SEPTA’s seventh annual “trolley tunnel blitz” has begun, and commuters who rely on the system’s century-old trolley lines through Center City will need alternate commuting plans through next Sunday.

The project, which started Friday, requires shutting down the trolley tunnel that runs from 13th Street to 40th Street until 4 a.m. Aug. 19 to allow for extensive maintenance of the five-mile tunnel during around-the-clock shifts.

More than 60,000 riders commute through the tunnel on weekdays. SEPTA chose August for the “blitz” because schools are out and many regular riders take vacations.

SEPTA said the 10-day inconvenience will result in more reliable service for the five trolley lines, part of the nation’s largest trolley system, that pass through the tunnel.

New energy-efficient lighting, track replacement west of 33rd Street, and water-leak repairs are some of the improvements planned. The lines will also receive detailed inspections.

SEPTA advises trolley commuters to use the Market-Frankford Line through Center City until the work is complete.

At 40th and Market Streets, riders can board trolleys at a temporary free interchange for Routes 10, 11, 13, 34, and 36.

An earlier version incorrectly identified the free-interchange location.