I Efficiencyof Dual Lefi - Turn lane Intersections In Charlotte : A Study UsingTRAFhE 1 ’ ’ SlM

As traffic volumes increase on major intersecting arterials, the transportation engineer’s challenge is one of optimizing through traffic while providing adequate opportunities for leftturning vehicles. Increasing traffic volumes not only provide a proportionately higher number of leftturning vehicles, but also make it more difficult to negotiate a left turn due to increased opposing traffic. The dual left-turn lane was developed to ease congestion at intersections and to add capacity. The dual left-turn lane allows two lanes of vehicles to turn left simultaneously during a green protected-left signal phase, which would otherwise be used by a single left-turn lane of traffic. Dual left-turn movements can effectively accommodate large volumes of left-turn traffic. Properly applied, this traffic control technique can decrease total intersection delay by providing more green time for other movements through the intersection and increasing overall intersection capacity. Dual left-turn lanes have been in use for more than 30 years. The increased use of dual left-turn lanes in Charlotte, N. C., began in the 1980s. The increased use of these lanes in North Carolina probably is the result of the continued growth of metropolitan areas in the state and the corresponding increase in traffic demands on the street and highway systems. Many cities have minor arterials located approximately at half-mile intervals between the major arterials; however, the street patterns in Charlotte rarely have these intermediate minor arterials. The lack of the minor arterials increases the demand for turning movements at the intersections of the major arterial streets. As turning movement volumes increase, one design alternative is to utilize a dual rather than a single leftturn lane. At the current time, there are several different types of applications of dual left-turn lanes in Charlotte. In general, dual left-turn lanes are used in conjunction with a protected traffic signal phase. In some cases, however, there are applications with protected/permissive phases. Also, there is a limited number of intersections where one of the dual left-turn lanes is shared with a through or rightturn movement, as shown in Figure 1. Need for the Study