An update on construction sequencing, possible ramp closures, and detours connected with California’s first diverging diamond interchange being put in place at Union Road and the 120 Bypass is being provided at a community meeting taking place on Wednesday.
The Jan. 8 update being staged by the project team and city officials is set for on Jan. 8 from 6 to 7 p.m. at the Manteca Transit Center, 220 Moffat Blvd.
The project also entails building auxiliary lanes on the 120 Bypass from Union Road between both the Airport Way and Main Street interchanges. There will be a separate freeway crossing for bicyclists and pedestrians as well.
The diverging diamond design that has been used in other states with great success came about after elected city officials tasked municipal Public Works staff to come up with a solution to improve traffic movements through the Union Road and 120 Bypass interchange in the most efficient and cost effective way possible. The result — after an intense collaboration with Caltrans — was the diverging diamond interchange.
The $23.7 million interchange that employs a bridge deck where travel lanes cross each other twice will be used as a model for similar interchanges through the state including the second one that will be built at Highway 99 in Ceres and a third now being considered in the Los Angeles Basin.
It is also highly likely the design that will be used in the future when Manteca goes to widen the 120 Bypass overcrossings at Airport Way as well as Main Street given it does not require a bigger footprint and a taking of additional right of way and costs a third less than a conventional interchange project.
How diverging
diamond design works
With a diverging diamond interchange the flow across the freeway has lanes crossings to the opposite side of Union Road where the ramps are and then crossing back over at the ramps on the other side of the bridge.
Where the traffic crisscrosses they are traffic signals. On a traditional overpass turn movements on and off the freeway would also go through the traffic signals. That’s not the case with a diverging diamond interchange.
If Union Road was improved to a partial cloverleaf interchange as was originally envisioned there would be 24 conflict points for vehicles. The diverging diamond has 12.
Even more significant is the reduction in the potential for frequent T-Bone crashes that can result in extensive property damage and serious injury. There are 20 such conflicts on a traditional interchange and just two on a diverging diamond. Those two would be where the north and south lanes on Union Road crisscross.
Due to the interchange’s geometry the average speed is slowed from 40 mph to 25 mph.
To contact Dennis Wyatt, email dwyatt@mantecabulletin.com
