Where cyclists ride on the road is often filled with debris kicked up by car tires. So it is not a rare occurance that they will need to swerve to avoid a rock

Where cyclists ride on the road is often filled with debris kicked up by car tires. So it is not a rare occurance that they will need to swerve to avoid a rock or stick, especially given the very narrow (23-25mm) tires commonly found on road bikes.