This report is concerned with problems of vehicle eye-height, with particular reference to trucks. The analysis indicates that the inferior braking of truck on vertical curves is compensated for, on the average, by increased visibility due to raised eye-height. However, this is not true for the long stopping distances required in the case of heavily loaded trucks. In particular, the cab-under truck design, with eye-height barely above .91 meters does not have the visibility advantage of conventional trucks and consequently does not have any compensation for inferior braking ability. Passing zone markings, standardized for passenger cars, are not adequate for trucks. Trucks require 50 percent more distance than passenger cars to pass on two-lane roads. The higher eye-height advantage does not fully compensate on crest vertical curves, for the passing disadvantage. It is suggested that an explicit procedure be designated for determining the geometric design eye-height standard. The methodological considerations underlying such a procedure are discussed. It is shown that the adoption of the 1.07 meters (3.5 foot) eye height standard, presently under consideration, would result in a 2 1/2 percent reduction in design sight distance on vertical curves barely long enough to meet geometric construction standards. (FHWA).
Abstract