The annual U.K. MPG Marathon, run over two days (Oct. 18-19) from the Heythrop Park Resort in Oxfordshire, England, to the famed Silverstone Circuit in Northamptonshire, serves two purposes -- to highlight eco-friendly vehicles and to promote efficient driving.

Participants have to plan and drive the most economical route from one place to the other, being scored not just on their vehicle's mileage, but also on how much they eclipse the vehicle's claimed figure.

"The fact that drivers are judged on how much they can improve a car's fuel economy over the official figure is massively important," says event organizer Jerry Ramsdale. "It means you can enter the event in an outlandish sports car or a huge SUV, yet still show the world the benefits of driving economically."

To highlight that, Ramsdale points to the 410-hp V8-powered Mustang convertible driven by former Ford-works rally team pilots Andy Dawson and Andy Marriott.

"By entering a car like the Mustang, Ford is demonstrating how even the most performance-oriented of cars can be fuel efficient if driven in a responsible, eco-friendly manner," explains Ramsdale.

Other vehicles entered in the 2016 event include vans and buses, pickup trucks, motorcycles and scooters, and of course the expected future-minded fuel-cell, electric vehicles and hybrid electric/fuel hybrids.

This year's event features a hydrogen fuel-cell vehicle, a Hyundai iX35 Fuel-Cell crossover utility vehicle, entered by the University of Birmingham.

"We hope that by taking part in the MPG Marathon we can show how sustainable and effective hydrogen fuel is," says Monica Guise, Sustainable Logistics Manager at the University of Birmingham.

And also new for 2016 is a category for vehicles that don't fit the defined categories. One of the entries comes from UK motoring services provider RAC, whose 2015 Patrol of the Year, Charlie Harding, will be driving his fully-outfitted Ford Transit roadside-assistance van.

"With the new Ford Transit Custom, I'm really looking forward to seeing how it performs," says Harding. "I think it will be really interesting to see the MPG results when fully laden with all 500 parts and tools on-board."