Avoiding a pedestrian or a bicyclist requires that a driver make accurate judgements of the position and velocity of the object to be avoided. This is a particularly difficult problem for drivers at night, when light levels and consequently visibility are low. We have examined how such aids to visibility as reflectors mounted on bicycles and flashing lights on pedestrians or cyclists influence judgements of speed. We used standard psychophysical methods to determine how, for example, the number and configuration of reflectors on a bicycle wheel affect an observer’s judgement of the apparent linear speed of the bicycle. We have made recommendations concerning the optimum number and placement of reflectors on bicycle wheel spokes. We have also examined the interactions between the translational speed of an object (a pedestrian, for example) and the rate at which a signal light affixed to the object flashes in determining apparent speed. We make recommendations concerning the optimum temporal frequency of flashing for strap-on lights that pedestrians wear at night. In work begun earlier and continued with the support of a grant from the University of California Transportation Centre, we devised a method by which to measure the apparent speed of linear translation of an object moving along a cycloidal path. A cycloid is a combination of translation and rotation and describes the path followed by a reflector on the rim of a wheel. A cycloid is illustrated below. (Author/publisher)
Abstract