The Crosstown Expressway will remain open after its next step of construction begins Thursday, but its traffic lanes will drop from six to four.

On Monday, Charleston Mayor Joe Riley, his staff and consultants offered advice to motorists who want to avoid delays on the peninsula's main east-west thoroughfare, one used by more than 50,000 cars and trucks each day.

The biggest inconvenience might be for those traveling west on the Crosstown who use Sheppard Street to reach Rutledge Avenue heading south.

Sheppard will be closed off completely between Rutledge and the Crosstown, so they will have to find a different route, possibly exiting a few blocks earlier onto King Street.

Those entering downtown via Interstate 26 might want to exit onto Rutledge Avenue, Morrison Drive or King or Meeting streets instead of following the interstate onto the Crosstown.

Motorists entering the peninsula from U.S. Highway 17 might want to use Lockwood, Calhoun, Cannon or Bee streets instead of the Crosstown.

Those using the Crosstown to travel across the county might want to use Sam Rittenberg Boulevard, the Northbridge and I-26 to the Ravenel Bridge instead -- a route that's two miles longer but might save time, particularly during peak traffic hours of 7-9 a.m. and 4-6 p.m.

The city's police and transportation department will monitor the traffic flow, as will the S.C. Department of Transportation. The timing of traffic lights could get tweaked as a result.

"We expect the first few days of travel will be the most difficult," Riley said, urging motorists to be patient.

The two lanes must be closed because construction crews will be digging trenches up to 12 feet deep to install new drainage lines and boxes and the foundation for a wider, raised median. The Crosstown's median is going from 2-4 feet to 7 feet in width.

The expressway is expected to return to a six-lane highway once construction is done around late May.

Riley said contractor O.L. Thompson Construction Co. Inc. is expected to have a crew working around the clock. The company has a mix of incentives and penalties to encourage completion as early as possible, he said.

The Rev. Randolph Miller, whose Nichols AME Church on Kennedy Street has been affected by the ongoing work, appeared at Riley's press conference to support the mayor.

Miller -- whose parishioners have had cars flooded because of the area's drainage problems -- called the work "a temporary inconvenience for a permanent improvement."

Reach Robert Behre at 937-5771.