Long-Term Effectiveness of Speed Monitoring Displays in Work Zones on Rural Interstate Highways

The long-term effectiveness of speed monitoring displays (SMDs) was evaluated as part of the Midwest States Smart Work Zone Deployment Initiative, a pooled-fund study sponsored by Iowa, Kansas, Missouri, Nebraska, and FHWA. Three SMDs were deployed for a 5-week period along a 4.35-km (2.7-mile) section between two work zones on I-80 near Lincoln, Nebraska. The mean, 85th percentile, and standard deviation of vehicle speeds and the percentage of vehicles complying with the 89-km/h (55-mph) speed limit and the 97 and 105-km/h (60 and 65-mph) speed thresholds were used as measures of effectiveness (MOEs). The SMDs were found to be effective in lowering speeds, increasing the uniformity of speeds, and increasing speed-limit compliance over the 5-week period. Statistically significant improvements in speed parameters and speed-limit compliance were observed at the measurement points downstream of the first two SMDs. The improvement in standard deviation and some compliance percentages were not statistically significant at the third SMD. Greater speed reductions and compliance increases were observed for passenger cars than for other vehicles. The combined longterm effect of the three SMDs was also assessed using spatially aggregated MOEs. Statistically significant improvement was found in terms of both speed reduction and speed-limit compliance. One week after the removal of the SMDs, there were still statistically significant speed reductions and compliance increases, although they were less than during the deployment.