What is the best assumption to make about posted clearance heights when approaching bridges and overpasses?

When approaching bridges and overpasses, the best assumption to make about posted clearance heights is that they may be inaccurate. This consideration is crucial for drivers, especially those operating commercial vehicles like trucks and buses, which can vary significantly in height.

Clearance heights are determined by a couple of factors, such as the original construction specifications, maintenance work done over the years, and the possible presence of obstructions like road surface changes or snow buildup. Over time, adjustments may not always be made to the signage, leading to discrepancies between the posted height and the actual clearance available.

Therefore, it's important for drivers to remain cautious and consider that the posted heights could be different from what they perceive. This acknowledgment helps prevent accidents, such as a vehicle colliding with a bridge or overpass due to underestimating the required clearance. Always erring on the side of caution by verifying clearance before proceeding can avert potential damage and ensure safety on the road.