Little Rock`s traffic engineer says the city will close intersections on both sides of the Main Street bridge connecting downtown with North Little Rock on March First. Bill Henry says work on the River Rail streetcar will keep the busy intersections and the whole bridge closed the entire month of March. Motorists wishing to cross the river between the two downtowns will have to use the Broadway or Interstate 30 bridges. Also, Markham and Scott streets will be closed at the Little Rock end of the bridge. The streetcar project is costing nearly 20 million dollars.