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1310.03(2) Left-Turn Lanes and Turn Radii <br />Left-turn lanes provide storage, separate from the through lanes, for left-turning vehicles <br />waiting for a signal to change or for a gap in opposing traffic. (See 1310.03(4) for a discussion on <br />speed change lanes.) <br />Design left-turn channelization to provide sufficient operational flexibility to function under <br />peak loads and adverse conditions. <br />1310.03(2)(a) One-Way Left-Turn Lanes <br />One-way left-turn lanes are separate storage lanes for vehicles turning left from one roadway <br />onto another. One-way left-turn lanes may be an economical way to lessen delays and crash <br />potential involving left-turning vehicles. In addition, they can allow deceleration clear of the <br />through traffic lanes. Provide a minimum storage length of 100 feet for one-way left-turn lanes. <br />When evaluating left-turn lanes, include impacts to all intersection movements and users. <br />At signalized intersections, use a traffic signal analysis to determine whether a left-turn lane is <br />needed and the storage length. If the length determined is less than the 100-foot minimum, <br />make it 100 feet (see Chapter 1330). <br />At unsignalized intersections, use the following as a guide to determine whether or not to <br />provide one-way left-turn lanes: <br />• A traffic analysis indicates congestion reduction with a left-turn lane. On two-lane <br />highways, use Exhibit 1310-7a, based on total traffic volume (DHV) for both <br />directions and percent left- turn traffic, to determine whether further investigation <br />is needed. On four-lane highways, use Exhibit 1310-7b to determine whether a left- <br />turn lane is recommended. <br />• A study indicates crash reduction with a left-turn lane. <br />• Restrictive geometrics require left-turning vehicles to slow greatly below the speed <br />of the through traffic. <br />• There is less than decision sight distance for traffic approaching a vehicle stopped at <br />the intersection to make a left turn. <br />A traffic analysis based on the Highway Capacity Manual (HCM) may also be used to determine <br />whether left-turn lanes are needed to maintain the desired level of service. <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br />Index #5