In life, most adults regularly participate in one of the most dangerous activities they can, and that is none other than driving a vehicle. This vehicle weighs several thousands of pounds and can travel at quite high speeds. An object of such weight moving at such a speed contains massive amounts of energy. Hitting organic matter such as animals or other people will result in massive damage to whatever it is that gets hit.
This means that those that are driving, and also those that around vehicles or other drivers, should not engage in risky moves. A cyclist in a bike lane should not be doing anything risky, as falling could mean getting ran over by a vehicle.