Average speed cameras: Your views
A dual carriageway in east London has become the latest road to have a set of average speed cameras fitted permanently.
84 cameras have now been switched on along the A13, between Canning Town and the Goresbrook Interchange.
Transport for London say there were over 400 accidents there between 2007 and 2009.
The system is normally only used in amongst roadworks to protect workmen.
It works by positioning cameras above the road at every junction and recording your registration, plus the time, as you pass under them.
When you exit the A13 or drive through the speed limit area those details are taken again.
That allows your average speed to be calculated.
It's hoped the system - which has replaced fixed and mobile safety cameras - will reduce crashes by around 30%.
Newsbeat's been to use the A13 and speak to some of its regular users.
Jamie Suter, 20
"I think they're a good idea.
"Making sure everyone's sticking to the speed limit is a good thing.
"My mates will have to stick to the speed limit otherwise they'll get done.
"Keeps everybody safe."
James Patten, 26
"Nightmare. The 50mph speed limit will make everything too slow for such a busy road.
"It's going to cause more accidents if anything because drivers won't be concentrating fully.
"I live in Southend and go up and down here every day and I've never thought the speed limit was an issue."
Craig Harper, 19
"I've always known this road to be 70mph so now they have this new speed limit in place that's what's going to cause accidents.
"People not paying attention will go into the back of someone when they slam their brakes on.
"I had to pay more attention to my speedo than the road this morning.
"There were people around me speeding which I had to concentrate on."
Vince Barry, 20
"Driving already costs too much.
"Now there's more chance of getting caught speeding along here.
"I do think it's a good idea though.
"Makes everyone keep a normal speed and hopefully keeps them in one lane."