The effect of advance warning systems on headway distributions in high-speed work zones

In work zone traffic management, warning systems provide road users with real-time traffic conditions through messages or signals. This process aims to adjust driver speeds and headway distribution to affect the smoothness of traffic flow, ultimately achieving safer and more efficient traffic operations. This study examined the distributions of time headways for different vehicle types when traveling upstream of freeway work zones equipped with advanced warning systems. Data were collected through video footage and field observations at two locations on Interstate 80 in Nebraska. Statistical tests were performed to compare headway distributions during periods with active and inactive warning systems. The results indicated that, overall, the activation of the advanced warning systems altered the traffic headway distributions. Specifically: (1) the overall mean headway was significantly smaller under warning conditions compared to no-warning conditions; (2) the mean headway for passenger cars following other vehicles was significantly greater under warning conditions compared to no-warning conditions; and (3) all lead-follow pairs involving a heavy vehicle showed no significant difference in the mean headways with or without activated warning systems. This study also identified the best-fitting distribution models for empirical headways influenced by advanced warning systems. The parametric lognormal distribution and non-parametric Gaussian kernel distribution models were found to provide the best fit, depending on the type of vehicles in lead-follow pairs.