Street Design Manual

Section 12.1.5 Traffic Control Devices All traffic control devices should be designed in accordance with the standards and specifications as published in the latest Manual on Uniform Traffic Control Devices (MUTCD) . The typical intersection control shall be two-way stop control, which provides stop control on the side-street intersection approaches and free flow on the main street. All-way stop control may be provided at intersections where traffic volumes or other conditions are consistent with the warrants set forth in the MUTCD. Signal control may only be provided at intersections where vehicle or pedestrian volumes meet the thresholds set forth for new signals in the MUTCD. A roundabout may be constructed at any intersection location where it may be desired in order to enhance intersection capacity, reduce vehicle speeds along a corridor, or enhance intersection aesthetics. Roundabouts shall be designed in accordance with the criteria set forth in Roundabouts, An Informational Guide, Second Edition . Care should be taken in order to ensure roundabouts are not located in close proximity to adjacent stop or signal controlled intersections where long queues may back up into the roundabout. Section 12.1.6 Roadway Transition When constructing a street that will directly connect with an existing street of different width, it is necessary to install a transition taper between the two. The length of taper depends upon the offset differences between the outside traveled edge of the two sections and the design speed of the roadway. When tapers are located on a curve, the separate halves of the roadway should be designed with different curves to create the taper without any angle points in the curvature.

Formulas for determining transition taper lengths are shown below:

Street Width Transition Tapers

For speeds <= 40 mph = ∗ For speeds > 40 mph = ∗

Where, L = transition taper length

W = width of pavement offset (feet) S = roadway design speed (mph)

Raleigh Street Design Manual – Page 87