Imagine joining the motorway in the near future and seeing a 50mph speed limit sign, but no roadworks, no accident and no obvious reason to slow down. This time, the aim is to save fuel.

UK diesel prices have hit an all-time high, with the average litre costing almost £2. Petrol prices are also rising, mainly due to disruptions to global oil supplies.

The UK’s National Emergency Plan for Fuel, last updated in 2024, includes measures to reduce demand in the event of a severe disruption, including lower road speeds. The International Energy Agency has also recommended speed reductions as a way to cut oil demand during a supply crisis.

One proposal, recently resurfaced by British tabloids, would see a 50mph limit on motorways. This would mirror the 50mph limit imposed during the oil crisis of 1973, when the UK government took a range of special fuel-saving measures.

But in 2026, how much fuel would such a limit actually save?

The basic physics is straightforward. Cars use more fuel at higher speeds........

© The Conversation