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After river span is replaced, work will start on 120 Bypass/99 interchange 6 months later
The aging southbound Highway 99 bridge that is being replaced.

The 206-foot long aging arch span on southbound Highway 99 across the Stanislaus River is being replaced with an $18.2 million new bridge thanks to the 2017 gas tax hike.

While the project started in April, work will pick up in the coming weeks with crews working day and night as well as Saturdays and Sundays. Lane shifts have been implemented to allow for three open traffic lanes for northbound and southbound traffic during construction.   

Work is expected to be completed by December 2020. Highway 99 motorists will deal with construction free travel between the 120 Bypass and Stanislaus County for about six months after the bridge work is completed. Caltrans plans to start the first phase of improvements to the Highway 99/120 Bypass interchange as well as the Austin Road interchange in the summer of 2021.  The first phase of the project will be completed in the fall of 2023.

The Highway 99 replacement span won’t be the only new bridge crossing the Stanislaus River at Ripon that will be built through the 12 cent gas tax hike. As part of the deal to get Senate Bill 1 passed, funds were committed to extend Altamont Corridor Express passenger service south to Ceres. This will require double tracking the Union Pacific line from Lathrop though Manteca, Ripon, and Modesto. It will require a second train trestle across the Stanislaus River.

The Highway 99 work is in addition to a another Senate Bill 1 project starting the week of June 16 on segments of Interstate 205 and Interstate 5 in San Joaquin County to extend the life of 18 bridges at a cost of $2.9 million

“SR-99 is a vital trade route that endures much wear and tear,” said Caltrans Director Laurie Berman. “This SB 1 project will allow crews to make immediate improvements to provide a safer commute for motorists, while improving this busy freight corridor.”

The Stanislaus River bridge replacement project will benefit commuters traveling between the cities of Manteca, Ripon and Modesto, as well as truckers hauling commercial and agricultural goods to the businesses throughout San Joaquin County and beyond. Each day more than 129,000 motorists and 17,400 truckers use the segment of Highway 99 crossing the river.

M.C.M. Construction, Inc., of North Highlands is the contractor.

 The work schedule is subject to change due to traffic incidents, weather, availability of equipment and/or materials, and/or construction-related issues. More information and updates on projects can be found at or on Twitter via @CaltransDist10.  

SB 1 provides an ongoing funding increase of approximately $1.8 billion annually for the maintenance and rehabilitation of the state highway system. SB 1 funds will enable Caltrans to fix more than 17,000 lane miles of pavement, 500 bridges and 55,000 culverts by 2027.

To contact Dennis Wyatt, email