Tri-Rail passengers should expect delays on the weekends for the rest of the year so several crossings can be repaired.
The delays could last 30 minutes or longer.
The work must be done before early March, when Tri-Rail plans to roll out a new hourly schedule on weekends and holidays. Currently, trains run every two hours on those days.
The weekend expansion of service is Tri-Rail's first since 2007, and officials credit a boost in demand, especially among those who ride to the region's three major airports. Tri-Rail trains don't stop directly at each airport, but instead drop riders at nearby stations where they can board shuttles to and from the airports.
For years the agency has received requests to run trains more often on the weekends.
Tri-Rail spokeswoman Bonnie Arnold said the new service will give people who work on the weekends the option to take the train instead of driving. "Many end up driving on the weekend because of the schedule," she said.
About 5,000 passengers a day currently ride Tri-Rail on the weekends, Arnold said.
Plans for the new service were announced in the spring. Tri-Rail still is in the process of hiring and training additional crew members to operate the trains.
Tri-Rail runs along a 72-mile corridor mostly west of Interstate 95, from Mangonia Park, just north of West Palm Beach, to Hialeah. Currently, the southernmost station at Miami International Airport is closed and being rebuilt as part of a giant transportation hub east of the airport.
Officials were unable to provide a list of the crossings which will be undergoing repairs.
Tri-Rail's last expansion — running 50 trains on weekdays and 16 on weekends and holidays — was a result of a second track being added and a taller bridge being built over the South Fork of the New River in Fort Lauderdale.