The world's first purpose-built hydrogen-powered bike has been released.

"The motorbike, known as an Emissions Neutral Vehicle (ENV), has a top speed of 50mph (80km/h), a range of at least 100 miles (160km) and can run continuously for four hours before the fuel cell needs recharging."

What's more, the bike's "exhaust" is water vapor and is so clean that its drinkable.
Concerns are that the bike is too quiet and plans have been made to add a motor sound to the bike so as to not startle pedestrians.

"For their part, manufacturers said the fake engine noise device, which could be switched off, would help alert road users."

I think they should develop custom 'fake engine noise' so that you can change your bike's noise on a daily or weekly basis. It would be cool to have your bike sound like a giant locomotive on one day and like the Jetson's flying car the next. When you think about it though it would also be cool to turn off all sounds and ride around in stealth mode.