What those gaps along highway bridges are really designed for – Jalopnik

Those potholes on highway bridges are more than just jarring moments that make your car thump (and can worsen the symptoms of wobbly suspension), they are crucial to maintaining the bridge’s structural integrity. So how can deliberately adding rattling potholes to a road actually improve infrastructure reliability while providing an added thrill by scaring the hell out of motorists? Allow us to explain.

These gaps are how bridges and other structures deal with thermal expansion so they can remain structurally reliable. This has to do with the way concrete, steel and other materials respond to extreme temperature changes, and those gaps (commonly called expansion joints) help compensate for the expansion or contraction of the materials. Bridges can stretch very slightly in warm weather, but they can also shrink or contract when the mercury drops. Without expansion joints, there is little room for the concrete slabs to expand or contract, which is not a good thing since expansion joints carry most of the stress in any structure, especially long-span bridges.

When expansion joints fail and the concrete expands due to excessive heat, terrible things can happen, including buckling the concrete slab and launching a poor Corolla into the air as if it were on a rally track. But when they work, the bridges are fine. That’s why in February 2026, the Texas Department of Transportation responded to social media posts from residents about holes in the overpass from US Highway 290 West to South I-35 by X“The viaduct is structurally sound,” and the holes are nothing to worry about as they are there for a purpose.

Short and medium span bridges typically have shear plate or compression seal connections using elastomeric foam and internal lattices. Long span bridges usually have finger plate or finger expansion connections using steel finger plates, rubber plates and anchor bolts. Engineers select expansion joints based on the expected ‘movement’ or thermal expansion of the material and are classified accordingly as minor movement (less than 45mm of movement), medium movement (45 to 130mm) and major movement (greater than 130mm).

As for that slightly unnerving “thud” you hear when driving over bridge expansion joints, it turns out that some are better than others at providing a quieter, almost seamless transition between the concrete surfaces. Tests have shown that wider gaps between bridge expansion joints produce more noise, and modular joints used in high-movement bridges tend to be noisier than the finger-plate expansion joints in medium-movement bridges.

Roads and bridges in the US have been in disrepair for years, but things have been improving since the American Society of Civil Engineers U.S. Infrastructure Report Card 2025 from a C- in 2021 to, um, just a C, which is still better than 2017’s D+.