DIABLO — In the bucolic, country club community of Diablo, a growing menace is threatening residents: “loud packs” of bicyclists “careening” through the streets, overtaking cars, endangering small children and wreaking havoc on the pristine quietude of the tiny, East Bay enclave.

Now, some residents, who’ve been fighting the influx of cyclists for several years, are taking their battle to court. They’re seeking a judge’s order to declare Diablo’s western entrance, Calle Arroyo, private — a move that would allow the community’s governing board to limit recreational use and cite trespassers in the latest Bay Area battle pitting private property rights against public access.

For at least a decade — and by multiple accounts, a half century or more — cyclists, along with parents pushing strollers and neighbors walking dogs, have turned down the quiet, unlined street to escape the fast-moving traffic of Diablo Road in Danville. Some continue past the country club parking lot, before veering onto an unmarked dirt trail to reach Mount Diablo State Park, its multiple biking and hiking trails, campgrounds and expansive vistas.

For resident Robert Tiernan, the lead plaintiff in the lawsuit, the issue is one of safety and the expectation of privacy in a community closed to the public.

“Our roads were never designed to become a bypass for Diablo Road,” Tiernan said. “We want to return our roads back to a safe place, where all residents can enjoy it and have their peace and privacy.”

But bicyclists contend that without the cut-through, the public would be denied a safe access point to a state park — on roads that are maintained with public money — and would be forced instead to traverse the windy, narrow corridor of Diablo Road, which has no shoulders, sidewalks or bike path.

To the cyclists, and some residents in Diablo, that’s tantamount to a death sentence.

“It’s dangerous,” said cyclist Rip Talavera, who has been cutting through Diablo for the past 35 years to climb Mount Diablo’s world-class mountain biking trails. “You’d get killed on Diablo Road. You have no choice but to go through there.”

The lawsuit is only the latest attempt to block cyclists from using the country club community’s roads. Complaints from residents prompted the community’s governing board in 2013 to propose refusing entry to anyone who is not a country club member, resident or guest. But, Tiernan said nothing came of that effort.

Richard Breitwieser, the general manager of the Diablo Community Services District, declined several requests for an interview. But, in a 2015 memo he wrote to Diablo’s governing board, Breitwieser admitted it would be a stretch to block the public from using Diablo’s roads and cited two past legal opinions, dating as far back as 1972, that reached the same conclusion.

“Both (previous legal opinions) agree that the public has obtained a right of way over Diablo Roads,” he wrote. “In fact, it is probable that the public has used Diablo roads as a pass-through road for more than 50 years.”

Diablo also receives county tax money to maintain the roads, said Bob Campbell, the auditor-controller for Contra Costa County. Last year, that amounted to $663,871, he said. This year, it’s expected to be $683,000. Campbell was explicit in his definition of those monies: “They are public funds.”

“They only get those dollars because those roads are designated for public use,” said Steve Whalen of the Valley Spokesmen Bicycle Club, adding that when people use public money for private benefit, “That’s called corruption.”

Plus, the alternative — cycling up Diablo Road — is far more dangerous, he said. There were 146 collisions on Diablo Road between 2007 and 2017, including one in October that seriously injured two cyclists, according to the California Highway Patrol. During the same period, there were 31 collisions in the community of Diablo. None were reported on Calle Arroyo, though Tiernan said he and his family members have been involved in at least four run-ins on the street.

There is a plan to build a bicycle and pedestrian trail parallel to Diablo Road as part of a proposed 69-home development across from Diablo, said Robert Ewing, the town’s attorney. But that development is caught up in litigation — ironically, over concerns that increased traffic would endanger cyclists.

In the meantime, many Diablo residents have welcomed bicyclists and other recreational users.

Omid Bahrami, whose Diablo property includes the short pathway connecting Alameda Diablo to Mt. Diablo Scenic Boulevard, trims vegetation to provide better visibility to cyclists for oncoming traffic. He even allowed a bicycling group to upgrade the dirt path to a compact surface so it doesn’t get muddy when it rains. If there’s a problem with cyclists speeding by, Bahrami said the district should work with them to find a solution, not shut them out.

“We have such a nice neighborhood, and naturally (the cyclists) didn’t take away from the neighborhood, they added more diversity by bringing nice people to the area and introducing Diablo Country Club to so many new guests,” he said.

The neighboring Athenian School and nearby San Ramon Valley and Monte Vista high schools use the cut-through for their cross country and mountain biking teams so they can avoid Diablo Road. The coaches emphasize good behavior through Diablo, telling team members to ride single file and not to talk while riding through there, said Gabriella Dube, 16, who has been on San Ramon Valley High School team for the past four and a half years.

“But we’re a group of teenagers,” she acknowledged, “so that doesn’t always happen.”

Resident Robert Canepa sees growing bicycle traffic as a real threat to safety. Recreational users can choose to go elsewhere. He has no other option to get to his house.

“We just don’t want anyone to get hurt on the street,” he said. “The more people who come down here, the greater the opportunity is.”

For cyclist Andy Stein, a Danville resident who said he’s been cutting through Diablo for 25 years, the issue is exclusion. He drew parallels to the controversy surrounding Martins Beach, a Half Moon Bay surfing destination that was closed to the public after tech billionaire Vinod Khosla bought the surrounding property. The ongoing legal saga is now being appealed to the U.S. Supreme Court.

“Diablo is a private country club (community), and I hate to say it,” he said, “but wherever rich people are, they want to restrict things.”