Central angle intersection points and of the legs of the angle with the circle form a diameter, then is a straight angle. (In radians, .) Let be the minor arc of the circle between points and , and let be the radius of the circle. If the central angle is subtended by , then If the central angle is not subtended by the minor arc , then is a reflex angle and If a tangent at and a tangent at intersect at the exterior point , then denoting the center as , the angles (convex) and are supplementary (sum to 180°). A
Back-in angle parking in traffic delays and considerable risk of collisions with pedestrians, bicyclists, and vehicles. Existing pull-in angle parking spaces can be converted to back-in angle parking by re-striping to flip the angle of the stall markings. Streets with parallel parking have also been converted to back-in angle parking. In either case, the pavement markings are often augmented with signage indicating that vehicles must be backed in. According to the Pedestrian & Bicycle Information Center, back-in angle parking provides motorists with better vision of pedestrians, bicyclists, motor vehicles, and other road users as they exit a parking space and enter moving traffic.