Federal Motor Vehicle Safety Standards require that automotive parking brakes be capable of holding a vehicle stationary on a ________ degree grade

The correct answer denotes that federal regulations require automotive parking brakes to hold a vehicle stationary on a 30-degree grade. This standard is in place to ensure that vehicles can remain securely parked on various inclines without rolling away, which is especially important for safety in everyday situations where parking may occur on hills or slopes.

A parking brake that can reliably hold a vehicle on this incline means that it provides sufficient force to resist gravity's pull, ensuring the vehicle does not move unintentionally. This is critical for preventing accidents and ensuring the safety of passengers and bystanders. Understanding grade measurements allows vehicle designers and manufacturers to meet safety requirements, thereby protecting users on the road.

The other options, while they may seem plausible, contest the practical requirements set forth by vehicle safety standards—most notably, a vehicle's parking mechanism must effectively manage steep incline scenarios typical of urban and rural landscapes.