Three Range Rover diesel hybrid prototypes have completed the ultimate engineering sign-off test by traversing 13 countries over 53 days from Solihull, UK, to Mumbai, India.
It was the world's first hybrid expedition along the Silk Road and one of the boldest driving adventures pursued by Land Rover.
Hostile conditions on the route included asphalt roads riddled with vast potholes, dusty desert trails in 43C heat and many kilometres of mud and gravel tracks and cattle trails.
River crossings, passes clinging to the edges of mountains partly blocked by rock falls, the thin air of extremely high altitudes and the dense and erratic traffic of Chinese and Indian roads all added to the test of man and machine.
The Silk Road 2013 expedition was the final validation test for the Range Rover Hybrid before it is signed off for production. From the home of the Legend in Solihull, it blazed a trail through France, Belgium, Germany, Poland, Ukraine, Russia, Kazakhstan, Uzbekistan, Kyrgyzstan, China (including Tibet), Nepal and India.
For much of this distance, the expedition followed the legendary Silk Road trading routes that first connected Asia with Europe more than 2500 years ago. Overnight halts were made in hotels, hostels and tents at many of the same staging posts visited all those years ago by Silk Road merchants, missionaries and mercenaries.
Where the north and south Silk roads split, near the remote city of Kashgar in north-western China, the expedition pioneered a mountainous route never previously completed by a vehicle from outside the country and never previously seen in its entirety by any Westerner, the Xinjiang-Tibet highway, which put the new Range Rover Hybrid through its paces at heights of over 5300 metres above sea level.
Seven consecutive days were spent at altitudes between 3350m and 5379m. At such heights, oxygen content in the air is reduced from the 21 per cent found at sea level to as little as 10 per cent, making movement more difficult for humans and internal combustion engines.
The Range Rovers continued to make good progress, despite being laden with heavy loads, including luggage, camping gear, food, medical equipment and aerodynamically unfriendly roof-racks carrying spare wheels, tyres and jerry cans of fuel.
Negotiating tracks so sticky with mud they were impassable to other types of vehicle, the Range Rover Hybrid's engine combination proved its worth - with a 35kW electric motor supporting the TDV6 3.0 litre turbo-diesel engine.
Land Rover development engineers closely monitored data loggers fitted to each car, sending back more than 300 gigabytes of detailed technical records to their engineering team in the UK.
The purpose of the expedition was not to test the reliability of mechanical components, which are already proven, but to fine-tune the calibration of engine and transmission software to ensure perfectly seamless performance in all terrains and extreme temperatures and altitudes.
Technical setbacks reflected the roughness of the road surfaces: there were 15 punctures among the expedition's three Range Rover Hybrids and four support vehicles, four wheels damaged by deep potholes, and four windscreens cracked by stones thrown up on loose surfaces.