Operations and safety of Super 2 corridors with higher volumes.

Project 0-6135As traffic volumes increase, in both urban and rural areas, the demand on the highway network alsoincreases. Specifically, as rural traffic volumes rise in Texas, the pressure on the state\u2019s network of two-lanehighways rises accordingly. Previous research in Texas demonstrated that periodic passing lanes canimprove operations on two-lane highways with average daily traffic (ADT) lower than 5000; these \u201cSuper 2\u201dhighways can provide many of the benefits of a four-lane alignment at a lower cost. This project expands onthat research to develop design guidelines for passing lanes on two-lane highways with higher volumes,investigating the effects of volume, terrain, and heavy vehicles on traffic flow and safety. This reportdiscusses findings from field observations and crash analysis of existing Super 2 highway corridors in Texasand computer modeling of traffic conditions on a simulated Super 2 corridor. Results indicate that passinglanes provide added benefit at higher traffic volumes, reducing crashes, delay, and percent time spentfollowing. Empirical Bayes analysis of crash data reveals a 35 percent reduction in expected nonintersectioninjury crashes. Simulation results indicate that most passing activity takes place within the firstmile of the passing lane, so providing additional passing lanes can offer greater benefit than providing longerpassing lanes. Whether adding new passing lanes or adding length to existing lanes, the incremental benefitdiminishes as additional length is provided and the highway more closely resembles a four-lane alignment.The simulation study also showed that the effects of ADT on operations were more substantial than thee ffects of terrain or truck percentage for the study corridor