Safety Effects of the Conversion of Rural Two-Lane Roadways to Four-Lane Roadways. Summary Report

摘要

As traffic increases on a two-lane rural roadway to the point of congested or near-congested conditions, a highway agency is faced with several options: The road can be left with two lanes, ever-increasing congestion, and ever-increasing dissatisfaction among road users; The agency can add short sections of passing lanes to reduce traffic queues; and The two-lane road can be converted to either a four-lane undivided or a four-lane divided facility. The converted roadway will usually follow the same right-of-way and sometimes the same alignment. While a conversion is usually based on the need to more efficiently move increased traffic volumes, it has been assumed that the conversion to the higher order roadway also produces safety benefits. Given the lack of funds for new highway construction and the ever-increasing traffic flows that must be handled in existing roadway corridors, the issue of conversion from two lanes to four lanes is of increasing importance to the State and local transportation departments, the Federal Highway Administration (FHWA), and the public.