Mechanical bollards used to enforce the Oxford Transport Strategy have been repeatedly malfunctioning, according to a leading county councillor.

David Robertson, executive member for transport, said the rising bollards used in Broad Street and Turl Street were "notoriously unreliable" and the authority was waiting for a suitable time to replace them with more modern equipment. He added some cars might have caused problems by accidentally colliding with the bollards.

The bollards in Broad Street broke down earlier this week, which meant traffic could illegally use the junction with Cornmarket Street.

Mr Robertson said: "Unfortunately, the bollards are repeatedly malfunctioning and this makes a mockery of the Oxford Transport Strategy. We will certainly consider alternatives in the future because our confidence in the technology has been shattered."

Traders in Broad Street were pleased with the county council's decision to restore about 20 parking spaces last year, after 50 were scrapped.

Drivers can park for half an hour for free but the council decided last December to change this to one hour pay-and-display.

Mr Robertson added: "We are waiting for Buckinghamshire County Council to process the traffic order before we can make the switch."

John Moyle, who runs Boswell's department store, said: "I am in favour of having the bollards there because I think it is safer for traffic not to be able to turn left into Broad Street.

"I am more concerned about the work being carried out in Cornmarket Street."

Work to repave Cornmarket is due to finish at the end of the summer, although it is running three weeks' behind schedule.