Motorists have been pictured still using Bristol Bridge in the city centre - despite route being closed to general traffic.
The closure was introduced by Bristol City Council to tackle air pollution in Bristol.
However, car users are still using the bridge - although full signage is not in place.
The council has said those caught will be fined £60, but to begin with warning letters will be sent out.
Cameras will be introduced at the end of Baldwin Street and in Union Street soon to catch those flouting the rules.
A Bristol City Council spokesperson said: “We are monitoring the success of the new restrictions on Bristol Bridge and the council will issue penalty charge notices if motorists are not adhering to them.
"Fixed penalty notices will charge unauthorised vehicles the usual fee for entering a bus gate, which is £60 with the option of a 50 per cent discount if it is paid within 14 days.
"We will also be increasing signage in the area to inform through traffic of the closure, and unauthorised vehicles using the route can expect fines in the near future.
"These measures to divert traffic away from the city centre will help to improve air quality as well as making it easier to walk, cycle and catch the bus in the city centre.”
The closure has been brought in alongside the pedestrianisation of the Old City and are part of a package of major changes being accelerated to transform Bristol’s transport network.
Councillor Kye Dudd, cabinet member for transport, said: “All of these major changes to key Bristol roads will make a massive difference to the quality of our air as we divert traffic away from the city centre.
“These transformative measures will create a more connected future for everyone, with cleaner air, safer and better public transport, and improved walking and cycling routes. They will also support social distancing during the Covid-19 pandemic.
“These important changes will inevitably result in a period of adjustment as we all adapt, but they are crucial for protecting public health, encouraging more efficient travel, and making bus services more reliable in the long-term."
The council has said the measures are being done on a temporary basis initially and it will assess how they are working before permanent changes are made.
