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California State Route 57 (SR-57) is a major north-south freeway corridor that provides commuters access to and from the San Gabriel Valley, portions of Los Angeles, San Bernardino, Orange and Riverside Counties. California State Route 60 (SR-60) is a major east-west freeway corridor that is parallel to and south of the Interstate 10 (San Bernardino Freeway) and links commuter and commercial travel to and from the San Gabriel Valley, Pomona Valley, San Bernardino and Riverside Counties to the Los Angeles Central Business District.

When the existing freeway interchange connecting SR-57 with SR-60 was designed, the underlying “Valley-shaped” terrain forced both freeways into a common alignment for a distance of 2-miles in the vicinity of Grand Avenue, referred to as the “Confluence”. A Freight Performance Measures Analysis of 30 Freight Bottlenecks conducted by the American Transportation Research Institute in ranks the Confluence as the #7  bottleneck in the Nation and #1 for freight delays and truck accidents in California.


More than 356,000 commercial and personal vehicles use the interchange every day an average of 1 million vehicles every 3 days, or about 100 million vehicles annually.


The State Route 57 (SR-57) and State Route 60 (SR-60) area of confluence, between the City of Diamond Bar and City of Industry, is among the worst segments of freeway in the nation for traffic congestion and accidents. This two mile long area is also one of the busiest truck freight routes in the country, which adds additional stress and conflict as cars and trucks contend for position on the road. The 57/60 Confluence is used by more than 350,000 vehicles daily including an estimated 26,000 goods-carrying trucks. It is California’s most problematic truck bottleneck and ranks seventh worst in the nation, according to the American Transportation Research Institute. These highways are vital interregional freeways and freight corridors, critical to Southern California’s ports, intermodal facilities, warehousing, manufacturing, and export-dependent industries.


To improve the congested and hazardous 57/60 Confluence, the Project will reduce dangerous lane weaving movements by reconfiguring ramps and interchanges, and adding mainline and bypass lanes, thus improving commuter safety and reducing traffic congestion. In addition, the project will help alleviate supply chain challenges in the region.

Phase III Construction:

The SR 57/60 Confluence Chokepoint Relief Project Phase 3 started in July 2023 and is ongoing. Project completion is scheduled for July 2028. The total cost for the project is $444.12 million.

The 57/60 Confluence has been funded with a combination of Local, State, and Federal sources. Major construction of the SR 57/60 Confluence Chokepoint Relief Project began in July 2023 and is ongoing. The project is scheduled for completion in July 2028. 

The construction includes:​​​​

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New eastbound SR-60 Grand Avenue bypass bridge exclusively for eastbound SR-60 commuters exiting Grand Avenue.

New Grand Avenue bridge with reconfigured on- and off-ramps.

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New eastbound SR-60 bypass bridge over Diamond Bar Boulevard to be used as a bypass for eastbound SR-60 commuters.

New eastbound SR-60 bypass bridge over Prospectors Road to be used as a new lane on eastbound SR-60.

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