Road design

Table of Contents

9.3.2 Ramp Gradients on Service Interchanges

The vertical alignment of an entry ramp (i.e. sag and crest curves) should be designed for the operating speed at the point being considered. In the case of a crest vertical curve at an entry ramp, the acceleration distances in Table 11.2 can be used as a guide to determine an appropriate operating speed for the crest.

For exit ramps, the vertical alignment should be based on the likely operating speed. This can be estimated using the deceleration rates in Table 11.1 based on the mean free speed of the through road (about numerically equal to the speed limit) at the nose decelerating down to the posted speed on the diagonal exit ramp. It is preferable that entry ramps are located on a downgrade and exit ramps on an upgrade.

Diamond-type ramps

The maximum gradients for diamond ramps are shown in Table 9.2.

Table 9.2: Maximum ramp grades for diamond ramps

Ramp typeGrade orientationDesirableMaximum
Exit rampDownhill–4%–6%
Uphill+6%+8%
Entry rampDownhill–6%–8%
Uphill+3%+5%

Loop ramps

The maximum gradients for loop ramps are shown in Table 9.3.

Table 9.3: Maximum ramp grades for loop ramps

Ramp typeGrade orientationDesirableMaximum
Exit rampDownhill–3%–4%
Uphill+5%+7%
Entry rampDownhill–6%–8%
Uphill+3%+5%