred on heavily traveled urban interstate ramps in Northern Virginia. Based on a review of diagrams and narrative descriptions from police crash reports, the most common crash types were identified and examined for different roadway locations and ramp designs and by whether at-fault drivers were entering or exiting the freeway. RESULTS: About half of all crashes occurred when at-fault drivers were in the process of exiting interstates, 36% occurred when drivers were entering, and 16% occurred at the midpoints of access roads or on ramps connecting two interstate freeways. Three major crash types--run-off-road, rear-end, and sideswipe/cutoff--accounted for 95% of crashes in the study. The crash type most frequently associated with exiting was run-off-road, and the types most common with entering drivers were rear-end or sideswipe/cutoff. Crashes most common on ramps--run-off-road crashes--frequently occurred when vehicles were exiting interstates at night, in bad weather, or on curved portions of ramps. Speed was often a factor. Crashes occurring on ramp margins (where ramps or access roads enter or exit) were most commonly of the sideswipe/cutoff type. These often involved at-fault passenger vehicles merging from entrance ramps into the sides of large trucks already on the freeway. The predominant crash type on access roads was rear-end crashes; congestion was a factor in these crashes. Alcohol was a reported factor in a sizeable proportion of run-off-road crashes occurring on ramps (14%) and ramp margins (30%). IMPACT ON INDUSTRY: Candidate countermeasures for run-off-road crashes include geometric design changes to increase ramp design speed such as increasing curve radii. Speed-related crashes may be reduced by the use of speed cameras accompanied by publicity. Rear-end crash countermeasures could include surveillance systems that quickly detect unexpected congestion, incident response programs, and variable message signs to alert drivers to traffic congestion ahead. Countermeasures for sideswipe/cutoff crashes could include extending the length of acceleration lanes.

Effects of red light cameras on violations and crashes: a review of the international literature.

Red light running is a frequent cause of motor vehicle crashes and injuries. A primary countermeasure for red light running crashes is police traffic enforcement. In recent years, many police agencies have begun using automated red light cameras as a supplement to conventional enforcement methods. The present study reviewed and evaluated available evidence in the international literature regarding the effectiveness of cameras to reduce both red light violations and crashes. Camera enforcement generally reduces violations by an estimated 40-50%. In terms of crash effects, most studies contain methodological flaws that, to varying degrees, either overestimate (failure to adjust for regression to the mean) or underestimate (comparison with nearby signalized intersections affected by cameras) crash effects. Mindful of these limitations, the research generally indicates that camera enforcement can significantly reduce injury crashes at signalized intersections, in particular right-angle injury crashes. Most studies reported increases in rear-end crashes following camera installation. Taken together the studies indicate that, overall, injury crashes, including rear-end collisions, were reduced by 25-30% as a result of camera enforcement.

A review of evidence-based traffic engineering measures designed to reduce pedestrian-motor vehicle crashes.

We provide a brief critical review and assessment of engineering modifications to the built environment that can reduce the risk of pedestrian injuries. In our review, we used the Transportation Research Information Services database to conduct a search for studies on engineering countermeasures documented in the scientific literature. We classified countermeasures into 3 categories-speed control, separation of pedestrians from vehicles, and measures that increase the visibility and conspicuity of pedestrians. We determined the measures and settings with the greatest potential for crash prevention. Our review, which emphasized inclusion of studies with adequate methodological designs, showed that modification of the built environment can substantially reduce the risk of pedestrian-vehicle crashes.

Analysis of motor-vehicle crashes at stop signs in four US cities.

PROBLEM: Nearly 700000 police-reported motor vehicle crashes occur annually at stop signs, and approximately one-third of these crashes involve injuries. The purpose of this study was to develop a better understanding of the crashes that occur at stop signs and to identify potential countermeasures. METHOD: Police reports of crashes at stop sign-controlled intersections during 1996-2000 in four U.S. cities were examined in detail. At total of 1788 crash reports for intersections with two-way stop signs were included in the study. RESULTS: Stop sign violations accounted for about 70% of all crashes. Typically these crashes were angular collisions. Among crashes not involving stop violations, rear-end crashes were most common, accounting for about 12% of all crashes. Stop sign violation crashes were classified into several subtypes - driver stopped, driver did not stop, snow/wet/ice, and other/unknown. In about two-thirds of stop sign violation crashes, drivers said they had first come to a stop. In these cases, inability or failure to see approaching traffic often was cited as the cause of the crash. Drivers younger than 18 as well as drivers 65 and older were disproportionately found to be at fault in crashes at stop signs. IMPACT ON INDUSTRY: Potential countermeasures include changing traffic control and intersection design, improving intersection sight distance, and increasing conspicuity of stop signs through supplemental pavement markings and other devices.

Reductions in injury crashes associated with red light camera enforcement in oxnard, california.

OBJECTIVES: This study estimated the impact of red light camera enforcement on motor vehicle crashes in one of the first US communities to employ such cameras-Oxnard, California. METHODS: Crash data were analyzed for Oxnard and for 3 comparison cities. Changes in crash frequencies were compared for Oxnard and control cities and for signalized and nonsignalized intersections by means of a generalized linear regression model. RESULTS: Overall, crashes at signalized intersections throughout Oxnard were reduced by 7% and injury crashes were reduced by 29%. Right-angle crashes, those most associated with red light violations, were reduced by 32%; right-angle crashes involving injuries were reduced by 68%. CONCLUSIONS: Because red light cameras can be a permanent component of the transportation infrastructure, crash reductions attributed to camera enforcement should be sustainable.

Changes in crash risk following re-timing of traffic signal change intervals.

More than I million motor vehicle crashes occur annually at signalized intersections in the USA. The principal method used to prevent crashes associated with routine changes in signal indications is employment of a traffic signal change interval--a brief yellow and all-red period that follows the green indication. No universal practice exists for selecting the duration of change intervals, and little is known about the influence of the duration of the change interval on crash risk. The purpose of this study was to estimate potential crash effects of modifying the duration of traffic signal change intervals to conform with values associated with a proposed recommended practice published by the Institute of Transportation Engineers. A sample of 122 intersections was identified and randomly assigned to experimental and control groups. Of 51 eligible experimental sites, 40 (78%) needed signal timing changes. For the 3-year period following implementation of signal timing changes, there was an 8% reduction in reportable crashes at experimental sites relative to those occurring at control sites (P = 0.08). For injury crashes, a 12% reduction at experimental sites relative to those occurring at control sites was found (P = 0.03). Pedestrian and bicycle crashes at experimental sites decreased 37% (P = 0.03) relative to controls. Given these results and the relatively low cost of re-timing traffic signals, modifying the duration of traffic signal change intervals to conform with values associated with the Institute of Transportation Engineers' proposed recommended practice should be strongly considered by transportation agencies to reduce the frequency of urban motor vehicle crashes.