Criteria for Determining Number of Intersections at Divided Highway Junctions

Implementation of proper traffic control at divided highway intersections depends on whether the given junction is considered one intersection or two. The Manual on Uniform Traffic Control Devices (MUTCD) uses median width as the only factor and states that a divided highway junction is treated as two separate intersections if the median is 30 ft or wider. The lack of any documented research for the basis of the 30-ft rule indicates a need to revisit the criterion and reassess its applicability. This study used an analytical approach to evaluate the MUTCD criteria and explored the fundamental issues associated with the function of such a crossing as one or two intersections. The results indicated that the MUTCD definition did not appropriately address the interaction of turning vehicles in a median and that the median width measurement location should be revised. The study also determined that traffic control at divided highway intersections should consider the influence of the median opening length. With the use of the minimum turning paths suggested in the AASHTO Green Book, a set of MUTCD recommendations was developed for determining whether a divided highway junction operates as a single intersection or as two separate intersections. The results of this study indicate that the MUTCD 30-ft rule is an over-simplification and usually an underestimation of the actual requirements to operate a junction as two separate intersections.