Dynamic Left Shoulder (DLS)

Overview.  RTA is spearheading the inclusion of Dynamic Left Shoulder (DLS) transit priority treatments on freeways in our region. These would complement, and not necessarily replace, the existing Bus On Shoulder System (BOSS) segments along the outside, right shoulder of I-40 and the Wade Avenue freeway in Durham, Wake, and Johnston counties.

The Dynamic Left Shoulder treatment would allow for a public transit vehicle to travel up to 45 MPH on the inside (i.e., left, median) shoulder along authorized segments of area freeways. However, shoulder travel will not be allowed whenever adjacent mainline speeds are higher than 45 MPH.

Current RTA focus.  RTA is focused on advancing the implementation of a DLS pilot for I-40, our region’s most important freeway, via the ongoing Freeway, Arterial, Street, and Tactical (FAST) transit study. A dynamic left shoulder transit priority treatment would directly link with multiple proposed BRT corridors as well as Research Triangle Park and Raleigh-Durham International Airport.

The current express design feasibility study for improvements to I-40 in the Research Triangle Park area (STIP H184316) includes a 14′ wide dynamic left shoulder. In addition, AECOM conducted a prefeasibility study for RTA along the entire length of I-40 between the future Chapel Hill north-south BRT and Raleigh/Wake south BRT corridors in 2021.