A frustrating construction project to carry Metro's Green Line over freight railroad tracks along Harrisburg begins its most traffic-troubling detour on Sunday.

To expedite construction of the rail overpass near Hughes, the contractor will close Harrisburg from Caylor to 66th, a three-block area lined with local businesses. The closing will last 90 days, according to Metropolitan Transit Authority.

Detours cover a much larger area than the closing area. Eastbound traffic is being directed right on Lockwood and then left on Polk. Drivers can then turn left on 69th and return to Harrisburg. The westbound detour is a right on Caesar Chavez, a left on Canal and then a left on Lockwood.

During the detour and street closing, Metro is encouraging people to visit shops in the area, affected by years of light rail construction.

The lengthy work schedule and various related frustrations have eroded goodwill between Metro and some East End business owners. The relationship has worsened as Metro said unforeseen underground conditions delayed construction.

Completion of the overpass is now expected to take until mid-September, four months later than Metro officials told residents in October.

To help struggling businesses, Metro extended a business assistance program for shops and restaurants that could demonstrate losses during the construction. The agency is among very few that award money for lost sales.

Some business owners, however, have said the assistance requirements are too stringent and do not do enough to compensate them for months, if not years, of lost revenue.