I found this bridge referenced in Structurae. It was built in 1989, it has a 10.5 m (34.5 ft) wide deck, and it was build by incremental launching. We saw this technique used to build the Pont Charles de Gaulle in my blog of April 11, 2009. Although that was a steel bridge, the technique is similar. Box girder segments were cast behind the abutment, cured, and then pushed out with hydraulic jacks. It seems incredible to me that this 1/4 mile long bridge could be pushed out from one abutment! It must have had a very high camber to have been cantilevered out so far without deflecting below the top of the pier!
A short article on incremental launching of bridges provided by the University of California at Berkeley is available on the Internet. It looks as though a special nose is put on the end of the superstructure to help it get over the piers.
Note the squat bearings between the top of the piers and the bridge soffit. The superstructure must be able to slide on these bearings as it is pushed out across the canyon. Also note the rebar sticking out of the side of the superstructure. There must be a vertical diaphragm, perhaps at the end of each segment. I imagine each precast segment was pushed out and then post-tensioning tendons were attached to the next piece, which was also pushed out, until a completely post-tensioned superstructure reaches the other side of the canyon.
Mexico's Bridges: Puente Atenquique II (2) by Mark Yashinsky is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 United States License.