A flurry of behind-the-scenes negotiations between Caltrans, PG&E and the City of Manteca has saved the diverging diamond interchange project at Union Road and the 120 Bypass.
The solution, though, will cost Manteca $1.8 million.
The issue was over who would be paying for the cost of relocating four PG&E high-power transmission poles needed for the project to proceed. Typically the state and utility providers — in this case PG&E — split the cost 50-50 when power lines need to be relocated for a highway or freeway project based on a master agreement. The paperwork, however, specifically for the Union Road line could not be located.
Without documentation PG&E refused to pay anything for the moving of the power poles. Caltrans, leery of setting a costly precedent, declined to pay for more than 50 percent nor did they favor the city picking up PG&E’s share. At one point when the city proposed picking up the entire tab Caltrans — still concerned about statewide implications — withheld blessing such a move and indicated if Manteca proceeded they may be forced to withhold future highway funding from projects involving Manteca.
Between efforts of City Manager Tim Ogden, Public Works Director Mark Houghton, and Deputy Public Works Director Koosun Kim that hurdle was cleared to the satisfaction of Caltrans and PG&E allowing it not to be viewed as a precedent.
Meanwhile the contract the City Council approved with Teichert Construction in March for $23.7 million to build the project — the first diverging diamond interchange in California — had not been signed by Ogden in order not to commit the city to paying Teichert a portion of the contract if the project was not able to move forward.
Houghton on Tuesday told the council Teichert was still willing to honor the low bid.
The city is now in the process of trying to identify where the additional $1.8 million will come from. The San Joaquin Council of Governments is working on that aspect as well and is scheduled to consider possible assistance at a meeting on Thursday.
Why the diverging
diamond design was
selected by Manteca
The diverging diamond approach was recommended by Public Works Department staff after they were tasked by elected leaders to try and come up with the most cost effective upgrade for the interchange.
The only other requirement was to move larger volumes of traffic.
Originally the plans called for a half cloverleaf that would have required taking nearby property including several homes.
Staff looked into diverging diamond designs that were deployed in other states that were selected not for cost savings as much as it was to place interchanges that worked effectively in developed areas without taking more land and to improve safety.
In the case of Manteca the design means a project price tag that was $10 million less as no additional land was needed. Also a cloverleaf style interchange would have required demolition work resulting in a longer construction frame.
As an added bonus the design allows for faster and smoother traffic flow and — based on observations of diverging diamond interchanges in place — less severe collisions as well as fewer accidents.
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
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.
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