Comparative Study of Short- and Long-Term Urban Freeway Work Zones

Freeway construction and maintenance work in major metropolitan areas is often limited to off-peak daytime or nighttime periods because of the heavy traffic volumes served by these facilities. Previous research has focused primarily on long-term work zones that continuously occupy the road space for several days or months, but little information exists regarding the safety and operational performance of short-term and intermittent sites. The objectives of this study were to compare the accident experience at both long-term and short-term sites before, during, and after freeway construction or maintenance work. In addition, an evaluation of traffic flow and traffic control device (TCD) layout in terms of adherence to state standards was undertaken for both types of zones. It was found that at long-term sites the accident rate increased by an average of 88 percent during the existence of the work zone site, in comparison to the before period, and decreased by an average of 34 percent in the after period. For short-term sites, a nearly constant accident rate of 0.80 accident/ mile-day of construction or maintenance was observed. The evaluation of TCD layout revealed significant discrepancies between standards and practice. In general, devices were placed closer to the lane taper than is allowed by standards. Discrepancies were more frequent at the short-term sites, where an average of two TCDs were missing, in comparison to one TCD missing at long-term sites. Moreover, wider variations in warning signs placement were observed at the short-term sites. Finally, sites characterized by short tapers, missing arrow boards, signs, or any combination of these factors exhibited higher speed variations in the work zone when speed was not dictated by traffic.