Roadshow: Full cloverleaf interchanges are a thing of the past


Contra Costa Times
Interstate 580-680 interchange in Dublin, Calif.

Q Why have some of the cloverleaf exits been removed at the Capitol Expressway and Tully Road connections with Highway 101? Traffic backs up in all directions at these connections and is horrendous. Cloverleafs would eliminate the need for some traffic lights, thereby enhancing the flow of traffic.

Harvey Wolfe

San Jose

A A bunch of engineers disagree. Caltrans has been designing partial-cloverleaf offramps for more than a decade. This is where at least two ramps come off the freeway at a diagonal and exiting cars may face a stoplight before turning onto a side street. Cloverleafs allow cars to move freely without stopping as they loop around the exit, but that happens only when traffic is light. When traffic increases, the short weaving space between the loop ramps causes a terrible merging mess.

A 1999 study by the Virginia Department of Transportation found that cloverleaf interchanges begin to bog down when traffic surpasses 1,000 vehicles per hour. At Capitol and 101, the number is higher and will increase.

The preferred alternative is the partial-cloverleaf design. The Virginia study also concluded that cloverleaf interchanges have the most fixed-object accidents, such as slamming into concrete barriers, of any type of interchange. Those usually happen when motorists are forced off the road in the battle to merge with other drivers.

One of my closest crash encounters occurred at the 17-880-Stevens Creek interchange when a driver blew down a cloverleaf ramp and nearly sideswiped me. He never slowed down or even looked in my direction.

The fact that he was on a cellphone didn’t help.

Q The median on Capitol Expressway in San Jose between Tully and Story roads is overgrowing with weeds. I’ve called the city, which tells me it’s the county’s responsibility. County sends me back to city and to Caltrans and everyone says it is not their job. Why spend so much money to fix the median and let the weeds grow all over?

Janice Montalvo

San Jose

A The county says after some confusion that this is its responsibility. Because removing weeds often requires hands-on work and not just spraying with chemicals, crews can easily fall behind this time of year. Look for weed trimming in a few weeks.

Q Is there a reason there is no signal controlling cars coming off northbound Highway 17 at White Oaks Road in Campbell? Cars fly off the highway without letting someone through, and then when traffic finally backs up because of the light at Camden, they all pull forward, effectively blocking access for those at the stop sign waiting their turn, which only comes after waiting 10 minutes at a time.

Jesse Lara

A The idea of signalizing this offramp has been considered a number of times over the past few decades but several concerns have stymied those efforts. One is the potential to back up traffic onto 17 and to increase cut-through traffic on White Oaks and other neighborhood streets.

Traffic planners once discussed eliminating the northbound ramp to 17, requiring White Oaks drivers to use the Camden onramp. But nearby residents did not like that idea.

Look for Gary Richards at Facebook.com/mr.roadshow, follow him at Twitter.com/mrroadshow or contact him at mrroadshow@mercurynews.com or 408-920-5335.