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Interchange design costs rise with seismic study
Service overpass 99
It will be years until there is movement to tear down the Service Road overpass and replace it with a wider one featuring a diverging diamond design. - photo by JEFF BENZIGER/ Courier file photo

The consultant drawing up designs for the new Mitchell & Service interchange with Highway 99 is now getting an additional $629,390 to do further work.

Since 2006, the city has spent over $9.5 million with NV5 (formerly Nolte & Associates) working on plans for the new interchange. The agreement has been amended 13 times to include additional work items associated with changed conditions and progress towards a final design.

Ceres City Engineer Kevin Waugh said the consultant now must do new work required to finish what is called the 95% PS&E (Plans, Specs and Estimates).  The PS&E is essential to facilitate construction, provide contract control, estimate construction costs, and provide a uniform basis for bidding purposes.

The new work includes a seismic analysis by engineering consultant Kimley-Horn, Service Road design modifications and surveys by O’Dell Engineering and additional traffic studies.

NV5 expects to be done with its work by July 2024 for the 95% PS&E.

Meanwhile, Waugh and his staff are preparing to seek out and hire a consultant to guide the city through the process of acquiring the rights-of-way needed to build the new interchange. Some properties on the east side of Highway 99 north of Service Road are needed to build a new northbound freeway onramp. The agent will oversee title and escrow services, prepare appraisals, meet with property owners, make offers on the city’s behalf, negotiate the transfer of ownership and provide relocation services of displaced residents if necessary. All the rights-of-way must be acquired by the city before the 100 percent complete PS&E document is submitted for Caltrans approval.

Waugh said the interchange project is expected to cost an estimated $211 million. The Stanislaus Council of Governments (StanCOG) has committed to cover $30 million from the half-cent sales tax measure passed by county voters in 2016. The city of Ceres has set aside $4.29 million for the project. A shortfall of $176.3 million would have to be covered by state and federal grants, said Waugh.

The existing interchange at Mitchell Road will be converted to a partial interchange, with a northbound off-ramp and a southbound on-ramp to Highway 99 and a replacement of the Mitchell Road undercrossing. The project includes an extended deceleration lane at the northbound off-ramp to Mitchell Road, and an extended acceleration lane at the southbound on-ramps from Mitchell Road and Service Road. There will also be the addition of auxiliary lanes between the Service Road interchange and the Fourth Street ramps.

Local roads affected by the project include El Camino Avenue, Rohde Road, Moffett Road, Don Pedro Road, Sixth Street, Ninth Street, Lucas Road and Brickit Court.

The interchange at Service Road will include a diverging diamond design similar to the one in Manteca. Normally a vehicle travelling westbound over a freeway overpass would be on the north side while eastbound motorists would be on the south side of the overpass. The diverging diamond flips that circulation pattern to allow for less traffic conflicts, better and increased traffic flow and better access to the freeway.

Diverging diamond diagram
The diverging diamond design for the new and improved Service Road overpass spanning Highway 99.