Built in 1964, the Hickman Road Bridge over the Tuolumne River in Stanislaus County, Calif., provides a vital link between the community of Hickman and the city of Waterford.

However, since 1997, stakeholders with an interest in the bridge have been looking for a way to retrofit or replace the nearly 60-year-old structure with something that would benefit multimodal vehicles. As the project continued, it would be lauded by the League of California Cities (Cal Cities).

Critical care

          When it was originally constructed in the mid-1960s, the Hickman Road Bridge was a seven-span concrete box girder with concrete abutment and pier walls supported on pile caps founded on driven piles. After nearly six decades of service, it was determined that the bridge was scour critical, and during high storm events — when the river levels are elevated — the structurally deficient passage had to be closed.

          “The closures were a major inconvenience to the traveling public as the detour was substantial at over 10 miles,” said Sam Chrun, PE, deputy director of engineering services for the Stanislaus County Public Works Department.

          With an average daily traffic rate of 6,441 vehicles and no practical solution to repair the failing bridge, city and county officials commissioned Dewberry — a nationwide firm of design, planning and construction professionals — to create a new one. It would be a massive, multi-million-dollar project, but luckily, the bridge’s scour critical status and the fact that the bridge did not meet existing seismic design criteria meant it was eligible for replacement under the Highway Bridge Program (HBP) and Local Seismic Safety Retrofit Program (LSSRP). Additional funding was procured from the Measure L Local Street & Roads Funds, city of Waterford and Highway User Tax Account Funds for a grand total of $24 million.

          The new bridge consists of a 750-foot-long cast-in-place, post-tension box girder that is supported by seat abutments at each end and intermediate two-column piers. Each pier is supported by two large diameter cast-in-drilled-hole piles ranging in 100-125 inches in diameter and up to 125 feet in depth to address the ongoing degradation of the Tuolumne River channel. It also features two 12-foot-wide travel lanes; two 8-foot-wide shoulders; and one 5-foot-wide sidewalk along the east side of the bridge. It was immediately upstream of the existing structure, keeping the existing road and bridge open to the public during construction. The result is a bridge that is wide enough to accommodate two lanes of vehicular traffic plus safe pedestrian and bike access.

          “The bridge had to be closed for approximately two weeks to construct the needed improvements to divert traffic from the old to new bridge,” Chrun said. “The existing bridge was then demolished upon completion of the new bridge construction.”

New features and improvements

          Besides the safer structure and multimodal features, the Hickman Road Bridge replacement project included the installation of a 16-inch PVC water main in the bridge to provide the community of Hickman a future sustainable and reliable water supply from the city of Waterford. Project leaders also addressed the ongoing degradation of the Tuolumne River channel and made improvements to the local environment by minimizing the number of bridge foundations in the Tuolumne River channel. This mitigated the number of plants that had to be uprooted while also preserving the look, function and feel of the River Park and the River Park Trail.

          Construction required the temporary closure of the River Park and a portion of the River Park Trail to provide access for the heavy machinery needed to build the new Hickman Road Bridge. As the project concluded, contractors reestablished and made improvements to the spaces that will have permanent impacts within the community.

          “The River Park Trail was rerouted to a more level, ADA-compliant path of travel with proper retaining walls and hand railing through the site,” Chrun said.

As part of the California Department of Fish and Wildlife environmental permitting requirements, the team also had to mitigate for any loss of habitat that the bridge project might impact. As it turned out, there was an estimated 6,000 bats living on the old bridge in the gap between the exterior bridge girder and the telecommunication conduits on the upstream side of the bridge. During construction, the crew could maintain the bat colonies on the old bridge while the new one was being built during the first year of construction. When the bats migrated south for the winter, crews excluded the bat habitat on the old bridge and incorporated bat houses in the new structure so when they returned in the spring, the mammals could move into their new abodes.

“This was extremely successful since the new bridge has a thriving bat colony,” Chrun said.

Award-winning project

          The Hickman Road Bridge replacement project has been so successful, it was the overall winner of the 2023 Outstanding Local Streets and Roads Project Awards, which recognize creative and cost-efficient programs in counties and cities throughout California that preserve and protect the public’s investments in improving local streets, roads and bridges.

          Sponsored by Cal Cities, County Engineers Association of California and California State Association of Counties, the Outstanding Local Streets and Roads Project Awards were awarded to five innovative programs during the Cal Cities Public Works Officers Institute/CEAC Spring Conference on March 9 in Los Angeles County.

          “Every day, cities and counties are delivering on important transportation in their communities,” said Cal Cities Department of Public Works President Benjamin Fine, Pismo Beach director of public works and city engineer. “These award-winning projects demonstrate local leaders’ commitment to reducing greenhouse gas emissions and the vital role local jurisdictions play in achieving our state environmental goals.”

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