Motorists on the southbound stretch of the M5 between Bristol and Exeter will soon be able to compare fuel prices at service stations.
Electronic roadside signs will display fuel prices, enabling drivers to choose the cheapest place to fill up.
Mike Wilson from Highways England, which is behind a trial of the signs, said: "We want road users to be more informed and in better control of their journeys."
The 18-month trial starts next spring.
Mr Wilson said it would help drivers to be "better prepared, more inclined to plan breaks and have a positive driving experience".
He added: "It's still very important for motorists to properly plan their journeys and ensure they have sufficient fuel.
"Running out of fuel on motorways can be hazardous to yourself and other drivers."
Drivers will be alerted to the cost of petrol and diesel from Gordano, Sedgemoor, Bridgwater, Taunton Deane and Exeter services.
If the project is successful it could be rolled out nationally.
Roads minister Andrew Jones said: "This trial will allow drivers to be much better informed about the cost of fuel and make it easier to plan their breaks around the cheapest deals."
Highways England said it would monitor whether there are any safety implications, including drivers running out of fuel.