Metro pulled about 100 buses off the roads Thursday for unscheduled maintenance work after one caught fire.
The transit system said each one could need hydraulic pump repairs. The part possibly sparked a fire on one bus Thursday on I-495 near Springfield.
Metro pulled its remaining 99 Orion VI model buses off the road as a precaution. The fleet is 10 years old.
Other Metro buses that were in reserve will cover affected routes. Metro said customers should not have major delays today.