City Clerk
Director - Mark Houghton
City Of Manteca

SR120 / Union Road Interchange

​​​​The City of Manteca is working with Caltrans and SJCOG to improve safety at the interchange of Union Road and State Route 120.

This will be 1st Diverging Diamond Interchange (DDI) in California.

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The City of Manteca in partnership with Caltrans District 10 and SJCOG are working to improve safety and traffic flow at interchange located at State Route 120 and Union Road. 

The project will improve safety conditions by constructing new on & off ramps, widening Union Road to 4 lanes between Daniels Street and Lifestyle Street and will provide a Class I shared use path and Class II bike lanes.

The new interchange reduces conflict points between vehicles and moves traffic more efficiently through the interchange. The DDI is unique in that traffic on the local road is shifted to the left side of the road, before being shifted back to the right. Eliminating any left hand turns through the intersection.  Upgrading to the unique DDI configuration provides significant cost savings and safety benefits for both vehicles and pedestrians.

Union Road is a key crossing of State Route 120 in the City’s bicycle master plan. The new Class I path will provide a 12-foot wide grade-separated trail that eliminates all bicycle/vehicle conflict points within the interchange to provide safe and efficient passage for bicycles, pedestrians, and other non-motorized travel.

Benefits of a Diverging Diamond Interchange (DDI)

  • Cost effective solution allows for the project costs to be greatly reduced compared to other interchange types. This also allows for the existing bridge to remain.

  • Improved traffic operations on Union Road. This project will also construct auxiliary lanes on State Route 120 from Airport Way to Main Street.

  • Compact footprint by eliminating right of way acquisition.

  • Class I grade separated shared use path improves pedestrian and bicycle mobility. This accomplishes the City's General Plan goal and closes a significant gap in the pedestrian network.

  • Safety is highly increased with a DDI. There are reductions in collision points and added safety to bicycles and pedestrians. 


Key Project Elements

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  • ​Provide Pedestrian Access
  • Provide Bicycle Access
  • Reduce Traffic Congestion
  • Reduce Conflict Points

Safety is a priority.  

This Diverging Diamond Interchange will reduce the number of conflict points from the existing 26 down to 14.  Most importantly, the more severe collision types (crossing/T-bone) are reduced form 10 down to two.


The existing overpass does not have designated pedestrian or bicycle access. The new interchange will and provide a Class I shared-use path and Class II bike lanes. The new Class I path will provide a 12-foot wide grade-separated trail that eliminates all bicycle/vehicle conflict points within the interchange to provide safe and efficient passage for bicycles, pedestrians, and other non-motorized travel.  Auxiliary lanes will be constructed between Airport Way and Main Street on eastbound and westbound State Route 120


City of Manteca
San Joaquin Council of Governments  (SJCOG)

Shared Funding for this project is provided by City of Manteca and SJCOG.



Construction Schedule


​June 25, 2019
​Groundbreaking Event
​July 9, 2019
​Construction Begins
End of 2020
Projected Completion


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Manteca Bulletin Article:
March 1, 2019 - Better ByPass Movement

ABC10 Article:
July 11, 2019 - First of its kind interchange in California will be built in Manteca

 Construction Alerts:

  1. Work will generally take place between 6 a.m. - 5 p.m.  Monday through Friday. Night and/or Weekend work may occur as necessary

  2. Traffic Detours and Closures will be posted in advance on the City of Manteca Website Project Page and the City of Manteca Facebook Page.

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Weather permitting, SR120/Union Rd Interchange construction will begin Monday, July 8th.  We are expecting recurrent lane/shoulder closures and one lane reversing traffic control in the project area.   The lane closures will continue intermittently throughout the 1-year construction and will typically take place between 6:30am and 5:00pm Monday through Friday, with the full roadway being re-opened each afternoon.  Emergency vehicles will be allowed through the construction site and we will have a plan for traffic control personnel to follow in the event that these vehicles need to pass through during the lane closure.


Photo Documentation

Overhead View 2019
Groundbreaking CeremonyDuringRenderings



Project Manager:  Koosun Kim

Main Office Line: 209 456-8400