A speed limit compliance model for dynamic speed display sign

• DSDS is an effective temporary solution for speed control within a limited domain.
• Upstream compliance, time and date significantly explained speed limit compliance.
• Lack of full compliance with speed limit does not trivialize DSDS effectiveness.
• DSDS acted as a reminder for slow drivers to raise their speed.
• Bayesian Network can depict causal relationships among speed compliance factors.

IntroductionViolating speed limits is a major cause of motor vehicle crashes. Various techniques have been adopted to ensure that posted speed limits are obeyed by drivers. This study investigates the effect of dynamic speed display signs (DSDSs) on drivers’ compliance with posted speed limit.MethodAn extensive speed data collection upstream of, adjacent to, and downstream of DSDS locations on multiple road classes with different speed limits (25, 35, and 45 mph) was performed short-term and long-term after DSDS installation. Conventional statistical analysis, regression models, and a Bayesian network were developed to assess the DSDS’s effectiveness.Results’ conclusionsGeneral compliance with speed limit (upstream of the DSDS location), time of day, day of week, duration of DSDS operation, and distance from the DSDS location were significantly correlated with speed limit compliance adjacent to the DSDS. While compliance with the speed limit due to the DSDS increased by 5%, speed reduction occurred in 40% of the cases.Practical applicationsSince drivers were likely to increase their speed after passing the DSDS, it should be installed on critical points supplemented with enforcement.