Riding directly alongside another vehicle is discouraged because:

Riding alongside another vehicle is dangerous because you could be riding in the vehicle's blind spot. The driver may enter your lane without warning if they can't see you. The vehicle will also block your route of escape if a hazard arises.

• You may have a difficult time getting to a highway exit.
• You may be in the other vehicle’s blind spot.
• You may block the driver's view.
• It prevents other drivers from passing both of you.