As traffic volumes increase on major intersecting arterials, the transportation engineer's challenge is one of optimizing through traffic while providing adequate opportunities for left-turning vehicles. Increasing traffic volumes not only provide a proportionately higher number of left-turning 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.
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