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FHWA Home / Safety / Intersection / Strategy B15. Convert Offset T-Intersections to Four-Legged Intersections

Strategy B15. Convert Offset T-Intersections to Four-Legged Intersections

NCHRP Report 500 / Volume 5: A Guide for Addressing Unsignalized Intersection Collisions

WHERE TO USE

Unsignalized offset T-intersections where through volumes on the cross street are very high.

Diagram showing the realignment of two T-intersections to create a four-legged intersection.
By realigning a roadway, T-intersections with inadequate storage space between them can be combined into a single 4-leg intersection.

DETAILS

For some unsignalized offset T-intersections with very high through volumes on the cross street, the best method of improving safety may be to convert the intersection to a single four-legged intersection. This conversion to a four-legged intersection can be accomplished by realigning the two cross-street approaches to meet at a single point along the major road, thus creating one four-legged intersection.

KEY TO SUCCESS

Depends upon the through volume of the cross street. If through volumes are low, the intersection may be safer if left as two offset T-intersections. Two offset T-intersections with low cross-street through volumes are generally safer than a four-legged intersection.

ISSUES

There should be no potential difficulties with this strategy, as long as the resulting four-legged intersection is properly designed and traffic control devices are properly used.

TIME FRAME: Medium

This strategy requires an implementation time of 1 to 4 years. At least 1 year is necessary to work out the details of intersection approach relocation and to communicate the plan to affected businesses and residents. Where relocation requires right-of-way acquisition and/or demolition of existing structures, an extensive project development process up to 4 years long may be required.

COSTS: High

Converting two offset T-intersections to a conventional four-legged intersection involves the realignment of at least one intersection approach. The cost of this type of construction project is usually high. Furthermore, additional right-of-way will generally need to be acquired.

EFFECTIVENESS

TRIED: It is expected that this strategy would reduce crashes involving left-turning traffic from the major road onto the cross street at each of the two T-intersections. It can reduce or eliminate safety problems associated with insufficient spacing between existing offset T-intersections.

COMPATIBILITY

The conversion of two offset T-intersections to a conventional four-legged intersection may be used in conjunction with most other strategies for improving safety. In many cases, the purpose of relocating an intersection approach may be to make those other strategies feasible.

For more details on this and other countermeasures: http://safety.transportation.org



For more information contact:

FHWA Office of Safety Design
E71, 1200 New Jersey Avenue SE
Washington, D.C. 20590
(202) 366-9064
http://safety.fhwa.dot.gov

FHWA Resource Center – Safety and Design Team
19900 Governor's Drive, Suite 301
Olympia Fields, IL 60461
(708) 283-3545
https://www.fhwa.dot.gov/resourcecenter

Logo for FHWA and logo for the FHWA Office of Safety, which reads 'Safe Roads for a Safer Future – Investment in roadway safety saves lives.'

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Page last modified on September 4, 2014.
Safe Roads for a Safer Future - Investment in roadway safety saves lives
Federal Highway Administration | 1200 New Jersey Avenue, SE | Washington, DC 20590 | 202-366-4000