The paper reviews the stopping sight distance (SSD) design parameters and examines the need for trucks’ design SSD values in addition to the design values for cars. During the years the braking systems of vehicles have improved significantly, the deceleration ability increased, and thus, the braking distances became shorter. The paper recommends on SSD deceleration coefficients, and SSD design values based on recent research of braking characteristics from Germany and United States. The importance of trucks’ design SSD values has been examined for crest and sag vertical curves. The driver eye level of 2.4 meters did compensate on the inferior braking of trucks in the design process of crest vertical curves. However lower trucks with driver eye level of 1.8 meters resulted in larger vertical curve radii than passenger cars, particularly in multilane highways when the design speed is larger than 80 km/h. Moreover, the need for trucks design SSD values has been found essential in designing sag vertical curves. Recommended truck SSD design values have been supplemented.
Keywords: friction; deceleration coefficient; stopping sight distance; design speed