Effect of a Pavement Marking Countermeasure on Improving Signalized Intersection Safety

Institute of Transportation Engineers. ITE Journal, Aug 2007 by Yan, Xuedong, Radwan, Essam, Guo, Dahai

IN THIS FEATURE, A PAVEMENT MARKING COUNTERMEASURE IS PROPOSED FOR SIGNALIZED INTERSECTIONS TO ASSIST DRIVERS IN MAKING A CLEAR STOP/GO DECISION AT THE ONSET OF THE YELLOW CHANGE INTERVAL. TO TEST THE EFFECTIVENESS OF THE COUNTERMEASURE, A DRIVING SIMULATOR EXPERIMENT WAS CONDUCTED TO COMPARE DRIVING BEHAVIOR AT INTERSECTIONS WITH AND WITHOUT THE MARKING.

(ProQuest: ... denotes formulae omitted.)

INTRODUCTION

There is a length of roadway on the approach to a signalized intersection where it is difficult for drivers to decide whether to cross or stop at the intersection at the onset of the yellow signal. This region of roadway is commonly referred to as the dilemma zone.1'2

When vehicles are located in the dilemma zone, drivers who decide to proceed through the intersection at the onset of the yellow indication may run a red light, potentially resulting in a right-angle collision. Because of driver behavior variations in the dilemma zone, some drivers may stop abrupdy while others may decide to cross the intersection. This situation may contribute to the risk of a rear-end crash.3

A pavement marking with the word message SIGNAL AHEAD is listed in the Manual on Unifarm Traffic Control Devices (MUTCD) as a warning word marking for signalized intersections to alert drivers to a signal with limited sight distance.4 However, no known studies report on how this treatment can reduce red-light running violations or improve intersection safety.

In diis study, to reduce the dilemma zone and improve traffic safety at signalized intersections, the warning word marking was proposed to assist motorists in stop/go decisions at the onset of the yellow signal change. To test the effect of the pavement marking countermeasure, a driving simulator experiment was conducted to investigate the differences in driver behavior at intersections with and without the marking.

PAVEMENT MARKING COUNTERMEASURE

A pavement marking with the word message SIGNAL AHEAD (see Figure 1) is placed on the pavement of the upstream approach to a signalized intersection and is sufficient to permit vehicles cruising at the speed limit to stop safely before reaching the intersection stop bar. The marking position is related to speed limit and deceleration rate, which is referenced in ITEs Traffic Engineering Handbook? The distance from the marking to the stop bar is calculated by Equation 1:

... (1)

where:

X= distance from the marking to the stop bar (meters [m])

V= 85th-percentile speed or speed limit (m/second)

t = reaction time (1.0 second)

a = average deceleration rate (3.05 m/second^sup 2^)

g = grade of intersection approach

The intent of the marking design is that drivers located upstream of the marking at the onset of the yellow phase are encouraged to stop at the intersection. On the other hand, drivers located downstream of the marking at the onset of the yellow phase are encouraged to cross the intersection. Potentially, the marking provides drivers with relative position information: where they can cross intersections safely. Because the markings have a fixed position at the intersection, drivers who adhere to the speed limit will be more likely to benefit from the marking information.

DRIVING SIMULATOR EXPERIMENT DESIGN

Apparatus

In this study, a high-fidelity driving simulator was used as an experiment tool for data collection. The driving simulator was an I-Sim Mark-II system with a motion base capable of operation with six degrees of freedom. It included five channels (one forward, two side views and two rear-view mirrors) of image generation, an audio and vibration system and steering wheel feedback.

Experimental Design

This experiment utilized within-subjects repeated measures to test the effectiveness of the pavement marking countermeasure. The three treatment factors were speed limit, treatment type and yellow-phase onset distance. There were two levels for speed limits (48.3 kilometers per hour [km/hr.] = 30 miles per hour [mph] and 72.4 km/hr. = 45 mph), two levels of treatment types (with and without marking) and eight yellow-phase onset distances for each speed limit.

The yellow onset distance determines the length from the simulated vehicle to the intersection when drivers encounter a yellow phase intersection. For the 48.3-km/hr. speed limit, the eight levels for yellow onset distances ranged from 25 to 85 m widi 8.57-m increments. For the 72.4-km/hr. speed limit, the eight levels ranged from 55 to 1 10 m with 7.86-m increments. In total, the factorial manipulation of the three factors described above resulted in 32 unique intersection approach types.

Those test intersections with randomly assigned yellow onset distances were along urban streets in a downtown area with 48.3-km/hr. speed limits and along suburban arterials with 72.4-km/hr. speed limits, respectively. Eight driving simulator experimental scenarios were designed for the subject test drive. Four scenarios had the pavement marking; the other four scenarios did not.

Besides the test intersections that displayed signal change, subjects encountered additional signalized intersections. They were intermingled with the test intersections in each scenario and always displayed a continuous green phase. The continuous green intersections were designed to keep subjects from continually expecting a signal change at every intersection.