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California’s first diverging diamond interchange nears completion as mayor pushes for two more
union road ribbon cut
Flanking Mayor Ben Cantu as he prepares to cut the ribbon to dedicate the new Union Road interchange are council members Jose Nuño, left, and Debby Moorhead.

Twenty-five years ago you could not exit or enter the 120 Bypass from the Union Road overpass.
No ramps were put in place at Union Road when the Bypass opened as a hybrid three-lane highway/freeway in the 1980s. Ramps weren’t added until the mid-1990s when the 120 Bypass was widened to its current four-lane configuration.

Once Wednesday rolls around, Union Road will reopen to traffic as California’s first diverging diamond interchange — a design where overpass traffic crosses each other to  improve traffic flow and reduce conflict points for potential accidents. It is an improvement that in the realm of freeway element design is light years away from the original bridge-only crossing when the Bypass opened to connect with a bumpy narrow two lane road lined up to the freeway’s edge with orchards and pasture.

“We still have two more to do,” Mayor Ben Cantu said of future diverging diamond interchanges along the 120 Bypass. “I would like to really get that done in 10 years. As long as I’m on the council I’m pushing for that. I want Manteca to be the first to have three (diverging diamond interchanges) in the same community in this country.”

The city has preliminary committed to using the diverging diamond interchange (DDI) approach when they go to widen the congested Airport Way and Main Street overcrossings. Besides the safety and improved traffic flow touted by Caltrans District 10 Director Dennis T. Agar, the DDI design doesn’t require the taking of additional property. It is quicker to build and less costly given the existing bridge structures can be incorporated into the new design. Going with the DDI design at Union Road saved nearly $10 million over a more traditional diamond interchange.

Cantu and Agar made their remarks Thursday in the front parking lot of the Union Road fire station. That is where dignitaries gathered for an official ribbon cutting of the project that opens to the public next Wednesday.

Assemblyman Heath Flora’s field representative Jason Laughlin, who grew up in Manteca, pointed out that the Union Road project could also be another rarity for California — a freeway project that even with its accelerated construction timeline and lower cost managed to come in under budget by $150,000 as well as open four months ahead of schedule.

“Under budget and early — that’s incredible,” Laughlin noted.

Although most of the $23.7 million tab was essentially the last major hurrah project for the now defunct Manteca Redevelopment Agency, the countywide Measure K half cent sales tax for transportation projects voters passed in 1990 and extended in 2006 played a pivotal role in making the project happen.

San Joaquin Council of Governments Executive Director Andrew Chesley noted $1 million from Measure K kept the project moving forward when PG&E slapped the city with an unexpected $1.8 million bill after the project bid was awarded to relocate four transmission lines they normally pick up half the cost on and the state the other half.

SJCOG also awarded funds for the separate bicycle/pedestrian bridge crossing — the first on the 120 Bypass —  that were fused with RDA funds to pay for the interchange work.

Councilman Gary Singh — who emphasized the safety, reduced accidents, smoother traffic flow, and cost savings — said he expects motorists will adjust to the design even with it involving “driving on the wrong side of the road” for a brief period.

Singh also pointed out an aspect of the project that dovetails into efforts he has pursued to improve pedestrian safety in Manteca. Union Road is now the only crossing of the 120 Bypass where sidewalks extend to and over bridge decks. You can now take a sidewalk — interrupted with street crossings — all the way from the northern city limits past the last entrance to Del Webb at Woodbridge to Woodward Avenue.

Neither the Main Street nor the Airport Way overcrossings have sidewalks leading up to them or on the bridge deck. There is not only no separation from vehicle traffic but the only barrier along the bridge is a three-foot concrete K-rail style structure as opposed to a chain link fence that is standard on most California freeway overcrossings that see substantial foot traffic.

The project also adds auxiliary lanes on the 120 Bypass in each direction from Union Road connecting with ramps at both Main Street and Airport Way.

Those lanes will allow smoother merging with Bypass traffic as well as help reduce peak congestion as motorists wishing to exit the freeway to be able to move over earlier.

As speeches were being made, crews on the  southwest corner of the interchange were putting pre-poured concrete walls in place for the 116,641-square-foot Living Spaces furniture showroom. It is the first of several commercial projects expected to move forward with the upgraded interchange in place.

To contact Dennis Wyatt, email