Most highway bridges have expansion joints so the bridge can safely expand and contract without cracking, warping, or breaking under temperature changes and loads.

Core reason

  • Bridge materials like concrete and steel expand in heat and contract in cold, changing the bridgeā€™s length over the day and across seasons.
  • Expansion joints create controlled gaps that let sections move back and forth instead of building up internal stress that would cause cracks or structural damage.

What the joints actually do

  • They allow longitudinal movement (back-and-forth along the length of the bridge) from temperature changes, shrinkage of concrete, and creep, so the deck does not tear itself apart.
  • They also help accommodate other movements from traffic loads, vibration, settlement, and sometimes seismic effects, keeping the bridge alignment and surface usable for vehicles.

Why they are essential for highways

  • On long highway bridges, the total expansion can reach centimeters to tens of centimeters; without joints, this would lead to serious cracking, buckling, or ā€œbending out of placeā€ under extreme conditions.
  • Expansion joints also help transfer loads between bridge segments while maintaining a relatively smooth driving surface, so traffic can pass continuously even as the structure moves slightly.

Short answer version

Most highway bridges use expansion joints so the structure can ā€œbreatheā€ with temperature and load changes, preventing cracks and distortion and keeping the bridge safe and durable over its lifetime.