Why and how four horses from Webb Ranch got onto Interstate 280 on Saturday, Dec. 29, is unclear. Three of the horses were struck and killed by a car on I-280 north of Alpine Road at around 4:50 a.m., according to the California Highway Patrol.

The mature horses, trained for riding lessons, wandered from their paddock west of the freeway. There are at least two routes to the northbound lane of Interstate 280 north of Alpine Road.

Three of the horses were struck and killed by a 2006 Toyota Prius, according to an account by Tom Hubbard, Webb Ranch's corporate president. A second vehicle, a 2004 Mercedes Benz, overturned after hitting one of the horses that was down in the slow lane, according to California Highway Patrol Officer James Evans. The two drivers were taken to Stanford Hospital with minor injuries, the CHP said.

Driving the Prius was Richard Stein, 65, of Sacramento. The Mercedes was driven by Jean Gillon, 61, of Menlo Park, according to the CHP report.

The scene of the collision was about 520 feet north of the Alpine Road interchange, the CHP said. The fourth horse was found uninjured in the grass on the side of the road, he said.

Of the horses that died, two were thoroughbreds -- Maverick and Euro -- and the third was a quarter horse named Rowan, all geldings, Hubbard said. One horse was in his mid 20s and the other two in their late teens. The uninjured horse was Milo, a wild mustang repatriated from open range land, Hubbard said.

A Sig-alert, issued at 5:46 a.m., shut down northbound traffic until the alert was canceled just before 7 a.m., the CHP said.

San Mateo County animal control officials responded to the scene and the horses were towed off the road, the CHP said.

The paddock for these four horses has two gates, one of which was found with an unfastened spring-clip on the chain that locks the gate, Hubbard said. The chain may have been left unsecured by someone tending the horses, he said, but an open gate would not commonly result in the horses wandering out to the freeway. Most escaped horses are found where there's fresh grass, he said. "When they get out in the night, they go to the closest spot that they can eat grass," Hubbard said.

Horses in a group like this one can develop a herd mentality, he noted. These horses had been at the ranch for at least a year and possibly as long as five years, Hubbard said. This is the first such accident since the ranch opened in 1922, he said.

It's not unheard of for a horse to open a secured paddock, Hubbard added. "Over time, they're standing just there (watching) and they can figure out how to unlock a gate."

Horses sleep at night but don't sleep the whole night through, Hubbard said.

As to the route they took to get from the paddock to the northbound lane, that is unclear and with no tracks to go by, will probably remain so, Hubbard said. Alpine Road is the obvious route, particularly with the automatic gate not functioning. A repair service had been called but repair was not expected until after the weekend, Hubbard said.

But the ranch also has a private road that runs alongside San Francisquito Creek and under I-280. If the horses took that route, they would have come out near the fruit stand on the east side of the freeway and could have easily found the on-ramp to the northbound lane.

"We don't know how it happened," Hubbard said. "Obviously, it could have been very, very tragic," he added, alluding to the light injuries to the drivers. "So that's our concern now, is for everybody's well being."

Bay City News Service contributed to this report.

Editor's note: This is an update from a previous story.

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