A plan to ban through traffic from two busy shopping streets through Broadmead is facing a snag – the habits of Bristol's motorists.

The council banned through access to The Horsefair and Penn Street, which divide Broadmead and Cabot Circus, in December. Buses, taxis, emergency vehicles and cyclists are still allowed to pass through, as are disabled drivers and delivery vehicles.

But motorists are so used to driving straight down Union Street and on to The Horsefair that the ban isn't working.

Many drivers are unaware of the restricted entry, and don't see the road signs at the junction of Union Street and The Horsefair telling them about the access. Council officials said that monitoring officers have found the amount of through traffic is not high. But Richard Belt, director of Cabot Circus, said: "The ban isn't working quite as we would have hoped, partly because people are so used to going down that route.

"We always knew taxis and buses would be exempt from the trial, but people's habits are so ingrained that putting signs up hasn't really worked."

The ban is being run as an experiment for 18 months to make the area safer for shoppers and to further pedestrianise the central shopping area, building closer connections between Broadmead and the £500-million Cabot Circus development.

Kate Hartas, a Bristol City Council spokeswoman, said: "So far, monitoring by officers on the streets seems to indicate that the amount of through traffic is not high.

"Most motorists have been parking in off-street parking facilities or accessing premises on Penn Street and The Horsefair – for instance to pick up an item, collect someone, or make a delivery – which they can do legitimately under the order. But officers will need to examine the data following a review."

In a newsletter to shop owners and retailers in Broadmead, Jo Hawkins, Broadmead project manager for Destination Bristol, said the trial to reduce the private vehicles on the route wasn't working.

She told the Evening Post: "The recent addition of the new bold road markings at the junction of Union Street and The Horsefair make the restriction much clearer to motorists and hopefully this will see a significant reduction in traffic passing through the main shopping area."

Anyone wanting to object to an indefinite ban should write to Council House, College Green, PO Box 2156, Bristol BS99 7PH.