I average 18mph (burst of up to 30mph) on a7 mile ride and I have never been unable to hear approaching cars from behind. Do I trust my ears alone? No. But I've never been surprised by Prius, Volt, Tesla Roadster, or any other hybrid or electric vehicles. In biking events or on bike paths I can even hear approaching bicycles from behind (bike chain, wind, and tire noise). So I'm surprised that wind noise overpowers car noises for you.
It's been interesting to see all the comments about this! Obviously it's struck a nerve...and danger aside, I'm happy to see a number of people less than thrilled about the idea of noisier hybrids and EVs. There has to be a better solution.
The 1865 act required all road locomotives, which included automobiles, to travel at a maximum of 4 mph (6 km/h) in the country and 2 mph (3 km/h) in towns and have a crew of three travel, one of whom should carry a red flag walking 60 yards (55 m) ahead of each vehicle.
Backup audible warning is already implemented on most trucks, commercial vehicles, municipal vehicles, etc. That is not a bad idea; the driver has limited view, and risk is higher. But that is totally different than always on noise generators.
A new method of modeling how they are created with chemical vapor deposition (CVD) could reduce the cost of carbon nanostructures used for for research and commercial applications, including advanced sensors and batteries.
BMW has already incorporated more than 10,000 3D-printed parts in the Rolls-Royce Phantom and intends to expand the use of 3D printing in its cars even more in the future. Meanwhile, Daimler has started using additive manufacturing for producing spare parts in Mercedes-Benz Trucks.
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