Twenty-two years ago an interchange didn’t exist at Union Road and the 120 Bypass.
It wasn’t until 1997 when on and off ramps were added when the Bypass was upgraded to a full four-lane freeway status that you could access Highway 120 from Union Road.
Within 18 months, that freeway access will improve significantly.
That is when California’s first diverging diamond interchanges will be completed at that location.
The City Council on Tuesday authorized calling for bids for the $22 million project. Work is targeted to start in March with completion set for spring of 2019.
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 there 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.
Assistant Public Works Director Koosun Kim noted the diverging diamond design will allow additional lanes to be added to the overcrossing without the need to demolish the existing bridge. It also will not require additional right-of-way acquisition and has at least six month shorter construction time. Kim said that is why the Union Road interchange will cost the city $10 million less to build than a traditional interchange.
The city has $10 million set aside in Manteca RDA residual bond proceeds for the project. The city is in line for a Measure K grant using funds collected from the countywide half-cent sales tax to help cover some of the remaining fund. The balance will be “borrowed” from other major Manteca road projects.
The city has already secured a $1.4 million Measure K grant to build a separate overcrossing route for bicyclists and pedestrians to eliminate the need for them to cross the two intersections where ramps connect Union Road with the 120 Bypass.
The pedestrian bridge overpass and its approaches being built over the 120 Bypass at Union Road may be the safest place in Manteca for pedestrians and bicyclists as well as being the most homeless-proof.
The design for the pedestrian’s bridge being built as part of California’s first diverging diamond interchange is designed with a tunnel under freeway ramps on both approaches so that pedestrians and bicyclists are separated from vehicle traffic.
About the bridge for
The separate pedestrian/bicyclist route includes tunnels passing under the westbound off-ramp and the eastbound on-ramp.
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.
Once such invention is dubbed “The Mosquito”. Wales-based Moving Sound Technologies invented it several years ago and is now selling the device in North America where a number of cities, park districts, and school districts activate them after hours when facilities are closed to deter vandalism.
The Mosquito, according to the firm’s website, has a small speaker that “produces a high frequency sound much like the buzzing of the insect it’s named after.”
Anyone loitering would soon hear a sharp, high pitched noise that has been described by some in urban areas such as Washington, D.C, where they have been placed to discourage people from gathering “as giving you a huge headache” if you linger for a minute or more.
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.