The city plans to close several blocks of Broadway to vehicle traffic through Times Square and Herald Square, an experiment that would turn swaths of the Great White Way into pedestrian malls and continue Mayor Michael R. Bloomberg’s effort to reduce traffic congestion in Midtown.

Although it seems counterintuitive, officials believe the move will actually improve the overall flow of traffic, because the diagonal path of Broadway tends to disrupt traffic where it intersects with other streets.

The city plans to introduce the changes as early as May and keep them in effect through the end of the year. If the experiment works, they could become permanent. The plan was described by several people who were briefed on it this week.

Mr. Bloomberg was expected to announce the plan Thursday.

A City Hall spokesman declined comment in advance of the announcement.