Ninety-nine times out of 100, when a law enforcement officer makes a traffic stop, the encounter ends with nothing more than an exchange of documentation.

But on those rare occasions when fear of arrest outweighs rational thinking and a driver decides to attempt an escape, officers are forced into what can be a life-or-death decision-to pursue, or not to pursue.

For years, California has been the national leader in police chases, injuries and deaths.

According to California Highway Patrol statistics, there were 7,934 motor vehicle pursuits reported in the state in 2005--almost 22 per day.

Twenty-nine percent, or 2,289 of those pursuits, resulted in collisions, and 32 of those resulted in fatalities-eight of which were uninvolved third parties. An additional 374 bystanders were reported injured as a result of police pursuits.

The recent death of Margaret "Peggy" Sphar, a Simi Valley nurse left in a coma after her car collided with a local police cruiser on its way to a pursuit, once again puts the focus on a question that has been hotly discussed all the way from the water cooler to Washington: What should be police policy when it comes to vehicle pursuits?

In Simi Valley, the police department continues to operate with the mindset that allowing a suspect to escape is not usually in the best interest of the public or the cops, according to Lt. Roy Jones, head of the SVPD's traffic unit.

"It's dangerous not to continue to pursue violators, as long as the public is not put in danger by that pursuit," Jones said. "If you start letting everyone escape, then they're all going to run."

Nevertheless, Jones said, officers are expected to pay as much attention to the well-being of innocent bystanders as they do to the fleeing suspect.

"When you go into a pursuit of a vehicle, there are all sorts of things you have to evaluate. But that thought process begins and ends with public safety," the lieutenant said.

The officer's decision, Jones explained, must be made with a mental scale-on one side, all the factors that could contribute to someone outside the pursuit being injured or killed and on the other, all the circumstances surrounding the suspected violator who's being pursued. If the former outweighs the latter, then the officer is expected to put a stop to the chase.

According to the CHP, about 10 percent, or 809, of California chases were voluntarily aborted by law enforcement last year.

"If you're chasing someone who doesn't have current registration who decides to go 100 mph down L.A. Avenue, the officer using good judgment is going to leave that pursuit," Jones said. "However, if that person just robbed a bank and shot the clerk . . . then letting that person go, there's a big danger to society."

But the decision is rarely that simple.

In just seconds, a pursuing officer, with the help of dispatch and a supervising officer, must evaluate several factors, including weather conditions, road conditions, time of day, proximity to schools, potential for injury, nature of the suspect, speed of the pursuit and more.

Jones said that's why supervising officers who make the final call to pursue or not to pursue are generally some of the department's best.

"In the promotional process, we look for people who can make those kinds of reasonable decisions and can balance public safety," Jones said.

"It's a very tough selection and screening process, but that's so we can make sure we're putting people in a position of authority who've earned the right to be in that position," he said. Jones said the department will

continue to strive to keep the public's well-being in mind when it comes to chasing down the bad guys.

"We are a public entity, and as one, we are liable for any action by our employees," he said. "So we want to make 100 percent sure we are doing the right thing when we choose to enter into a pursuit."