SHANGHAI, Mar. 8 -- Shanghai plans to create a computer model of its traffic flow to alleviate congestion.

The model will evaluate new traffic policies including the rearrangement of elevated road entrances and electric traffic signs, city planners said yesterday.

The model "will enable us to try whatever ideas and see their possible effects," Cai Yifeng, a city planner with the Shanghai Transportation Planning Institute who is involved in the project, said yesterday.

Software will produce a three-dimensional image of the traffic situation in the city, including in the most congested areas.

Cai and his colleagues receive constant traffic flow data from the city's traffic information center, which collects data through thousands of ground-buried sensors and cameras in downtown.

He said there were congestion hot spots - the entrance to the Inner Ring Road on Guangzhong Road is one example - but it was difficult to find out why they exist and how to relieve them.

With the help of the traffic-flow model, city planners will be able to conduct virtual tests in congested areas - including adding electronic traffic signs, relocating entrances or widening ground roads.

The city government will continue to use satellite positioning equipment to track cab routes, which have been described by transport engineers as the "moving thermometers of traffic congestion" because they use nearly two-thirds of the city's roads.