It’s called an e-bike, power-assisted bicycle (Canada), power assisted cycle (UK), electric pedal assisted cycle (EU), motor-driven cycle (Alabama), motorized bicycle (Washington DC), low-speed bicycle (Illinois), bicycle with helper motor (Connecticut) or simply electric bicycle.
Reaching legal speeds up to 35 mph (though generally closer to 20 mph), electric bicycles are an option for many commutes. They can be pricey- up to about $3000-, but there are plenty of conversion kits on the market to turn your conventional bike electric.
In this video, Matt Dieckmann of Electric Race Bikes showed us the “pit bike” he rigged together using a 72 volt kit and zip ties. Conversion kits consist of a motor, a controller and a throttle (“the controller takes your throttle input and modulates that power to the brushless motor”).
Matt explained that electric bikes have really become viable in the past 5 years with the advances in lithium battery technology. Lithium batteries are much lighter than lead-acid so his bike rigged with a 4 cell lithium polymer pack only weights about 70 pounds instead of the well-over 100 pounds of a bike with a lead-acid setup.