A ramp from an expressway with a design speed of 30 mi/h connects with a local road, forming a T intersection. An additional lane is provided on the local road to allow vehicles from the ramp to turn right onto the local road without stopping. The turning roadway has stabilized shoulders on both sides and will provide for a onelane, one-way operation with no provision for passing a stalled vehicle. Determine the width of the turning roadway if the design vehicle is a single-unit truck. Use 0.08 for superelevation.
What will be an ideal response?
The first step is to determine the minimum radius of curvature for the
ramp, using Equation 3.34. Coefficient of side friction can be seen in Table 3.3:
R = u2 / 15(e + fs)
R = (30)2/15(0.08 + 0.20)
R = 214.29 ft
From Table 7.5, determine appropriate pavement width, W, knowing that:
a. Operational requirements: Case I – one-lane, one-way operation, no
provision for passing a stalled vehicle
b. Traffic conditions: Type B – SU is the design vehicle
c. Edge of pavement treatment: Stabilized shoulder
Using the table, interpolating for R = 214 ft, W = 15 ft
Therefore, the width of the turning roadway should be 15 ft.
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