The shoulder of a road is defined as that portion of the highway that is ______.

The shoulder of a road is defined as that portion of the highway that is contiguous to the roadway. This area is typically adjacent to the main travel lanes and is an extension of the road surface. Its primary purpose is to provide a space for vehicles that need to stop, for emergency situations, and to enhance safety for both vehicles and pedestrians.

The shoulder can serve multiple functions, including accommodating vehicles that run out of fuel, have mechanical issues, or need to pull over for any reason. It also aids in drainage and can serve as a buffer zone between vehicles traveling at speed and non-motorized users, like pedestrians or cyclists.

While shoulders can also be utilized for emergency purposes, and they may be designed in ways that allow for that, the key defining characteristic is their proximity to the roadway. This clarification helps in understanding traffic flow and road safety measures. Features such as solid lines or pedestrian access may influence their design or usage but do not define what a shoulder is fundamentally.