No city in California has the unique "diverging diamond" road design. But if the city Ceres is able to pull off a 2020 construction start date for the Service Road interchange, motorists could for the first time in California history be finding themselves driving in a unique overpass pattern.
At Monday's Ceres City Council Study Session, City Manager Toby Wells gave an overview of what he called "what we hope to be a very exciting project for the city of Ceres."
Wells said the new interchange, which would cost an estimated $125 million, would be completely functional, calling Ceres' existing interchanges "somewhat dysfunctional in some way, shape or form."
The design is preferred with traffic volumes of 2040 in mind, 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. It also takes into consideration the railroad tracks that run parallel just to the west of 99.
"It's a pretty significant difference, all built for the ultimate capacity of this area," said Wells.
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 how motorists get off southbound 99 at Mitchell Road. Currently motorists have to stop at the end of the off-ramp and wait for clearance of southbound on-ramp traffic coming from the left. The only freeway access at Mitchell to remain would be the southbound on-ramp and the northbound freeway on-ramp.
The diamond design is better explained by 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.
Because the design produces a slower traffic movement - about 25-35 mph - there is less chance for serious accidents.
Only 17 diverging diamond interchanges exist in the nation with some in Florida, Pennsylvania, Utah and Georgia and other states. Europe has used the design for about 40 years, said Wells.
"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 old design was for couplets - where Mitchell Road was southbound and Moore Road was the northbound movement - but would not work, said Wells. It was scrapped for an expensive 2002 design plan which Caltrans ultimately rejected in 2009. The city dusted off the project in 2011 and consulted Caltrans about better designs.
Wells said the city came down to two designs. The first design - which is cheaper but not preferred - would seek to correct the way Mitchell's southbound off-ramp conflicts with the southbound on-ramp. The design, however, would do nothing to improve southbound freeway access to the west side of the 99 where the city hopes to see industrial parks built.
Wells stated his excitement, however, with the second option of the diverging diamond.
If the city gets its way, construction would start in five years and be completed in 2023. Wells said the project depends on the passage of a countywide half-cent transportation ta x 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.
Several stakeholders in developing the triangle piece bounded by Service and Mitchell roads and the freeway attended the Study Session.
"We do have folks in the area who are interested in moving forward and are in essence waiting for some concepts here," said Wells.
Because the diverging diamond design requires a bigger bite into the 17-acre chunk of land east of 99, Wells proposes the city trade its three acres recently purchased at the southwest corner of Service and Mitchell.
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.
While the design is not an absolute, Wells expects Caltrans to firm up the design approval within the next year.