Sight-Distance Requirements at Lane-Closure Work Zones on Urban Freeways

Findings of field studies conducted to evaluate the effects of sight distance to lane closures at urban freeway work zones are presented and discussed. The studies investigated the interaction of sight distance with traffic volume and various work-zone traffic-control features (e. g., advance signing and arrowboards). The studies were conducted at 15 maintenance work zones of freeways in Houston, Dallas, Fort Worth, San Antonio, and Corpus Christi, Texas. The studies revealed that, as sight distance to a lane closure decreases, more and more drivers are ” trapped” in the closed lane at the taper area. At sites where the sight distance was less than 1000 ft, for example, up to 80 percent of the traffic in the closed lane did not leave the closed lane until reaching the immediate vicinity of the lane-closure taper. Sight distance becomes even more critical as traffic volumes increase. Based on the study findings, a minimum desirable sight distance of 1500 ft was recommended for lane-closure work zones on freeways. The studies also suggest that advance signing for lane closures is only partly effective. In the studies, only half of the affected drivers responded to the advance signing evaluated. Arrowboards were also studied and proved to be effective traffic-control devices for lane closures where sight distance is adequate, since they encourage early lane changing.