Policy described in the AASHTO Green Book (1984 edition) concerning sight distance at ramp terminals is reviewed. Ramp terminal design procedures should be commensurate with design principles for at-grade intersections and required sight distance values should be similar to those for stop-controlled intersection sight distance values. However, sight distance values for ramp terminals are over 21% lower than those obtained from the B-1 curve procedure because of different distance-traversed assumptions. Available sight distance has been recalculated at ramp terminals assuming the Green Book values for stopping sight distance, driver eye height, and object height. Equations were developed to reproduce the B-1 curve and then truck characteristics were substituted for passenger car characteristics to determine the sight distance requirements for a stopped truck. K values needed to produce vertical curves that will provide the required sight distances (i.e., B-1 curve sight distances) both for passenger cars and for trucks are generally greater than Green Book K values used for vertical curve design. Therefore, development of alternative approaches for establishing sight distance values at ramp terminals (and at-grade intersections) should be investigated.
Samenvatting