Manteca is getting a third four-lane crossing of Highway 99 at the same time the first fix of the 120 Bypass/Highway 99 snafu is put in place.

But it will come with a price.

In order to make the most pressing improvements — reducing the carnage on the eastbound 120 Bypass and easing the congestion as well — with what state highway funds are available, the $131.5 million project is being built in three phases. That means the southbound off-ramp and northbound on-ramp on Highway 99 at Austin Road will be closed for at least nine years.

There a $130 billion backlog of deferred freeway and highway projects competing for gas tax revenue.

The fact that the 120 Bypass/99 interchange has secured $52.5 million for the first phase targeted to start construction in the fall of 2021 and completed by the fall of 2023 is significant.

Up until three years ago the state had no intention of upgrading the interchange until at least 2030. Manteca, led by then Mayor Steve DeBrum, put together a regional lobbying effort They cited accident rates that make it the deadliest stretch of freeway in the Northern San Joaquin. Caltrans, in the environmental study for the first phase, indicated the accident rate in the final mile of the Bypass as you approach and pass the Main Street exit is six times the state average.

Caltrans — if they had their druthers — would have eliminated all ramps at Austin Road. That’s because Austin is way too close to the 120 Bypass/Highway 99 interchange for smooth operational flows for merging traffic. The state aims for a minimum of a mile separation between interchanges. There is less than a sixth of a mile from one on ramp to an off ramp.

The existing Austin Road overcrossing built in 1955 does not have enough space beneath it for additional lanes needed to make the 120/99 interchange work as well as ease congestion on Highway 99.

David Rippende of the San Joaquin Council of Governments speaking before the Manteca Rotary Thursday at Ernie’s Rendezvous Room noted the state was only willing to fund a two-lane replacement bridge as they do not pay for growth inducing capacity.

Rippende said COG is advancing Manteca the money to allow a four-lane overcrossing with turn lanes — similar to the Lathrop Road overcrossing to be built as part of the phase using receipts from the Measure K half cent sales tax. The city will eventually reimburse COG.

The four-lane overcrossing will have the capacity to accommodate future growth in southeast Manteca. By building four travel lanes now instead of the city going back in 10 or so years is expected to save in excess of $10 million.

The replacement bridge is more expensive because it will also solve another Manteca problem. It will clear the railroad tracks — in a fashion similar to Jack Tone Road at Highway 99 in Ripon. It will reduce the number of at-grade crossing on the Union Pacific main line from nine to eight along the tracks passing through Manteca.

The first phase is designed around building a second southbound connector lane from the 120 Bypass to Highway 99.

The second phase costing $26 million addresses the northbound 99 issue primarily by adding a second transition lane to the westbound 120 Bypass. The third phase costing $53 million would restore the southbound off ramp and northbound onramps at Austin Road in such a manner that they will have minimal disruption of traffic flow on both the 120 Bypass and Highway 99.

The third phase will involve elaborate “braiding” where ramp lanes cross each other similar to the Interstate 580/680 interchange in Dublin/Pleasanton for traffic heading toward San Jose but in a much more robust manner that will allow for higher speeds and more traffic volume.

The ramp for southbound Austin would start for eastbound 120 Bypass traffic at a point near the Bypass crossing of Moffat Boulevard and the railroad tracks while  the ramp for southbound 99 traffic to access Austin would start prior to the 120 Bypass connector flyover.

Traffic from Austin Road bound for the westbound 120 Bypass would join the Bypass after passing below Highway 99 by merging with the southbound 99 to westbound 120 Bypass ramp. The Austin Road traffic heading north on 99 would join the freeway north of the Bypass/99 interchange.

Rippende said efforts are now underway to secure funding for the second phase.

To contact Dennis Wyatt, email dwyatt@mantecabulletin.com