7.4 Design Considerations for Turnouts and Grades

  • Truck escape ramps provide a space for out-of-control trucks to slow down and stop away from through traffic. Table 7.2 lists design guidelines for geometrics and signing.
Table 7.2 Guidelines for Geometrics and Signing of Truck Escape Ramps
Topic Guideline
Geometrics
  • Design ramps so that drivers of runaway trucks can see the entire ramp or most of it.
  • Any service roads adjacent to an escape ramp should be designed to ensure they are not mistaken for the ramp. Providing adequate sight distance eliminates confusion.
  • When a downgrade has two ramps, truck drivers typically prefer the one at a lower elevation.
  • Design ramps so other vehicles on the mainline do not mistakenly enter it.
  • Ramps should be straight and their angle to the roadway as flat as possible.
Signing
  • Locate signs advance warning upstream of ramps to inform drivers of their presence.
  • Install exit signs to clarify the access point.
  • Place signs that read Runaway Vehicles Only and No Parking near ramps to discourage motorists from blocking the ramp.
  • To maximize their impact, advisory signs must explicitly address drivers of at-risk vehicles.
  • Do not post more than five weight classes on weight-specific-speed signs.
  • Minimal signage or signs that do not clearly communicate the magnitude of severe grades can result in dangerous braking on severe grades and overly cautions driving on non-severe grades.

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