Bridges have weight limits primarily due to the stress and strain that heavy vehicles can impose on their structures, which can lead to localized failures even if the overall weight is within limits. The distribution of weight across multiple vehicles, as seen with rush-hour traffic, differs significantly from that of a single heavy truck, which can create concentrated stress points. Factors such as the design of the bridge, the potential for transverse stress from trucks not traveling in a straight line, and the condition of the road surface beneath the tires also play critical roles in determining weight limits. Additionally, while some large bridges may not display weight limit signs, they still adhere to general road weight restrictions, which can be stricter for certain structures. Understanding these dynamics is essential for maintaining bridge safety and integrity.