The bridge is a post-tension box girder structure with the center pier as an arch support straddling the road.[2] Used in lieu of a center support, the arch is 110 feet (34 m) wide[2] and 75 feet (23 m) tall.[3] Six cables measuring four inches (102 mm) in diameter run from the arch to the main structure of the bridge at the center.[3] The two ends of the reinforced concrete arch are connected to each other underground using a post-tension tie beam, making the structure a tied arch.[2]
History
After more than a decade of studies and designing, construction on the Westside MAX light rail line began in 1993.[4] In 1997, construction on the Main Street Bridge began. The bridge was designed by BRW to cross what is planned to be five lanes of traffic on Main Street.[3] The city of Hillsboro required the bridge to be able to cross over the planned widening of the roadway without using a center support column, so as to prevent the kind of accidents that had plagued a previous crossing at the same location,[3][4] a wooden trestle bridge of the Oregon Electric Railway, built in 1917 with a vehicle clearance height of just 10 feet, 6 inches.[5] After abandonment of freight service on the line in the mid-1970s, the city required the successor railroad, the Burlington Northern Railroad, to remove the old crossing, in 1977.[5][6] In September 1997, the construction of the current bridge structure was completed.[7] The "golden spike" of the Westside light rail line was driven with the final pieces of track of the project installed on this bridge in October 1997.[8] Passenger service on the $964 million project began on September 12, 1998.[8]
^ abcdArch support for Tri-Met extension; engineers in Hillsboro, Oregon, constructed a 75-foot-high (23 m) concrete arch over a roadway without using a center support, so that the arch can support bridge cables for the light rail overpass; Transit Update. Railway Age, November 1997 No. 11, Vol. 198; Pg. 27; ISSN0033-8826
