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Will Manteca get it right?
City once again revisits 100 block of North Main
The city wants your input on how best to redo the 100 block of North Main Street when the bulbs outs are removed. - photo by HIME ROMERO/The Bulletin

The most controversial block in Manteca — the 100 block of North Main with its much maligned bulb outs — is part of three major road improvement projects the city is seeking public input on during a community meeting Wednesday.

The projects include revamping the Union Road interchange at the 120 Bypass, improving the Main Street corridor from Atherton Drive to Center Street, and improving Yosemite Avenue from Main Street to Cottage Avenue.

The meeting takes place at the Manteca Senior Center, 295 Cherry Lane, from 5 to 8 p.m. on Wednesday, Oct. 25. It will have an informal format where citizens will mingle with consultants and staff to answer questions about various options. Those attending also will be asked to submit written comments and vote on options they prefer to help the city determine the most feasible options to move forward.

The Union Road project involves a number of firsts for Manteca:

uThe Union Road overcrossing being widened to four lanes would employ a diverging diamond design that is not just a first for Manteca but California as well.

uThe city’s first separated pedestrian and bridge overcrossing over the 120 Bypass.

uAuxiliary lanes in both directions along the 120 Bypass between the Union Road ramps and those at Airport Way and Main Street to ease merging movements.

The most controversial by far among the projects involves the 100 block of North Main.

It is where bulb outs have been targeted for removal to allow for more traffic lanes. Some of the bulb outs installed in 2005 that caused the most accidents — vehicles running over the curbing — were taken out in the ensuing years.

After the council directed staff to get rid of the bulb outs in 2016 — something staff said could end up costing $1 million when all work connected with the block is completed — they came back with plans that only had two lanes in one direction and one lane in the other while maintaining the median and turn lanes.

That prompted council members in June to say before they agreed spending $1 million to redo the 100 block of North Main once again, they wants to make sure they put in place improvements that don’t have to be changed again in 5 to 10 years down the road to accommodate growth.

Councilman Gary Singh noted at a June meeting that Main Street that currently funnels down to two lanes between Alameda Street and Yosemite Avenue will likely need to be four lanes all the way from Lathrop Road to the 120 Bypass given growth projections will take Manteca for 77,000 residents today to 125,700 by 2040.

“I don’t want to have to (come back and look at it again in) 5 years or 10 years,” Singh said at the time. “Let’s do it the right way now.” 

Council colleague Richard Silverman echoed Singh’s sentiments at the June meeting. While he said he wasn’t ready to address the 200, 300 and 400 blocks of North Main Street now but he’d prefer a solution that would allow the city to take that section of North Main Street to four lanes when the time comes without having to go back and spend a significant amount of money.

Silverman advocated instead of going from one through lane in each direction to two northbound lanes and one south bound lane to consider removing the medians as well as the six remaining bulb outs. That would ultimately allow two through lanes in each direction with traffic signals set so left turn and through movements in each direction on Main Street at the Center Street and Yosemite Avenue intersections would have separate green lights allow protected left turn or through vehicle movements on the inside lane during the signal cycle. It would essentially double traffic flow capabilities in each direction.

Silverman also believes a thin, raised concrete median should go down the center of the 100 block of North Main to eliminate mid-block left turns into parking lots.

Mayor Steve DeBrum also agreed that the city needs to pursue a solution that takes the entire North Main Street corridor into consideration when it comes to traffic movement and not just the 100 block of North Main.

Several council members noted that would still allow the bike lanes city staff insists state law requires. With the medians/turn lanes left in the bicycle lanes were accommodated. Removing the median/turn lane would provide the fourth thru lane.

Such a solution would require separate green movements for northbound and southbound Main Street. In other words when northbound traffic has a green light it can turn left, right, or go straight while southbound traffic has a red light. The next step of the traffic light cycle would do the opposite.

Making that work should be fairly easy given the city is about to spend over $2 million in federal tax dollars to reprogram traffic signals citywide with the latest technology to maximize traffic flow.


Union Road


Motorists getting on and off Union Road at the 120 Bypass won’t have to worry about their turn movements being stopped by a red light if Manteca becomes the first California city to employ a diverging diamond interchange.

The project will also include Manteca’s first separated pedestrian/bicycle bridge across the 120 Bypass to address growing concerns about safety as more and more walkers head across Main Street, Union Road, and Airport Way as housing develops south of the 120 Bypass. None of the existing overpasses have sidewalks or protected bicycle lanes. The diverging diamond design as employed in other states require pedestrians and to cross into the middle of the bridge and then cross back to the edge at two signalized intersection.

Manteca opted to pursue a diverging diamond interchange for Union Road instead of upgrading the existing structure to a partial cloverleaf. 

The diverging diamond design calls for traffic lanes crossing  on either side of the bridge structure so northbound traffic would cross the bridge on the west side instead of the east side with the southbound lanes on the east side instead of the west side. Once they clear the bridge they are switched back.

The on and off ramps along with the flipping of the lanes creates two semi-diamond shaped intersections on either side of the bridge. This eliminates the need for traffic from both directions on Union Road as well as that coming from the 120 Bypass to use traffic signals to exit an off ramp or to get into an on ramp. The project will also include ramp meter signals such as now are in place on the Lathrop Road/Highway 99 interchange.

The design slashed upwards of $10 million from the $25 million estimated cost of converting Union Road into a partial cloverleaf.

The new overpass is being funded with money collected from growth as well as unspent redevelopment agency funds that were earmarked for the Union Road project.

Advantages of a diverging diamond interchange according to Advanced Transportation Solutions/America are:

uFewer conflict points (14 for diverging diamond design, 26 for conventional design).

uBetter sight distance at turns.

uTraffic calming features when desired. 

uAdditional right of way is rarely needed.

uVirtually no driver confusion based on a study and observation of existing diverging diamond design interchanges.

uConstruction time is reduced.

uWrong way entry to ramps extremely difficult.

uPedestrian crossings are shorter.

uMaintenance of traffic is simplified during construction.

There are 57 such interchanges now in place in the United States. The closest is in Reno on Interstate 580 at Moana Lane.

Caltrans is considering a diverging diamond for proposed interchange improvements in Ceres along Highway 99. The project in Ceres, though, isn’t expected to move forward until 2020. Manteca is working toward a 2018 ground breaking.


To contact Dennis Wyatt, email