The bad news: Pike lane closures are making the Boston commute a lot harder this weekend.

The good news: Crews remain on an aggressive schedule for the repairs, tearing down part of the aging Commonwealth Avenue bridge Saturday to make room for a new section to be installed Sunday.

On Saturday, Massachusetts Turnpike travelers could see crews demolish part of the bridge’s eastbound section, which spans the commuter rail and the Pike’s own eastbound lanes, said Jonathan Gulliver, the state’s acting highway administrator.

However, “things are progressing smoothly, we are hitting our milestones,’’ said Gulliver in a telephone interview Saturday morning.

Things were not ideal throughout the day, however.

In the late afternoon, the Department of Transportation was reporting two- and three-mile traffic backups on the Pike’s eastbound lane, stretching west to Exit 18 in Allston.

“People should avoid using the Mass. Pike if possible over the weekend,’’ Jacquelyn Goddard, a spokeswoman with the state’s Department of Transportation, said Friday.

This weekend and during overnights, commuters on the Pike will find just one lane inbound and two outbound to accommodate the work.

Crews used excavator-mounted jackhammers Saturday morning to break up the bridge road deck, and later in the day, removed the steel beams from that section of the bridge, officials said.

On Sunday, that work will continue, with the eventual goal of installing new spans over the commuter rail and the Pike’s eastbound lanes, he said.

Gulliver said that around midweek, overnight lane closures will change, switching to two inbound lanes and one outbound.

The changes in lane closures are timed with demolition and replacement of the rest of Commonwealth Avenue’s eastbound bridge over the Pike’s westbound lanes, scheduled for Wednesday and Thursday.

“So far there haven’t been any surprises. We put a lot of planning and engineering into where we are right now,’’ said Gulliver.

But even if the project remains on schedule, expect significant workweek traffic woes.

Pike commuters should expect delays of as much as 90 minutes during the weekday morning and evening commutes, said Gulliver, as the Pike is narrowed during the workweek from 5 a.m. to 7 p.m. to accommodate the construction.

He recommended that Pike commuters seek alternate routes into the city.

If you do have to come in, build in all the extra time you can, “even if you have to be in the city a few hours early,’’ said Gulliver.

Work began last Wednesday on the first of a two-stage, $82 million effort to replace the Commonwealth Avenue bridge, which was erected in 1965.

This stage of the project is slated to wrap up Aug. 14. The second stage, scheduled for the summer of 2018, will replace the Commonwealth Avenue bridge’s westbound section.

The weekend work also interrupts commuter rail service for the Framingham/Worcester line, which temporarily ends at Boston Landing station.

The commuter rail service will operate on a normal schedule on weekdays, and another service interruption is planned for next weekend.

On the weekends, rail commuters can transfer to the Green Line’s D branch service at Reservoir, which will be running extra trains to accommodate commuter rail passengers, according to the MBTA’s website.

Additionally, because of the Commonwealth Avenue bridge project, the MBTA commuter rail will not stop at Yawkey Way station on Saturday. Instead, riders will have to be shuttled via buses from Boston Landing, said Goddard.

The MBTA was providing shuttle bus service timed for Red Sox games this weekend and next, the agency said.

Danny McDonald of the Globe staff contributed to this report. John Hilliard can be reached at john.hilliard@globe.com.