6.2 Intersection of two-way streets Consider the intersection of two major avenues near the center of a city. The intersection is controlled by a set of traffic lights. Both avenues carry two-way traffic.

Cars wishing to make a right turn at the intersection incur a "penalty" of two time units; those making a left turn, a penalty of four time units; and those continuing on a straight course, a penalty of one time unit. No U-turns are permitted.

Draw a network model of this intersection. The model should be a finest-grained one, so that all possible actions of motorists at this intersection can be accounted for.