Drink driving, distraction and tiredness all cause deaths, but public awareness campaigns can save lives over time – and, ultimately, autonomous vehicles could make them problems of the past. About 10% of accidents are “unavoidable” due to external factors however, according to researcher Ravi Ranjan from Coventry University. “That 10% will not be countered, [even] if we go fully autonomous in 10-15 years.”
These so-called “unavoidable” accidents often relate to road condition. Snow, mud or even leaves can cause a loss of traction. Water lengthens braking distance and lowers visibility. As little as 2-3mm of standing water can cause aquaplaning – a complete loss of grip between tyre and road surface – at 80km/h (50mph). Water has a “huge impact” on accidents, says Ranjan. “When aquaplaning starts, you’re basically sliding with no control at all.”
Water “drastically reduces” friction, says Coventry’s Professor Mike Blundell, who has been working on the problem for decades. “If you are braking hard in an urban environment, that could be the difference between braking in 5m or 10m. A child could be walking out of a school gate – that is a life or death difference.”
So, are fatal road accidents just a fact of life? That suggestion is not good enough for Ranjan and Blundell.
Researchers have done a lot of work on tread patterns, designed to efficiently move water away from tyres. But, says Blundell, “they’re as good as they’re ever going to be. Any improvement is going to be fractional.”
He adds: “The bottom line is, all the things we do with cars now to make them safer, none of these are going to work if there is no friction at these four contact points.”
If tyre improvements are limited, why not stop the wheels from ever hitting standing water in the first place? That is the ambitious aim that led to a potentially transformative bit of new technology – the Run Dry Tyre System (RDTS).
Developed by Blundell, the RDTS is a small device using compressed gas to blast away standing water from the road directly in front of tyres. “Our ambition is that you’re not driving on any kind of wet road, you are driving on a dry road,” says Blundell.
Built using an inexpensive canister of compressed carbon dioxide and a manual switch to activate a solenoid and release the gas, a prototype was recently tested on Horiba Mira’s specialist aquaplaning and wet road test surfaces. Two systems capable of one-second bursts were fitted to the front wheels, and the car did emergency braking and aquaplaning tests with and without the devices activating.
The most significant results were obtained at 80km/h, the researchers said. Aquaplaning was assessed by the test driver trying to steer after the car had lost its grip. Without the RDTS, there was no yaw rate or lateral acceleration from steering. With the system activated, however, the dry patch created in front of the tyres reportedly provided the friction needed for the steering input to generate “measured values of yaw rate and lateral acceleration”.
“Significant improvements” were obtained in braking tests, the researchers said. Driving at 80km/h on wet basalt, there was a 22% reduction in braking distance when the RDTS was activated. Peak deceleration improved almost 60% on the aquaplaning track at 80km/h, going from 0.37g to 0.59g. People in the car said they could physically feel the inertial effects of increased deceleration when the RDTS was fired.
The researchers now plan to use bigger gas canisters for air bursts of three to five seconds. They also hope to run tests with devices installed on all four wheels and aerodynamic blades to shield the stream of air at speeds of 112km/h (70mph) and above.
A crazy idea?
The researchers hope to work with automotive manufacturers and suppliers to get the technology into new cars. On the road, the device would activate if a sensor realises the need for emergency braking in wet conditions.
“This is a disruptive technology,” says Blundell. “Forty years ago, airbags were introduced to cars. When they were introduced, that was a disruptive technology. Nobody had thought of that. There were senior people in the automotive industry who thought it was crazy.”
Introduction of the technology will probably start at the “top end” of the market, says Blundell, but he hopes it will eventually become more affordable and filter down to cheaper cars. Planned improvements for commercialisation include using cars’ compressors to automatically refill canisters after use.
The team is hugely ambitious. Blundell claims the technology could achieve even more than preventing 10% of fatal accidents – something he equates to about 150,000 lives annually worldwide. But for the researchers, just one life would make the whole project worthwhile. “If one mother or father does not get a knock on the door at 4 o’clock because their child is not coming home from school, then I’ve made a just contribution to society,” he says.
Content published by Professional Engineering does not necessarily represent the views of the Institution of Mechanical Engineers.