determining need for left and right turn lanes

[cimmeron]

We are revising our land developemt ordinance and are interested in studying different methods for determining when a left turn or right turn lane into a residential development is warrented.Can anyone offer suggestions

 

[ACtrafficengr]

There are two that I can think of:

Volume. See the intersection design chapter of AASHTO PoGDoHS (Green Book). It's based on percentage of left turn traffic, and opposing volume.

Crash history. If people waiting for a gap in traffic to make a left turn are getting rear-ended, a left turn lane will help. You can expect up to 48% crash reductions at 2-way stop controlled intersections. Crash reductions at signals are lower. There is a summary of this study on the Turner-Fairbanks highway lab website.

Or you could require a roundabout. <grin>

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[teeman]

The Transportation Research Board has recently published an Access Management Manual that provides some guidance on Auxiliary lanes (right and left turn bays). There is also an old Federal Highway Publication, Technical Guidelines for the Control of Direct Access to Arterial Highways (FHWA-RD-76-87) that provides guidance on this issue. The TRB report is readily available form the TRB Bookstore. The FHWA report might be available from your local FHWA divisional office.