Yes, an overpass is a type of bridge. The difference is what it crosses over. A bridge typically spans water or a natural barrier like a valley, while an overpass carries traffic over another road or a railroad. Structurally, though, they share the same basic engineering: a deck, support piers, and abutments at each end.
What Makes an Overpass a Bridge
In engineering terms, any structure that carries a path over an obstacle is a bridge. An overpass fits that definition. It uses abutments to retain the embankment on each side and transfer loads down to the foundation, just like a bridge over a river would. The design requirements for those abutments are essentially the same as for retaining walls and piers on any other bridge.
Federal law treats them identically. The U.S. code directing the National Bridge Inventory explicitly includes highway bridges “over waterways, other topographical barriers, other highways, and railroads.” An overpass spanning an interstate gets the same safety inspections, on the same schedule, as a bridge crossing a river. The inspection standards are designed to ensure uniformity across all of these structures regardless of what’s underneath.
The Federal Highway Administration defines a bridge as any structure with an opening of more than 20 feet measured along the center of the roadway. If an overpass meets that threshold, it’s officially a bridge in the national inventory and subject to all the same reporting and maintenance requirements.
How the Terms Differ by Region
The word “overpass” is mostly a North American term. In the United Kingdom and other Commonwealth countries, the same structure is called an overbridge or a flyover. In North American usage, “flyover” usually refers to something more specific: a high-level overpass built above the main overpass lanes, or a bridge constructed over what used to be a ground-level intersection.
A related term you might encounter is “viaduct,” which generally describes a longer elevated road or rail structure carried on a series of spans, often crossing a valley or running through an urban area. Viaducts are also bridges, just longer ones with more support piers.
The Practical Differences
While overpasses and water-crossing bridges share structural DNA, they have some distinct design constraints. Highway overpasses must maintain a minimum vertical clearance so trucks can pass safely underneath. On rural interstate sections, that clearance is at least 16 feet across the full roadway width, including shoulders. Urban interstates follow the same 16-foot standard on at least one route, though other urban interstate routes can go as low as 14 feet.
Overpasses also need to maintain specific horizontal clearances and sight distances so drivers below can see approaching traffic and exits. These requirements don’t apply to a bridge over a river, where the concern is water flow and navigation rather than vehicle movement underneath.
Engineers choosing between an overpass and an underpass (where traffic dips below the crossing road or railroad) weigh several factors. One practical consideration: an overpass gives drivers an advance visual warning of a grade change ahead, while an underpass dips below grade in a way that’s less immediately apparent. Cost, drainage, and available right-of-way all factor into the decision as well.
Why the Distinction Matters
For everyday conversation, calling an overpass a bridge is perfectly accurate. The distinction is really about specificity. Saying “bridge” tells someone a structure spans a gap. Saying “overpass” tells them it spans a road or railway. It’s the same relationship as “vehicle” and “truck”: one is a subset of the other.
Where the distinction matters most is in navigation and local terminology. If someone gives you directions mentioning “the bridge,” you’d likely picture a crossing over water. “The overpass” immediately tells you to look for a road crossing above another road. Both are structurally bridges, but the words paint different mental pictures, which is why both terms persist.