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Basically, automatic motorway cameras will be tracking whether people are driving in closed lanes, and won't hesitate to lump drivers with a fine if they're breaking the rules.
To be fair, it couldn't be much easier to spot the lanes you can't drive in, as they're marked with a big red X on the overhead signs, so you've got no excuse for not moving over as soon as possible when necessary.
Sharing the news on Twitter, National Highways said that there is 'no eXcuse' and pointed out that it is illegal to drive in a lane that is closed and marked with an X.
Break the rules, and you'll pay the price. In this case, it's a fine of up to £100 and three points on your licence.
They said: "There's no eXcuse - don't ignore the red X.
"It's illegal to drive in a red X lane and motorway cameras can now automatically detect drivers who flout the law.
"You could receive a £100 fine and get three points on your licence. #KeepUsAllMoving."
However, some drivers have criticised the new rules, as SMART motorways aren't the most popular road among those who have to travel them.
This rule is just one of several changes made on 14 September as part of National Highways' attempts to 'make England's motorways and high-speed roads even safer'.
Other changes include updated advice on where to stop in an emergency, and clarification on how variable speed limits can be used to keep traffic moving.
In total, 33 rules of the Highway Code were amended and two new ones were introduced. You can see the updates here.
National Highways chief executive Nick Harris said: "Although our motorways and major A-roads are already among the very safest in the world this new guidance will help road users be even safer.
"It includes clear, practical information such as how variable speed limits work and advice about where to stop in an emergency. This will help drivers use our roads safely and feel safe doing so, and I urge all drivers to read it."
Road safety charity IAM RoadSmart's CEO Tony Greenidge added: "Motorways and high-speed roads are changing and to support the successful implementation of these, IAM RoadSmart welcomes this Highway Code update.
"Clear advice on what to do if you break down on a smart motorway, and the vital importance of strict compliance with Red X signs are particularly important, in addition we would recommend that every driver refresh their knowledge by reading the new document.
"From daily commuters to occasional users, The Highway Code update will help protect drivers and their passengers, as well as keep England's vital road network flowing."
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