Past research has clearly shown that obstructed sight lines at intersections lead to greater possibilities of collisions between left-turning vehicles and opposing oncoming vehicles. Evaluations of the effects of left-turn lane offsets; reported that positive left-turn lane offsets were more effective in reducing intersection left-turn crashes than zero and negative left-turn offsets. Several researchers have developed guidelines for geometric design elements of left-turn offset. The majority of states provide only a limited discussion on this topic. Florida DOT provides the most comprehensive policies and guidance for assuring unobstructed sight lines at left-turn lanes. Recommendations developed in this project center on general policies and guidance for designing offset left-turn lanes for a new edition of MnDOT's Road Design Manual. Recommendations are organized to provide standards; policies; and guidance for new/reconstruction projects and for preservation projects. Topics covered include definition of left-turn lane offset; design factors impacting offset; suggested designs for urban and rural multilane roadways and expressways; accommodating U-turns; pedestrian and bicyclist considerations as well as winter maintenance considerations. Additional recommendations are offered to improve consistency among all MnDOT manuals and guides used for intersection design and operation.
