What is the significance of considering side friction in traffic flow?

Considering side friction in traffic flow is crucial because it significantly impacts both the capacity and safety of the road. Side friction refers to the lateral forces exerted by vehicles interacting with their environment, which can include pedestrians, cyclists, roadside parking, and other roadside features. These interactions can reduce the available roadway width for vehicles, especially in situations where vehicles cross into lanes or when there's an obstruction.

When side friction is taken into account, it helps engineers to determine the effective lane width needed for safe vehicle movement. This, in turn, influences how many vehicles can safely navigate a given road section—essentially impacting the road's capacity. Roads with excessive side friction can lead to reduced speeds, increased likelihood of accidents, and overall unsafe driving conditions. Therefore, understanding and managing side friction is vital for creating safe and efficient roadways that accommodate the expected traffic flow while minimizing risks to all road users.