Which sign warns drivers about a low bridge ahead?

The sign that warns drivers about a low bridge ahead is the Height Restriction Sign. This sign provides crucial information about the maximum height permissible for vehicles passing under a bridge. It is designed specifically to inform drivers, particularly those operating tall vehicles such as trucks or buses, about the limitations they may encounter ahead. By indicating the height measured above the roadway, this sign helps prevent potential accidents or damage to vehicles that may not clear the bridge safely.

In contrast, the other signs mentioned serve different purposes. A Bridge Warning Sign typically alerts drivers to the presence of a bridge but does not provide specific information regarding height restrictions. A Construction Sign indicates road work or constructions activities, which can prompt changes in traffic flow but does not address bridge height. A School Zone Sign is intended to alert drivers to areas where children are likely to be present, indicating a need for reduced speed but again, is unrelated to bridge height. Hence, the Height Restriction Sign is the most relevant and appropriate for warning about a low bridge ahead.