Not only is the Union Road/120 Bypass interchange widening project starting this spring designed to ease future traffic congestion, reduce the chances of collisions and cost less to build but it will be constructed in less time.
Bids for the converging diamond interchange — the first ever to be built in California — are due in early February. Public Works Director Mark Houghton has noted if the project stays on schedule it will be completed by the end of the year. If the widening from two to four lanes was done as a traditional interchange it would take between 18 and 24 months to complete.
The project will also include the city’s first dedicated overcrossing of the 120 Bypass for bicyclists and pedestrians.
Caltrans District 10 helped clear the way for the design that has been deployed in 80 plus other locations in the country — with the nearest being on Mona Lane in Reno.
The flow across the freeway has lanes crossing 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.
The design for the pedestrian bridge has tunnels under freeway ramps on both approaches so that pedestrians and bicyclists are separated from vehicle traffic.
Designers noted that such tunnels in other communities often have become places for the homeless to camp. The design team was worried about the safety of pedestrians after dark from criminal elements.
As a result the tunnels will have:
Security cameras placed and protected so they can’t be damaged to provide live feeds backs to the Manteca Police Dispatch Center.
There will be extensive lighting that will also be placed and protected in a manner where they can’t be damaged.
There will be a 24-hour emergency button tied in directly to the 9-1-1 system.
It will be equipped with a device that emits continuous noise that is extremely uncomfortable to hear for an extended period of time.
The city is seeking to avoid safety being compromised by homeless and others potentially camping in the tunnels. Noting that illegal encampments have been in place along freeways where decibel levels are high, staff has said the city is looking at several devices that emit high frequency noises.
The pedestrian bridge will be built on the east side of the existing overpass and will be 12 feet wide.
Pedestrians and others will drop down from street level at a grade that meets Americans with Disabilities Act standards, use a tunnel to go under the freeway ramps and then climb upward on a circular path to the bridge where they are protected from traffic with a barrier and then repeat the process in reverse on the other side.
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