- Exit ramps need to afford vehicles enough space to depart the main freeway lanes and enough distance to decelerate to a speed appropriate for the controlling feature of the ramp. Several design practices support safe driving behaviors:
- Locate and sequence guide signs so motorists have enough time to decide on their route.
- Provide adequate sight distance for motorists to execute appropriate maneuvers.
- Install pavement markings and roadside delineation to indicate the proper vehicle trajectory on the ramp.
- Use a divergence angle of 2 – 5 degrees on taper-type exits to clearly indicate the point of departure from through lanes.
- Provide a taper area on parallel-type exits to indicate the path an exiting vehicle needs to follow. Taper length ratio (longitudinal: transverse) should be between 15:1 and 25:1.
- Deceleration lanes should be long enough for motorists to reduce their speed to the average running speed of the controlling feature at the end of the speed-change lane (see Table 10-5 of the Green Book).
- Mitigate motorist confusion near exit ramps through the following design strategies:
- Proper sequencing and placement of overhead guide signs.
- Clearly delineate the exit ramp
- Clearly delineate the taper, beginning of the deceleration lane, and gore area with pavement markings (e.g., raised pavement markings) as well as roadside delineation.
CONTACT:
Chris VanDyke
Research Scientist | Program Manager
chrisvandyke@uky.edu
