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Publication Number: FHWA-HRT-10-068
Crosswalk Marking Field Visibility Study
CHAPTER 7. CONCLUDING REMARKS
Basic information about crosswalk markings is included in part 3 of the MUTCD. Crosswalk markings are to provide guidance for pedestrians crossing roadways by defining and delineating paths on approaches. The amount of research into the effectiveness of pedestrian treatments has increased in recent years, but there had been insufficient research to identify the relative visibility and driver behavior effects of the many different styles and patterns of crosswalk markings used in the United States and abroad. The lack of knowledge of the relative visibility of different marking patterns has inhibited the development of a consensus on whether more uniformity is needed in the form of tighter MUTCD standards or more comprehensive guidance on crosswalk markings.
The objective of this study was to investigate the relative visibility of three crosswalk marking patterns. These patterns were transverse lines, continental, and bar pairs. In general, this study collected information on the distance from the crosswalk when the participant verbally indicated its presence.
In this study, participants drove an instrumented vehicle on a route through the TAMU west campus. The study vehicles were equipped with instrumentation that allowed the researcher to measure and record various driving performance data. However, the vehicle operated and drove like a normal vehicle. The instrumented vehicle recorded the forward view, and experimenters postprocessed the number of pedestrians and bicyclists in the driver's view at the time when the crosswalk was detected. The route included existing midblock and intersection crosswalk markings along with nine locations where crosswalk markings were installed for this project. Street lighting was present at or near all crosswalk sites, and the new sites were selected to have similar street light levels. The crosswalk markings were installed using white removable retroreflective pavement marking tape. Each of the study sites was located at midblock. The markings were 10 ft in length, selected to reflect a typical length used for midblock crossings. The continental and bar pairs stripes were spaced to avoid the wheel paths of vehicles.
The study was conducted under both daytime (sunny and clear or partly cloudy) and nighttime (with street lights on) conditions over two weeks in November 2009. The following divisions were used in structuring participant recruitment:
A total of 78 participants were included in the study, which exceeded the goal of 64 participants. The original goal was to have 32 participants that were age 55 or older. That goal was exceeded with 35 older participants in the study.
The participant drove the initial portion to become familiar with the vehicle. Once the participant was comfortable in the instrumented vehicle and had arrived in a parking lot near the start of the route, the participant was reminded to indicate when he or she saw one of the following items: crosswalk markings, TWLTL arrows, or a speed-limit sign. The arrows and signs were included to ensure that the driver utilized a normal eye glance pattern and was not exclusively searching for crosswalks. As soon as the driver said "crosswalk," the rear seat experimenter pressed the appropriate button to place a mark in the computer file to indicate detection.
To ensure consistency, the research team used checklists and slide shows to aid in providing instructions to each participant. As part of the in-processing, the participant's and experimenter's response times were measured using a computer test, and a correction factor was developed for each driver to account for the lag between the time the driver verbally responded and the time the experimenter pressed the data recorder button. A more detailed review of the response time data indicated that adjusting the detection distance should occur uniquely for each participant rather than using a per experimenter's average response time. For the nine crosswalks installed for this study, the adjustments to the participant's detection distance ranged between 3 and 13 percent.
After completing the initial route, the participant was given additional instructions and asked to drive the same route again to rate each crosswalk marking on how easy it was to see using a scale of A (excellent) to F (completely unacceptable).
The primary objective of this study was to determine the detection distance of a crosswalk and to identify the variables that affect this distance. The differences in detection distances were evaluated with consideration of the following:
Initially, a statistical model was examined that contained main effects and reasonable two–way interactions (termed the "extended" model). Not all variables could be included in the extended model due to exact linear dependency issues (i.e., a linear combination of one or more factors can exactly duplicate another factor's values). Next, several models were explored to determine the best model to describe the variables that influence detection distance (termed the "reduced" model). Interactions were dropped from the models when the p–value was less than 0.05 (i.e., they were not statistically significant).
Preliminary evaluations demonstrated that the analyses needed to be conducted separately for the study sites (where the markings were installed new at midblock locations) and the existing sites (where the markings were already present at an intersection or midblock with pedestrian warning signs). The preliminary evaluations also clearly showed a difference in detection distance for day and night. Since the nighttime condition had an additional variable (retroreflectivity) to consider and some of the variables were believed to have different effects during the night (such as marking type, vehicle type, and driver eye height), separate analyses were done for daytime and nighttime conditions. In all combinations, daytime detection distances were longer than nighttime detection distances.
For the study sites, the marking type (bar pair, continental, or transverse) was statistically significant. The detection distances to bar pairs and continental markings were similar, and they were statistically different from the detection distance to the transverse markings both during the day and at night.
For the study sites, the presence of traffic had an impact on detection distance, in most cases limiting the ability to see the markings farther upstream, as expected. The impact of traffic on the transverse markings was minimal, as the detection distance to these markings was already small compared to the detection distances for bar pairs or continental. Overall, shorter detection distances were associated with higher operating speeds. However, in most cases it was only slightly shorter detection distances. The characteristics of the streets also influenced the detection of the crosswalk markings. An unexpected result was that the street group with a posted speed limit of 45 mi/h had longer nighttime adjusted detection distances for the higher speeds. This was opposite the finding for daytime conditions; daytime adjusted detection distances were (slightly) shorter for the higher speeds. Variables that included gender, driver eye height, and vehicle type as part of an interaction term were found to be statistically significant; however, closer examination found them to not be of practical significance.
Age (younger versus older) was only a significant factor during the day for the existing sites; however, the size of this difference was quite small and was not considered to be of practical significance. Variables that included gender, driver eye height, and vehicle type as part of an interaction term were found to be statistically significant; however, closer examination found them to not be of practical significance.
For the existing sites, marking type had a significant effect on detection distance during the daytime and the nighttime. There were no existing sites with bar pairs markings, hence only continental and transverse types of markings were compared. During the day, the detection distances to the continental or transverse markings at intersections were not significantly different. The detection distance to midblock continental was statistically different (longer) from the detection distance to midblock transverse markings.
During nighttime conditions at existing sites, variables in addition to marking type had an effect on detection distances, such as location (midblock or intersection) and driver speed. Driver speeds had mixed effects on detection distance depending on location (intersection or midblock) and light level (day or night). For intersections, an increase in driver speed was associated with longer detection distances for both daytime and nighttime conditions. All of the intersections included in this project were either stop–controlled or signal–controlled. Several drivers appeared to be more focused on the stop maneuver than the detection task and would not call out the recognition of a crosswalk until close to the stop bar.
For midblock (or uncontrolled approaches) the finding was dependent on light level. Nighttime detection distance at midblock was similar to intersections; longer detection distances were associated with the higher speeds. For daytime the opposite occurred; higher driver speeds were associated with shorter detection distances at the midblock crosswalks. While the higher driver speeds were associated with shorter detection distances, the differences were small and would not be considered of practical difference.
The conclusions from this project are as follows:
Based on the findings from this research, the researchers recommend revising the MUTCD in the following ways:
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Topics: research, safety, pedestrian, bicycle, pavement markings
Keywords: research, safety, pedestrian, bicycle, crosswalk markings, visibility, continental, transverse, bar pairs, detection distance
TRT Terms: research, infrastructure, safety, road markings, highway facilities for nonmotorized users, pedestrian areas