Learner drivers in England, Wales and Scotland are now allowed to have lessons on the motorway.
Previously only those who had passed their test could do so, but lessons are now allowed in a dual-control car with an approved driving instructor.
The government says the move will help learners gain experience to drive safely.
The law change has been welcomed by the AA and RAC Foundation, among other motoring groups.
Road safety minister Jesse Norman said: "Britain's roads are among the safest in the world, but road collisions remain the second biggest killer of young people.
"Allowing learner drivers to have motorway lessons with a qualified road safety expert will help more young drivers to gain the skills and experience they need to drive safely on motorways."
Top tips for learners
Instructor Sharon Starr, whose driving school is based in Stoke Newington, north London, is in favour of the plans - but says that many instructors do not offer motorway lessons because they perceive them to be more dangerous. She has this advice for first-time motorway drivers:
- Keep calm. The most important thing is to keep calm, and remember your instructor is there to help if you have a problem. Motorways are similar to dual carriageways - which learners have already driven on - so it's the same but a bit faster.
- Plan ahead. Sometimes you need to ease off the accelerator to create the gap ahead. You need to build up speed quite quickly when you are joining the motorway.
- Don't hesitate. If you hesitate while joining the motorway or changing lanes you can put yourself or other drivers in danger. Once you've begun to move, they are expecting you to go.
- Watch speed limits. Lots of people don't realise the speed limit isn't always 70mph. There are many stretches where it is 50mph and this is enforced by average speed cameras so you need to be careful.
As many as 8% of licence holders avoided motorways for at least six months after passing their test, an AA poll of more than 20,000 motorists suggests.
More than a quarter said they felt scared when they did drive on a motorway for the first time.
Edmund King, director of the AA Charitable Trust, said: "Young drivers are drastically over-represented in crashes.
"This change, which will help broaden the opportunities they have while learning, is very positive.
"It is somewhat perverse that five minutes after passing the driving test a new driver could venture alone on to a motorway without having had any motorway tuition."
Rural, urban or motorway - where is it most dangerous to drive?
The number of collisions is higher in urban areas however there is a greater chance of dying on rural roads.
In the period 2011-15 the average number of fatalities occurring on rural roads per year was 987 compared with 585 on urban roads.
Over the same time period an average of 90 people per year were killed on motorways.
Serious and slight injuries were higher on urban roads than rural.
In 2015 slight injuries received on rural roads totalled 34,536 compared with 79,028 on urban roads in the same year.
Carly Brookfield, chief executive of the Driving Instructors Association, says rural roads can carry more risk.
"There is a lack of proper lighting, people take more risks when there are less people around and some drivers treat quiet roads like a challenging race track," she says.
Phil Hurst, who trains driving instructors, says: "Most driving instructors are aware of the statistics and will try to get learners on to rural roads, where possible.
Source: Royal Society for the Prevention of Accidents and Department for Transport
A fifth of all fatalities on Britain's roads in 2016 involved crashes where a driver was aged 17-24, despite those drivers making up just 7% of all licence holders, Department for Transport figures show.
There were 1,810 deaths on UK roads in the year to September 2016.
Road safety charity Brake urged the government to introduce a graduated driver licensing system including restrictions for a certain period after passing the test, such as a late-night driving curfew.
Director of campaigns Joshua Harris said: "While today's move is a small step in the right direction, a total overhaul in the way in which we learn to drive is urgently needed."