A London bus is taking to the streets equipped with technology which automatically keeps its speed to local limits.
Intelligent Speed Adaptation (ISA) is being developed by Transport for London (TfL) and uses a newly-introduced digital speed limit map of the city.
TfL also plans to install the ISAs in a taxi and 20 of its own vehicles.
The company claims road casualties in London could be cut by 10% if two-thirds of motorists used the devices.
Speeding points, penalty notices and fines would also be reduced, TfL says.
The technology enables drivers to select an option where acceleration is stopped automatically at the speed limit specific to any road in London within the M25 area.
The device can be disabled at the touch of a button, at which point it reverts to an advisory status where the current, legal speed limit is simply displayed as a driver aid.
We know the technology works, and now we want to know how drivers in all types of vehicles respond to it
Chris Lines, TfL
There is also a complete override switch with disables the system entirely.
The practical uses of the technology will be tested in the six-month trial after which a report will be submitted to the Mayor of London and the technology will be made available to external organisations.
Southwark Council has already expressed an interest in fitting ISA to more than 300 of its vehicles.
The trial will monitor driver behaviour, journey times and the effect that driving within the speed limit has on vehicle emissions.
Chris Lines, Head of TfL's road safety unit, said: "We know the technology works, and now we want to know how drivers in all types of vehicles respond to it.
"ISA is intended as a road safety device, but if Londoners embrace this technology we may well see additional benefits including reduced congestion as a result of collisions, and reduced vehicle emissions, as drivers adopt a smoother driving style."
Tom Edwards, BBC London's Transport Correspondent, has road-tested the device for a day.
He said: "The ISA does work 99% of the time. Now and again it takes a few moments to work out what the speed limit is on the road you're on, but during the day I drove the car around London most the time it shows you the speed limit on a small satnav type screen to the right of the steering wheel.
"There are two modes for the gadget, in the advisory mode when you're within the speed limit it gives you a smiley face but as soon as you go over it turns to a frown and then if you go faster, it becomes a red grimace and starts bleeping.
"In the override mode it won't let you accelerate once you get over the speed limit - so you can have the accelerator pedal on the floor and nothing happens.
"It's unlikely there will ever be the political will to make this kind of device compulsory."
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