Positive Offset Turn Lanes

Image Source: FHWA

DEFINITION AND DESCRIPTION

The typical geometry and operation of signalized intersections can present several challenges. Sight distance is important for drivers to identify acceptable gaps in opposing traffic. Opposing left-turn lanes are typically aligned directly across from one another and immediately adjacent to the through lanes. Thus, a left-turning vehicle in the left-turn lane can obstruct the view of oncoming vehicles, particularly those in the opposite left-turn lane.  For right-turn lanes, this typically involves right-turning vehicles from the major road and vehicles entering the intersection from the minor road. To improve sight distance and safety at intersections, the use of offset turn lanes is recommended.

Implementation Categories

CONSIDERATIONS

• Applicable at any intersection with sufficient right-of-way.
• Recommended at intersections with permissive left turns or at unsignalized intersections with high left turn volumes and high speeds.
• If a positive offset cannot be achieved, no offset is preferrable to a negative offset.
• Drainage on projects with depressed medians will need to be addressed.
• Recommendations for offset left turn lanes are included in HD-902. Typical markings are addressed in Standard Drawing TPM-206. 
• Needed offset distances for sight triangles vary based on intersection geometry.
• Positive offset left-turn lanes reduce fatal and injury collisions 36% (Persaud et al., 2009).

APPLICATION

• Provide positive offset turn lanes at intersections with opposing left turns. At intersections with adequate pavement width, left turn offsets should be considered during pavement resurfacing.

example

Image Source: Google Earth, Lexington, KY