For a public service vehicle (bus), it is illegal to follow another bus or truck on a highway closer than:

The legal requirement to maintain a certain distance when following another bus or truck on a highway is primarily for safety reasons. Being at a distance of 90 meters ensures that there is sufficient space to react to any sudden stops or emergencies involving the vehicle in front. This distance allows for better visibility, particularly on highways where speeds are higher, and helps to reduce the risk of collisions.

Maintaining a safe following distance enhances overall road safety, allowing drivers in public service vehicles to brake in time, maneuver safely, and manage any hazards that may arise. This rule is particularly emphasized for larger vehicles like buses and trucks due to their weight and longer stopping distances compared to lighter vehicles.

The other distances listed would not provide the same safety margin, as they either fall short of the recommended space required to react effectively or could contribute to unsafe driving behavior by encouraging closer following. Thus, the choice of 90 meters aligns with safety regulations aimed at protecting both the vehicle occupants and other road users.