Which of the following is not typically included in a bridge's substructure?

The substructure of a bridge primarily supports the superstructure and transfers loads to the foundation. Typical components of a bridge's substructure include piles, footings, and abutments.

Piles are deep foundation elements driven into the ground to provide stability, especially in soft or unstable soil conditions. Footings distribute the load from the bridge's superstructure to the ground and are crucial for the overall stability of the structure. Abutments support the ends of the bridge and retain the soil or other materials behind them.

Barriers, on the other hand, are generally considered part of the bridge's superstructure or its ancillary elements rather than the substructure. Barriers are designed for safety, preventing vehicles from falling off the bridge or encroaching into pedestrian areas, but they do not contribute to the structural support of the bridge itself. This distinction clarifies that barriers are an essential component for safety but do not play a role in the load-bearing function of the bridge's substructure. Therefore, the correct response identifies barriers as not typically included in a bridge's substructure.