Just when you need a cop, he's out with his wife or driving a semitrailer-truck.

An off-duty Salt Lake County deputy sheriff took his wife and another couple on a wild ride Saturday as he joined Summit County deputies and the Utah Highway Patrol in a high-speed chase from Salt Lake City to Coalville.A California woman had been driving erratically when the off-duty officer attempted to pull her car over, a Salt Lake County sheriff's report said.

The chase began at 2:39 p.m. near Lamb's Canyon on I-80 when the officer attempted to pull over Sue Ann Emerson, 23, said sheriff's Lt. Chuck Christensen.

Emerson made a U-turn near Wanship, Summit County, officials said, with the off-duty officer, Summit County deputy sheriffs and Utah Highway Patrol troopers following. Speeds during the chase exceeded 100 mph.

An off-duty UHP trooper who was driving a semitrailer-truck westbound on I-80 and another patrolman in a marked unit slowed down to about 15 mph, Christensen said, to let traffic back up while Emerson and the officers caught up.

The woman came up on the impromptu traffic jam with three lanes blocked, and went off the right side of the freeway. She was not injured, and Christensen said, "In fact there was no accident involved."

Emerson was booked into Salt Lake County Jail for investigation of driving under the influence, fleeing a police officer, reckless driving, imperiling the lives of others and speeding, Christensen said.