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Caltrans considering Ceres diverging diamond idea
Driving a diverging diamond interchange may be confusing at first but is quite simple. The design relies heavily on good signage to direct drivers. Ceres wants this design for the Service/Mitchell/99 interchange. Caltrans is studying the concept. - photo by Contributed to the Courier

Although the design is being used successfully in a number of states, Caltrans is acting slowly to approve the "diverging diamond" design for the future Mitchell/Service/99 interchange.

Caltrans officials from District 10, which covers Ceres, like the design but it is being viewed cautiously at state headquarters.

For one thing, Caltrans has never approved the unique "diverging diamond" road design. For another thing, the proposed interchange - centered on Service Road - would be closer than the one-mile minimum distance from the next closest interchange that Caltrans prefers. If Caltrans has misgivings about the distance to the downtown interchange, Ceres may have to go with a less desired alternative.

City Manager Toby Wells said Caltrans routinely moves very slowly in all aspects of business but particularly when new concepts are proposed. Other diverging diamond designs are before Caltrans, he said, but Ceres has a project which is closer to development time. He expressed hopes that the state will adopt the design but is bracing to go with the second and cheaper alternative. 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 built.

"Caltrans has not yet approved a diverging diamond design anywhere in the state and has concerns even though many other states are using this concept with great success," said Director of Engineering/ Daryl Jordan.

If Caltrans decides to try the design, Ceres could be the first city in California to use it, especially if the project starts in 2020.

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

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 design, believing it's the best to handle traffic volumes into 2040, said Wells. 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.

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.

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 get off southbound 99 at Mitchell Road. Motorists now must stop at the end of the off-ramp and wait for clearance of southbound Mitchell Road on-ramp traffic coming from the left. 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 better explained in a Youtube video, which Wells showed to the council. Typically 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, 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.

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.

"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."

The city has been planning a new Service/Mitchell/99 interchange since 1997. The original design was for couplets - where Mitchell Road was southbound and Moore Road was the northbound movement - but later proved to be unworkable, said Wells. 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 five years and be completed in 2023. Wells said the project depends on the passage of a countywide half-cent transportation tax in 2016 which would fund approximately $31 million of the project. The city also can 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.

Wells expects Caltrans to firm up the design approval within the next year.

To see videos of the diverging diamond, visit or