Bridges, as vital infrastructure connecting opposite banks, require meticulous attention to safety considerations. Among these, live loads —the moving vehicle weights that must be accounted for in bridge design—play a crucial role in determining a structure's load-bearing capacity and service life. Imagine heavily laden trucks traversing a bridge day and night; without precise live load calculations, the structure would face significant safety risks.

Live loads are primarily categorized as Type A and Type B , differentiated by road classification and frequency of heavy vehicle traffic. Type A live loads apply to municipal roads where 25-ton trucks appear relatively infrequently. Type B live loads govern highways, national routes, provincial roads, and connecting municipal arteries—the primary thoroughfares for heavy traffic. Consequently, Type B specifications demand more rigorous design standards.

Engineers employ two principal calculation methods: T-loads simulate individual vehicle rear axle weights, with a contact area of 500×200 mm carrying 100 kN (equivalent to a 25-ton truck's rear axle). L-loads represent traffic group loads, where Type A and Type B calculations differ in their p1 load distribution lengths, as specified by relevant engineering standards.

A significant revision to bridge live load standards occurred in 1993, raising heavy vehicle capacity specifications from 20 to 25 tons. This update eliminated the previous first-class (T-20) and second-class (T-14) bridge classifications, replacing them with the current Type A/B system. The revised Type A standard corresponds to the former TL-20 load, while Type B aligns with TT-43 specifications—originally developed for 43-ton trailer loads on expressways. These changes substantially enhanced structural safety and reliability to accommodate growing transportation demands.

Precise live load calculations remain fundamental to bridge safety. Engineers must synthesize multiple factors—road classification, traffic volume, vehicle types—while applying Type A/B loads, T/L calculations, and current design standards. Only through such comprehensive analysis can structures reliably safeguard public safety and infrastructure integrity.