Manteca — if all goes to plan — will end up with eight freeway interchanges.

The city’s engineering department is working on submitting a request for Measure K funding to help get the preliminary design work done to add a fourth interchange on the Highway 99 corridor at the future extension of Roth Road.

It is roughly mid-way between the French Camp Road and Lathrop Road interchanges.

The initial work determines the scope of a possible project. It is the springboard to secure funding, eventually conducting an environmental impact study and then construction design plans.

Once the Roth Road interchange is in place, Manteca will have four interchanges on the Highway 99 corridor and four interchanges along the 120 Bypass.

It is not the only interchange project the city is actively pursuing.

On Tuesday, the engineering department shared with the City Council that work is ready to proceed on initial studies to enlarge both the Airport Way and Main Street interchanges on the 120 Bypass corridor.

The interchanges will be converted into diverging diamonds complete with separate pedestrian/bicyclist bridges just as the city did at Union Road nearly five years ago.

The design is preferred for four reasons.

*There will be no need to increase the right-of-way footprint which would mean no property would need to be acquired.

*The existing bridge deck can be incorporated into the diverging diamond design.

*The reduction in turn movements reduces the potential for T-bone crashes and improves traffic flow.

*It takes less time to construct and there is less traffic disruption during construction.

*It costs less than cloverleaf and other interchange designs.

The Union Road interchange was California’s first diverging diamond. 

The 120 Bypass will also see another first as the two interchange upgrades are put in place — California’s first location with two consecutive diverging diamonds and then three consecutive diverging diamonds.

Each interchange has a $35 million price tag so it is highly unlikely both will be built concurrently.

It has not been determined if the Roth Road will be a diverging diamond as well.

But it could be if the Manteca City Council uses the same line of reasoning that their counterparts did in Tracy last July in authorizing spending $42.8 million for the state’s second diverging diamond interchange on Interstate 580 for the development of 1,700 acres.

Tracy wanted to be able to have safer and smoother movements not just of vehicles but also of a significant amount of truck traffic going to and from business parks.

The Roth Road extension from Airport Way to Highway 99 is envisioned as a truck route to allow the development of business parks to the north of its alignment as well as handle growing truck traffic from Union Pacific Railroad’s intermodal facility and existing business parks that are partially developed.

The interchange would also likely open up northeast Manteca to development.

It was noted Tuesday that Manteca last year completed the adding of ramps and associated surface street widening to convert the 120 Bypass’ McKinley Avenue overcrossing into an interchange.

Work also has started this year on the replacement of the Austin Road interchange on Highway 99.

Manteca is paying for the replacement interchange being built in connection with the 99/120 upgrade project to carry four through lanes instead of two.

To contact Dennis Wyatt, email dwyatt@mantecabulletin.com