Main Street Bridge, Railway bridge in Hillsboro, United States.

Main Street Bridge is a concrete tied-arch bridge in Hillsboro, Oregon, carrying MAX Blue Line light rail over Main Street and 18th Street. Completed in 1997, it is 425 feet (130 m) long, with a reinforced concrete arch 110 feet (34 m) wide and 75 feet (23 m) tall straddling the roadway in place of a center pier. Six cables, each four inches (102 mm) in diameter, run from the arch to the bridge deck, and a post-tension tie beam connects the arch ends underground.

The structure was built in 1997 and replaced a wooden trestle from 1917 that was removed after freight service ended in 1977. This new design reflected the need for a modern crossing suitable for contemporary light rail operations.

The final pieces of track for the Westside light rail line were installed on this bridge in October 1997, where the project's "golden spike" was driven. Passenger service on the $964 million line began on September 12, 1998.

The bridge sits between the Washington/Southeast 12th Avenue and Hillsboro Airport/Fairgrounds stops on the MAX Blue Line, so riders cross it in about a minute. To see the arch and its six cables from outside, walk or drive along Main Street near 18th Street rather than from the train. The span crosses what is planned as five lanes of traffic.

The design intentionally avoids central support columns to create a completely clear span across the corridor. This engineering choice was driven by safety concerns related to accidents that had occurred with previous crossing structures at the same location.