Guidelines for storage distance between highway-highway and highway-railroad intersections

Abstract

The issue of storage distance at highway-railroad grade crossings is one that has received a great deal of attention over the past few years. Several crashes involving buses and tractor-trailers have prompted the U.S. Department of Transportation to identify storage distance at highway-railroad grade crossings as one of the five safety problem areas that require detailed examination. The primary objective of this research was to develop storage distance recommendations based on a queuing analysis and the analysis of several counties in Texas. The queuing analysis was performed using a theoretical queuing model and a computer simulation model CORSIM. The two models were then compared to field data in order to validate their results. Storage distance distributions were also developed for five counties throughout Texas. Unfortunately, it was determined that the CORSIM results could not be validated due to limitations with its output tables. It was determined that the queuing models utilized for this research are good predictors of queue lengths that occur in the field and can be used as the basis for storage distance guidelines. From these models, queue length values were developed for signalized intersections and unsignalized intersections. These projections allow a designer to estimate a safe storage distance based on projected traffic volumes, signal characteristics, and degree of saturation. These plots also show that relatively normal traffic volumes can cause queue lengths to extend beyond the 200 foot (8 vehicles, each vehicle is assumed to be 25 feet long) distance required for interconnection of railroad and intersection signals. This means that a designer should look into interconnection beyond 200 feet if the volume and signal characteristics warrant a storage distance of more than 200 feet.