SAN FRANCISCO (CBS SF) – Early risers who use BART will need to make adjustments starting Monday, as service opens at 5 a.m. due to seismic retrofit work on the Transbay Tube.

The later start will remain in effect through the entire length of the project, which is expected to take three- and-a-half years.

To accommodate the estimated 2,900 riders who use BART during the 4 a.m. hour, transit officials are also launching an Early Bird Express bus service that will serve 21 stations. Additional information and bus schedules can be found here.

Riders who park at stations and use the Early Bird Express will not be able to use kiosks or their Clipper cards to pay for parking. BART said commuters would need either to pay through the BART app or purchase single day passes, and parking rules will remain in effect.

BART officials say the retrofit work may also lead to trains being single-tracked through the Transbay Tube on weeknights.

The transit agency also said trains would also be single-tracked in Downtown San Francisco on some Sundays, to complete electrical power system upgrades. Service changes are expected to change week to week, and riders should check BART’s website for more information.