Motorists who commit minor traffic offences such as blocking yellow box junctions and performing illegal U-turns are to be caught on CCTV cameras and sent £100 fines from next month.
More than 80 severely congested junctions will be targeted in a pilot project in London, with local authorities keeping the profits from thousands of penalties issued each day.
The Automobile Association expressed concern that authorities would be overzealous in their enforcement to raise extra revenue.
The scheme is expected to be introduced across the country from next year.
Transport for London refuses to publish the locations of the first 82 enforcement sites, arguing that revealing the sites would result in motorists obeying rules only at those places, instead of believing there is a chance of being caught on camera anywhere.
The offences to be enforced include disobeying no-entry and "no left turn" or "no right turn" signs, driving in pedestrian zones and blocking "keep clear" areas marked in yellow outside schools.
The pilot covers main routes operated by TfL as well as roads controlled by the boroughs of Camden, Ealing, Newham, Croydon, Hammersmith & Fulham and Wandsworth.
Ealing has chosen to pay special attention to schools which have complained that vehicles block school gates, creating a hazard for children. Wandsworth and Newham have identified no-entry signs being routinely abused by drivers and Croydon plans to target drivers who block its tram lines.
But most fines are expected to be generated at junctions covered by yellow boxes which drivers are not supposed to enter unless their exit route is clear. Drivers may enter the box and wait when they want to turn right, and are only stopped from doing so by oncoming traffic, or by other vehicles waiting to turn right.
Nick Lester, director of transport at the Association of London Government, admitted that drivers often became trapped in yellow boxes after following another vehicle.
"There is a certain amount of discretion and you won't be prosecuted if your bumper is over the line. But motorists have to make sensible judgments. If the car in front is zipping through then you could safely follow it. But if it's crawling, then you should wait."
He said poor enforcement of traffic rules was the key problem at a quarter of all London's most congested junctions: "The police, who are currently meant to enforce this, say it isn't a priority for them. By taking over the enforcement we will be able to reduce the delays caused when drivers break the rules to gain one or two minutes' advantage."
Mr Lester said the nine-month pilot would show whether road signs were inadequate or out of date. A high level of fines at a site might indicate the need for better signs. He refused to give estimates for how many fines would be issued but said any profits would be spent on transport improvements. Revenue from traffic offences will be added to the growing pot of money which TfL and councils collect from drivers in bus lanes, the congestion charge and parking fines. Mr Lester said parking enforcement had generated £100 million in profits for London boroughs last year. "If it wasn't for the surpluses the boroughs would find it very difficult to pay for the freedom pass which gives free travel to the over-60s," he said.
Paul Watters, the AA's head of roads policy, said: "We are concerned that CCTV cameras don't give you a chance to explain yourself. The images won't show that you strayed into a junction only because some idiot behind you was blowing his horn." Mr Watters called on authorities to add signs at each junction to make the rules clear. TfL said every junction involved would display a sign saying "Traffic Enforcement Cameras".
The first £100 penalties, which are reduced to £50 for prompt payment, will be incurred on Monday July 5.