Aiming at the problems of traffic jam in road crossing in cities,it analyses the problems existed in flat crossing existing situation,according to the traffic character of the flat crossing of road,from the canalization,the safe crossing of passerby and the traffic control equipment it discusses the design of the improving of flat crossing,to increase the traffic function of crossing.

To these problems such as ecological crisis,traffic jam, and old city reconstruction,etc.

This essay, from the viewpoints of microeconomics, concludes that it can not throughly solve the traffic jam problems simply by means of widening the roads.

For the analysis of cost, controlling traffic flows of highway sections (improves) the conditions of traffic congestions and decreases the social cost.