RESTRICTIVE MEDIANS AND TWO-WAY LEFT TURN LANES: SOME OBSERVATIONS

This conference presentation addresses the choice of median alternatives from the perspective of the left turn problem. The treatment of left turns is a major access management concern. Left turns at driveways and intersections may be accommodated, prohibited, diverted or separated, depending upon specific circumstances. The basic choices for designing the roadway median along many highways is whether to install a continuous two-way left turn lane or a non-traversable median on an undivided roadway, or to replace a two-way left turn lane with a non-traversable median. These treatments improve traffic safety and operations by removing left turns from through travel lanes. Two-way left turn lanes provide more ubiquitous access and maximize operational flexibility. Medians physically separate opposing traffic, limit access, clearly define conflicts and provide better pedestrian refuge; but adequate provision for left and U turns is essential to avoid concentrating movements at signalized intersections. This discussion shares some of the safety benefits of these treatments as reported in National Cooperative Highway Research Program (NCHRP) Project 3-52 for studies conducted since 1970.