To accommodate returning University of Arizona students and anticipated heavy traffic, the North Fourth Avenue underpass at East Ninth Street will be closed to motorists.

The closure, which will affect southbound vehicles only, was to begin Thursday night and will continue through Saturday between 7 p.m. and 2 a.m.

During the closure, the Sun Link Streetcar and bicyclists will be allowed to use the southbound lane through the underpass. Pedestrians will have access to the southbound sidewalk as well.

The city of Tucson Transportation Department plans to monitor travel patterns this weekend and if the closures prove to be successful in easing congestion, the practice may be carried on into the foreseeable future, spokesman Michael Graham said.

The city also has taken measures at the Congress Street, Fourth Avenue and Toole Avenue intersection where increased activity has caused gridlock. Permanent adjustments have been made to traffic signals, improving traffic flow.

Motorists are urged to use caution when traveling along North Fourth Avenue and in the downtown area.

Contact reporter Alexis Huicochea at ahuicochea@tucson.com or 573-4175. On Twitter @AlexisHuicochea