Electronic motorway signs displaying the price of fuel at upcoming service stations will be in operation from next year.
The Highways England (HE) trial is to be launched on a southbound section of the M5 between Bristol and Exeter in a bid to encourage competition on pump prices.
Drivers will be alerted to the cost of unleaded and diesel from Gordano, Sedgemoor, Bridgwater, Taunton Deane and Exeter services, allowing them to choose the cheapest location to fill up.
If the scheme proves successful it could be rolled out nationally.
HE chief highways engineer Mike Wilson said: "Providing fuel price information is an important part of a bigger picture - we want road users to be more informed and in better control of their journeys.
"This means they'll be better prepared, more inclined to plan breaks and have a positive driving experience.
"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."
Roads minister Andrew Jones said: "The Government is on the side of the honest motorists who have raised concerns for too long about petrol prices at motorway service stations.
"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."
The project will initially run for 18 months from spring next year. HE will monitor the impact on pump prices and whether there are any safety implications such as more drivers running out of fuel.