HOV Bridges Hurdle Obstacles

Stanley Consultants designs a one-of-a-kind bridge that reduces the size and cost of a Phoenix, Arizona bridge for a project that is a showcase of engineering innovation and ingenuity.

Adjusting to Phoenix's growth and congestion, the Arizona Department of Transportation, along with design by Stanley Consultants, extended seven miles of High Occupancy Vehicle (HOV) lanes along the SR 51 corridor, connecting its completed link to the SR 101L.

The original design concept, developed by another engineering firm, called for a simple and straightforward, but very expensive "fly-over" connector bridge. Stanley Consultants' idea reduced the bridge length by 33 percent and reduced costs by $5.5 million.

The freeway-to-freeway HOV ramp connectors required inherently complex bridges. Stanley Consultants configured the precast prestressed concrete fly-over bridges using only two specified lengths for all spans. Design and construction was simplified by using three nearly identical, level, post-tensioned straddle bents to carry the bridges over the freeway. However, each straddle bent supports only one of two bridges passing over it. Pedestals constructed atop the straddle bents transfer just one superstructure load to the substructure. The other superstructures do not touch. This clever separation technique is the first of its kind.