right turn lane on lane shift to accomodate left turn lane

[gjeppesen]

I'm not a traffic engineer so bear with me. I want to put in a southbound right turn lane on a 2 lane road. This right turn lane will be along an existing lane shift (approach lane shift) for a northbound left turn lane located to the south of us (both turn lanes for same entrance).

Is this a bad thing to have the right turn lane on the lane shift? Both movements are to the right (lane shift and turn lane) so I wouln't thing it would be a safety hazard.

 

[teeman]

From your description it appears you are proposing to modify a two-lane roadway to provide:

A three lane cross section on the NB approach that includes a NB Thru lane, a NB left turn lane and a SB departure lane;

A four lane cross section on the SB approach that includes a NB departure lane, a shadow lane for the NBLTL, A SB thru lane and a SB right turn lane.

If I have interpreted your description correctly, the concept is ok. The geometric requirements for the shadow lane shift taper and the right turn lane geometry may not exactly match.

The length of the shift taper that forms the right side of the SB shadow lane and aligns SB traffic with the SB departure lane is dependent on approach speed. The elements of the right turn lane (bay taper, deceleration length, and storage capacity) are dependent on approach speed, deceleration requirements, the corner turning radius, traffic volumes and lane traffic control.

I generally reference NCHRP Report 279 Intersection Channelization Design Guide for designing elements of intersections. I think it is still available for purchase, but not available online. Florida DOT has some good online guides in their access permit section for design of site geometry. Your local DOT may have similar publications.