Road User Impacts Due to Speed Limit Reduction in Work Zones: Which Tool Is Best: Quickzone or Visum?

The Utah Department of Transportation (UDOT) ExpressLink project on I−15 will increase capacity by adding express lanes in each direction from 500 North to I−215 ramp in Davis County, Utah. These express lanes will help ease the commute between Salt Lake County and Davis County. The construction requires planning work zone activities in such a way that user delay costs are minimized. Any lane reduction will increase congestion. So, UDOT instead of closing lanes will reduce both speed limits and lane widths. The paper presents an evaluation of UDOT’s procedures for deriving the user delay costs due to reduced speed limits. UDOT user delay procedures are compared to estimates from two common simulation tools (VISUM and QuickZone (QZ)). The reliability of results from these tools depends upon the type of field conditions assumed. QZ results are reliable when detour traffic conditions are neither available nor assumed in the field due to work zones. VISUM provides accurate estimations, if there are detours. The UDOT’s own procedure delivers results that are commensurate with those from QZ. In contrast, the paper shows how trip assignment modeling, through VISUM, is justified when a network provides drivers with alternate routes and diversionary paths.