A high-tech system that changes speed limits in response to road conditions is to be introduced on a stretch of the M4 in south Wales hit by congestion.
The variable speed limits should be in place between junction 24, Coldra, and 28, Tredegar Park, for Newport's Ryder Cup golf tournament next October.
Traffic sensors calculate speed limits, which are displayed on overhead signs.
But business leaders are concerned that overnight road closures to install the system will "cause chaos".
Experts say the £7m variable speed limit scheme will improve congestion and the environment by keeping traffic moving at a constant pace.
It will be the first time the system has been used in Wales, although it has been used for a number for years in England, including on the M25 and M42.
The new system will replace the average speed cameras which have been installed along the stretch of the motorway to keep traffic moving at up to 50mph while work is carried out to improve the route and install variable speed limit sensors.
At the same time, the assembly government said sections of the motorway will be closed overnight from 2000 to 0530 "intermittently" over the next 11 months.
Business leaders in south Wales cautiously welcomed the new speed limit plans, but said their immediate concerns were about the overnight road closures.
David Russ, managing director of South Wales Chamber of Commerce, which represents around 700 businesses, said they feared it would disrupt deliveries.
"It's a lot of pain before the gain, particularly during the recession," he said.
"The message that Wales is open for business is not going to go down very well if the main artery in to and out of Wales is closed.
"Businesses try to get a lot of their traffic out and around the country throughout the evening when the roads are quieter."
However, the RAC Foundation said that when the new speed system is installed, it will mean a more efficient and less frustrating journey along the M4 for motorists.
"Anything that will keep the traffic flowing smoothly and put an end to stop-start motoring has to be a good thing, not least for the environment," said a spokesman.
'Road to nowhere'
"Cars produce the least amount of CO2 when they are travelling at a steady speed rather than accelerating and decelerating, or sat stationary in a jam.
"A constant flow is also good for safety. It reduces the risk of drivers piling into the back of stationary traffic and cuts down road rage caused by drivers thinking they are on the road to nowhere."
He added that travelling at a "steady 40 or 50mph" means that journeys tend to be quicker than travelling fast and then hitting traffic jams.
A Welsh Assembly Government spokesman said: "By controlling the speed of traffic at times of heavy flow this system will reduce congestion and accidents associated with heavy braking and improve air quality."
The assembly government scrapped plans for an £1bn M4 relief road around Newport in July, saying its estimated costs had soared.
It said it was working on "alternative schemes" for the motorway.