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Lathrop plans for diverging diamond at Louise & I-5
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Lathrop might become the third city in the South County with a diverging diamond interchange.

With work currently underway in Lathrop to widen River Islands Parkway – the section of what once Louise Avenue from I-5 west across the San Joaquin River and into the master planned community of the same name – the City of Lathrop is completing steps that are part of the plan to overhaul the Louise Avenue interchange to better accommodate traffic in the area.

While the interchange currently has a traditional layout, the decision was made by the council to pursue a diverging diamond interchange – which inverts traffic patterns to maximize space – as part of an effort to reduce overall costs and the need to acquire right-of-way to complete the work.

“Recent and planned development in the area require that improvements be made to the Interstate 5/Louise Ave interchange,” the CIP Plan on the City of Lathrop’s website reads. “This interchange serves residential, commercial, and industrial development on both sides of Interstate 5, including Mossdale, Central Lathrop, River Islands, and Crossroads.

“Improvements to the interchange would provide enhanced traffic operations, air quality benefits, increased goods movement, improved safety and better pedestrian and bicycle mobility.”

The City of Manteca became the first in the South County — and California — to open a diverging diamond interchange when it cut the ribbon in November 2020 to  the new Union Road interchange on the 120 Bypass

Such an interchange allows for traffic that is entering the freeway to turn left onto the freeway without the need for a controlled intersection – improving the overall flow of traffic while eliminating conflict points, thus improving safety.

While the plan for the CIP is listed on the City of Lathrop’s website and work is being completed to make the interchange possible, the city is listed according to its timeline to begin construction this year – something that is not likely given the high price tag and the collaborative work necessary with the California Department of Transportation (Caltrans). 

To date the City of Lathrop has allocated nearly $5 million to complete the preliminary work necessary to make such an interchange possible.

A new diverging diamond, the second in the state, is being built in Tracy at the Interstate 580 interchange at International Parkway at the west edge of town as part of a nearly $53 million project to reduce traffic congestion and improvement movement of goods to area highways.

The International Park of Commerce is 450 acres and 20-million-square-feet of business park for fulfillment center, distribution, flex office and warehouse space and along with the Patterson Pass Business Park is home to businesses including Amazon, Costco, Safeway Medline, Smucker’s and FedEx Ground.

Ceres is also moving toward ground breaking of a diverging diamond interchange at Hatch Road and Highway 99.

Manteca — if everything goes to plan — will one day boast three diverging diamond interchanges all-in-a-row along the 120 Bypass.

Manteca city leaders made a pitch for federal funding to help cover the design work needed to start moving a diverging diamond interchange forward on the 120 Bypass at Airport Way.

It was part of the San Joaquin County One Voice regional effort in Washington, D.C., to promote projects with key federal officials for potential funding assistance.

It would be almost a carbon copy of the diverging diamond interchange at Union Road and the 120 Bypass a mile to the east.

Eventually, the city also wants to convert the existing Main Street interchange into a diverging diamond as well.


To contact Bulletin reporter Jason Campbell email