Effectiveness of Dynamic Speed Display Signs (DSDS) in Permanent Applications (0-4475-S)

Dynamic speed display signs (DSDSs) reduce vehicle speeds in workzones and other temporary situations. Do such signs reduce speeds if installed permanently at critical roadway locations, as shown above? Can these speed reductions, if they occur, be maintained over significant periods of time? Those are the questions that Texas Transportation Institute (TT]) researchers were asked to answer. According to the results of a recent research study, the answer to both questions is yes, but only incertain situations. What We Did...Texas Department of Transportation (TxDOT) personnel identified several test sites to try out permanently installed DSDSs. TTI researchers conducted field studies to determine whether the signs reduced speeds at each site. Researchers also examined whether the signs increased vehicle conflicts or other types of erratic maneuvers. DSDSs were installed at four common types of roadway situations where excessive speeds can be a significant safety or operational problem: - at the beginning of regulatory school speed limit zones that are active only during the times when students are arriving or leaving school, - at speed zones installed upstream of a schoo lspeed zone (to transition motorists down to the school zone speed limit), - upstream of high-speed signalized intersections,and - upstream of sharp horizontal curves. To evaluate the effect of the permanently installed DSDSs, TTI researchers conducted three field studies at each test location. The first study was performed before installing the DSDS in order to establish baseline trends in traffic speeds and erratic maneuvers. TTI researchers then returned to each test location and collected speed and erratic maneuver data about one week after the DSDS was installed to determine what immediate impact the DSDS had upon traffic behavior at the site.