Your odds of getting in a collision on the 120 Bypass as you near Highway 99 if you are trying to head south toward Ripon and Modesto is six times higher than the statewide average.

Caltrans indicated that high traffic volume during the afternoon commute that sees in excess of 2,000 vehicles an hour trying to go from the eastbound 120 Bypass to southbound Highway 99 creates a backup for at least a half mile for a number of hours. The state notes that motorists — impatient about the delay — will use the fast lane or inside lane to travel as far as they can to the split and then cutback into the much slower moving traffic in the right lane. That leads to rear-end collisions and an accident rate six times higher than the average for a California freeway.

It is just one tidbit of data included in Caltrans’ proposed mitigated negative impact report for a three phased, $131.5 million project designed to reduce the carnage and congestion at the 120 Bypass and Highway 99 interchange. There was an accident every 15 hours at the interchange and freeway approaches in 2018 that required Manteca Fire Department units to respond.

As it stands now Caltrans has identified the $52.5 million funding for the first phase of the project. The goal is to award the contract in the summer of 2021, start construction in the fall of 2021, and have work on the first phase completed by the fall of 2023.

The first phase involves:

uwidening the eastbound 120 Bypass to southbound 120 Bypass connector from one to two lanes.

uremoving the Austin Road overcrossing and replacing it with a longer span that ultimately would allow eight freeway lanes plus auxiliary lanes on Highway 99. The replacement bridge would span the Union Pacific Railroad tracks as well eliminating the at-grade crossing on Austin Road.

uadding a new connector road from Austin Road to East Woodward Avenue. The existing railroad crossing on East Woodard Avenue would be modified to conform with the new connector road and provide access to Moffat Boulevard.

umodifying the existing northbound Austin Road exit ramp to conform with the higher overcrossing profile of the replacement bridge.

uclosing the northbound onramp and the southbound off-ramp for Highway 99 at Austin Road. The length of the closure is currently estimated at 9 years. Reopening of the replacement ramps will depend on the availability of funding for the third phase.

The second phase costing $26 million would:

uwiden the connector from northbound Highway 99 to the westbound 120 Bypass from one to two lanes.

uconvert the existing structure crossing Highway 99 to the 120 Bypass to two lanes.

uconstruct a new separation structure to serve eastbound 120 Bypass traffic to the northbound Highway 99 connector ramp.

uadd a westbound auxiliary lane on the 120 Bypass from the Highway 99 interchange to Main Street.

uadd an eastbound auxiliary lane on the 120 Bypass between Main Street and Highway 99.

The third phase costing $53 million would:

urestore the southbound off ramp by constructing a grade-separated braided ramp to eliminate weaving with 120 Bypass merging traffic.

uconstruct the entrance ramp from Austin Road to northbound Highway 99 and to the westbound 120 Bypass as a loop ramp that will separate traffic movements to Highway 99 and the 120 Bypass.

urelocate the northbound Highway 99 exit ramp to Austin Road to accommodate the loop onramp.

urelocate the Highway 99 frontage road for about 0.8 miles.

uadd an auxiliary lane in each direction on Highway 99 from the 120 Bypass to about 1.7 miles south of Austin Road by shifting the median away from the Union Pacific right-of-way and relocating the frontage road.

uadd an auxiliary lane in the existing median of the eastbound 120 Bypass from Main Street to Highway 99 to provide a dedicated lane to connect to the new 120/99 separation structure.

The high cost of the third phase design is reflected in it being necessary not to impede traffic flow and create a major safety hazard from the 120 Bypass south to 99 and from 99 going north to the eastbound 120 Bypass.

In order to do so 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.

Caltrans estimated the second and third phases could start construction in March 2030 and be completed by September 2031. Since it is highly dependent on funding, it is possible there could be a nine year gap between the two phases.

The Caltrans document reflects the fact there is no longer any project on the 20 to 30 year planning horizon to extend the Bypass east of Highway 99. That means East Highway 120 will remain as the route of travel.

Copies of the Caltrans document are available at the Manteca Library, 320 W. Center St., Manteca City Clerk’s office, 1001 W. Center St., or online at the Caltrans District 10 website.

Comments on the project are being accepted through May 25.

To contact Dennis Wyatt, email dwyatt@mantecabulletin.com