The "diverging diamond" design being proposed by the city of Ceres for the future Mitchell/Service/Highway 99 interchange is one step farther along.

District 10 Caltrans officials like the design, however, there are a myriad of other steps that must be taken.

City Manager Toby Wells said Ceres is "still in the running" to build the first "diverging diamond" freeway interchange in California. Manteca is proposing one as well, he said, but said Ceres may be farther along in the process.

"They've always been signed on but there's always steps in the process," said Wells. "One of the last major hurdles was cleared in terms of a bunch of complications of Caltrans terminology."

The next step is to complete the detailed environmental study before a preferred alternative is picked. The environmental document may be circulated for public comment by July with a preferred alternative selected and approved in early 2017.

Sacramento headquarters was concerned about the proposed interchange - centered on Service Road - would be closer than the one-mile minimum distance from the next closest interchange that Caltrans likes to see.

A second alternative on the table would be cheaper but is not desired by the city. That design would seek to correct the way Mitchell's southbound off-ramp conflicts with the southbound on-ramp but it would do nothing to improve southbound freeway access to the west side of the 99 where the city hopes to see industrial parks and more retail built.

Wells believe the proposed interchange design, which would cost an estimated $125 million, would be completely functional, calling Ceres' existing interchanges "somewhat dysfunctional in some way, shape or form."

Ceres officials like the diverging diamond design as the best to handle traffic volumes into 2040. That's why triple left-hand turn lanes are being designed for the intersection of Service and Mitchell roads. That equates to five or six times to movement potential than exists today. The design also takes into consideration the limitations caused by the railroad tracks that run parallel just to the west of 99.
Wells said the diverging diamond design would allow full freeway access at Service Road.

"You can get on and off the freeway in all directions at Service Road," said Wells.

The interchange design would also eliminate the current way motorists exit southbound 99 at Mitchell Road. The southbound off-ramp and southbound on-ramps cross each other, so drivers coming off the freeway must stop and wait for a break in southbound Mitchell Road traffic headed toward the on-ramp. Under the diverging diamond design, the only freeway access at Mitchell Road to remain would be the southbound on-ramp and the northbound freeway on-ramp.

The diamond design is explained well in several Youtube.com video. Normally a vehicle travelling westbound over a freeway overpass would be on the north side while eastbound motorists would be on the south side of the overpass. The diverging diamond flips that pattern, mostly because it allows for less traffic conflicts, better and increased traffic flows and better access to the freeway. Proper signage are a "critical component" in keeping motorists from becoming confused about movement, said Wells.

The diverging diamond is considered safer than other designs because it results in a slower traffic movement - about 25-35 mph - and affords less chance for serious accidents.

"What they found in studying them is a much less accident volumes and when you do have accidents in these type of interchanges there is a much slower velocity and so there's much less damage," said Wells.

Diverging diamond interchanges have worked successfully in Missouri, Florida, Minnesota, Wyoming, Nevada, Idaho, Texas, Utah, Kansas, Pennsylvania, Mississippi, Tennessee, Ohio, New York, Georgia and other states. Europe has used the design for about 40 years, said Wells. In all, 51 locations in the United States use the design.

The interchange design is deemed key for the development of the area along Mitchell Road near Highway 99. The Mitchell Road Shopping Center with the Walmart Supercenter has been approved north of Service Road but a triangle piece to the south can be developed once it's known where right of way is delineated.

The city has been planning a new Service/Mitchell/99 interchange since 1997. The original design called for couplets - where Mitchell Road was southbound and Moore Road was the northbound movement - but it was scrapped for an expensive 2002 design plan which Caltrans ultimately rejected in 2009. The city dusted off the interchange project in 2011 and consulted Caltrans about better designs.

If the city gets its way, construction would start in about 2020 and be completed in three years. Wells said the project depends on the passage of a countywide half-cent transportation tax in November 2016 which may fund approximately $31 million of the project. The Stanislaus Council of Governments (StanCOG) Policy Board has yet to outline how tax monies would be spent, however. The city may also use $9 million in Public Facility Fees collected on new development and would need to obtain state and federal grants. There is also the possibility of issuing bonds to finance.

In 2008 the city approved a Gateway Project for the two-parceled property with hotels and fast food restaurants but it never developed because of the recession. Developers now plan to "figure out the best land configuration for that parcel now that there's a different layout for a potential interchange," the city manager said.

In an action related to the interchange, the City Council on Dec. 14 approved the purchase of a 2.46-acre piece of property at 2807 E. Service Road for $700,000. The land is needed because both interchange designs would change access to the area.

"The roadway configurations would significantly change plus we need additional right of way for it so it was a full take," said Wells.

The Ceres City Council was introduced to the design in November 2014 and expressed excitement for it.