Car hire company Avis has created a scientific formula to determine what the most adrenaline-fuelled roads in the world are.

Lead researcher in developing the Avis Driving Ratio was quantum physicist Dr Mark Hadley. He said: “There are four key phases of a drive – bends, acceleration, cruising and braking.

“A great driving road strikes just the right balance between the phases so you get the exhilaration of speed and acceleration, whilst corners test your driving capabilities and long stretches allow you to enjoy the scenery.”

According to Hadley, the optimum ratio is 10:1 – ten seconds on a straight compared to one second spent on a bend.

Here are five routes that combine stunning scenery with challenging hairpin bends and death-defying sheer drops for the ultimate road trip.