Design Truck is defined as which of the following?

• A. A pair of axles of 25-kip load and spaced 4 ft apart. The transverse spacing of wheels shall be taken as 6 ft.
• B. A single axle carrying 50 kips with 8 ft spacing.
• C. Three axles with 15 kips each, spacing 6 ft.
• D. Uniform load of 0.64 kip/ft along the length.

Answer: (A)

Design Truck is the standard vehicle loading pattern used in bridge design to represent heavy traffic. It uses two axles with equal loads of 25 kips on each axle, and the axles are 4 feet apart. The transverse spacing of the wheels is taken as 6 feet. This configuration is chosen because it provides a realistic and conservative loading that creates meaningful bending and shear demands on girders, while remaining a common and widely used reference pattern. The other patterns don’t fit this standard because a single 50-kip axle doesn’t capture the effect of a second axle, three axles with 15 kips each changes both total load and distribution away from the typical design truck, and a uniform load does not represent the concentrated nature of a moving vehicle.