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Pedestrian safety first
Separated path part of interchange directive
Diverging Diamond2 top
This is a four-lane version of a diverging diamond interchange that has a path for pedestrians and bicyclists in the center. - photo by Courtesy Missouri DOT

The proposed upgrade of the Union Road overcrossing of the 120 Bypass may be the first time Manteca has constructed a major traffic project where pedestrian safety is given equal footing with keeping traffic flowing.
The City Council Tuesday instructed staff to secure funding to build what could be a $1.5 million pedestrian/bicycle path  that would eliminate the need for either to have to cross off- and on-ramp traffic or pedal alongside traffic moving at 40 mph in order to cross the 120 Bypass.
It would involve building a tunnel under off and on ramps on the east side of the bridge and looping a shared two-lane bicycle/pedestrian path up to the overcrossing where a wall would separate it from the traffic lanes.  The Class I bicycle path would be American with Disabilities compliant. It also would have stairs that would allow walkers wanting — and able to do so—  to take a shortcut bypassing the loop to reach the bridge deck.
“We need to wrap our heads around the idea of spending for securing the safety of citizens,” Councilman Vince Hernandez noted in pushing the Class I design for bicyclists and pedestrians.
Hernandez noted residents south of the 120 Bypass have appeared before the council over the years expressing concern for the safety of their children either walking or bicycling across the bridges over the 120 Bypass. Hernandez added that more children are walking to school since the district changed its busing policy seven years ago.
He was joined by council members Mike Morowit and Debby Moorhead. Councilman Richard Silverman dissented. Mayor Steve DeBrum missed the meeting due to a work commitment.
Morowit noted spending a “bit more” made sense as it would eliminate pedestrians and bicyclists crossing paths with vehicles on what is excepted to be a heavily traveled interchange in the coming years as Manteca moves toward 120,000 residents.
Moorhead, who has a history of championing pedestrian safety in Manteca’s neighborhoods, noted the separated crossing for pedestrians and bicyclists “is so much safer.”
She told of how she is always worried about the safety of pedestrians and bicyclists crossing Union Road or Main Street without a barrier between them and traffic.
Public Works Director Mark Houghton said staff in discussions had noted there may be concerns with safety as part of the path’s design since it involves a “tunnel” or bridge undercrossing of roughly 60 feet under each ramp.
Staff — in order to cut costs — had proposed directing pedestrian and bicyclist into a path in the middle of six lanes of traffic protected by railing or concrete K-rail — in order to cross the 120 Bypass as part of a diverging diamond design. That would have required bicyclists and pedestrians to cross traffic four times to get across the 120 Bypass.
There are diverging diamond designs that keep the bike lane and sidewalk or separated bike path for bicyclists and pedestrians to share on both sides of the crossing. In doing so, pedestrians and bicyclists are left to cross traffic turning into and off the freeway without protection of traffic lights. If traffic lights were added it would defeat the purpose of eliminating stops for vehicles and not increase the volume that the ramps could handle.
How a diverging
diamond design works
Manteca is pursuing at using a diverging diamond interchange for Union Road instead of upgrading the existing structure to a partial cloverleaf.
Traffic lanes cross on either side of the bridge structure of a diverging diamond interchange 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 avoid needing any  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 could slash as much as $10 million from the $25 million estimated cost of converting Union Road into a partial cloverleaf.
Five different residents spoke in favor of the separated bicycle crossing. Each noted the city could commit part of the savings from going to the diverging diamond design to enhance safety of pedestrians and bicyclists for years to come.
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.
Other advantages of a diverging diamond interchange according to Advanced Transportation Solutions/American are:
Fewer conflict points (14 for diverging diamond design, 26 for conventional design).
Better sight distance at turns.
Traffic calming features when desired.
Additional right of way is rarely needed.
Virtually no driver confusion based on a study and observation of existing diverging diamond design interchanges.
Construction time is reduced.
Wrong way entry to ramps extremely difficult.
Pedestrian crossings are shorter.
Maintenance 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.