Left-Turn Lane Maneuver Length

In order to observe the point where vehicles entered a two-way left-turn lane (TWLTL) prior to turning left into a driveway, data were collected in the vicinity of ten unsignalized driveway connections along relatively level roadways with four through lanes. All of these driveways served commercial tracts. The connections were at least 500 ft from the nearest signalized intersection. At four of the sites, the posted speed limit was 35 mph, and at six sites it was 40 mph. For each vehicle, the observer noted whether the lane change was made at a time in which the traffic state in the TWLTL could be categorized as having a standing queue, moving queue, or no queue. The distributions of the distances at which vehicles shifted into the TWLTLs were found separately for the 35 mph and the 40 mph groups, and adjustments were made for the lengths of any queues present. From this, one can infer, for various percentiles of all vehicles entering the left-turn lane, the distance in advance of a connection at which the lane changing maneuver takes place. Knowing the distance in advance of a driveway connection at which unconstrained drivers choose to move from the through lane into the left-turn lane can help those modeling two-way left-turn lanes (TWLTL) in simulation programs, specifying the separation between two successive connections on opposite sides of the roadway, or designing left-turn lanes on roadways with restrictive medians. To these distances, one must also add the length of any standing queues waiting to turn left.