Mill Avenue Bridge

The Mill Avenue Bridge is a concrete open spandrel deck arch, which was built in 1931. It was the largest bridge in Arizona when it was built. This bridge is one of the oldest automobile crossings on the Salt River and has operated continuously since it opened. This bridge was a vital part of U.S. Route 89, which was the only north-south highway in Arizona prior to the inception of the freeway system in the 1950s.

The bridge was strategically designed to have aesthetic appeal while also being strong and durable. The ribbed arches with open spandrels give the bridge an elegant appearance, while also providing structural efficiency. The bridge is fully anchored in bedrock, which avoided the problems with the caliche soils that plagued many of the other bridges in the area. The Salt River tended to flood, especially during monsoon storms. This bridge was one of the few bridges that would remain open due to its structurally sound design and construction. In fact, a storm in 1980 closed all but two bridges due to safety concerns (The other bridge was the Central Avenue Bridge in Phoenix).

Dams were built in the Salt River in the early 1900s, which left the waterway dry, except during flood events. As traffic volumes grew, this bridge was converted to carry southbound traffic, and an at-grade road was created across the dry river to carry the northbound traffic. However, this crossing was frequently closed due to flooding, so the New Mill Avenue bridge was built adjacent to the existing bridge in 1993 and continues to carry the Northbound traffic.

This bridge was built to replace the previous bridge, which was built in 1913 and quickly became inadequate for the increasing traffic demands. This is also the location of Charles Hayden’s ferry service, which operated from 1874 until the dam was built in the early 1900’s, then continued to operate in times of flooding until the new bridge was built in 1993.

In 1999, a second dam was created to the west of the bridge to form the Tempe Town Lake. Water once again collected under the bridge, converting it back to its original look.