Vehicle Speed Characteristics and Alignment Design Consistency for Mountainous Roads

摘要

Vehicle drivers continuously make decisions andrnexecute them while driving on a roadway. It requires perception,rncomprehension and prediction of roadway conditions.rnStudies show that the decision-making process andrndriver performance greatly depends on situational awareness.rnDrivers intend to operate vehicles at safe speed basedrnon the roadway geometric features. These features arerncharacterized by gradient, horizontal curvature, length ofrncurves and tangent sections, superelevation, etc. Perceptivernand consistent geometric characteristics of the roadway canrnease the decision making burden and thus minimize driverrnerror. So far, majority of the studies on geometric designrnconsistency are conducted on isolated curve sections inrnplain terrain for traffic with strong lane discipline. Therneffect of gradient is not significant in these terrains. Further,rnthe driving behavior of traffic with weak lane disciplinernis not represented in these studies. Hence, the aim ofrnthis paper is to study geometric consistency of roadways onrnmountainous terrain for traffic with weak lane disciplinerncharacteristics using existing consistency based safetyrnevaluation methods. Isolated horizontal curves with horizontalrncurvature, length of curve and gradient are consideredrnfor the purpose. Sixteen sites in a mountainous terrainrnwith distinct horizontal alignment and vertical profile featuresrnare chosen on a four-lane divided National Highwayrn40 in India. The obtained results indicate that 79 % andrn93 % locations exhibit good level of consistency as perrnLamm’s Criteria I and Criteria II, respectively. It is alsornobserved that average vehicle operating speed at most ofrnthe locations exceeds the design speed.