Only eight LRT trains were available for much of the Friday afternoon rush hour service after the Confederation Line experienced more problems during the morning, including a loss of train communications and flat wheels.

OC Transpo said it was deploying 20 R1 replacement buses and an additional 10 buses from high-frequency routes to supplement afternoon rush hour service.

The plan for supplemental buses is based on lower-than-usual ridership, since many students have no school Friday as it's a professional activity (PA) day. It's also the eve of the Family Day long weekend.

Four transponders were damaged when trains ran over unidentified "debris" on the westbound track between Tunney's Pasture and Bayview stations, according to a memo from OC Transpo boss John Manconi sent around midday Friday. Manconi did not elaborate on the nature of the debris.

Transponders communicate the location of trains to the central control system. When they aren't working properly, the system automatically stops the trains from moving. The light rail system then has to be run manually, with operators forced to wait for authorization from the control centre before proceeding.

Naturally, trains must travel at much slower speeds in areas where they can't automatically communicate with the central control centre.

A second memo sent later in the afternoon said the transponders had been repaired.

The quick braking caused by the transponders going down also caused "wheel flats" on four trains, which then had to be taken out of service, according to the memo.

Manconi had originally stated that Rideau Transit Group would be providing 10 trains for the afternoon peak hours, which it did for a time. But two additional trains had to be pulled from service for flat wheels.

The city paid for a fleet of 17 double-car trains as part of the $2.1-billion Confederation Line project.