As Summertime Fades, So Does the Easy Commute : Traffic: With students and workers returning from vacations, heavier traffic again clogs the freeways.

It might seem a commuting contradiction, but Sandi James practically savors driving to work during the lazy, hazy days of summer.

Sure, there are still plenty of cars clogging freeways between her home in Monrovia and her job in downtown Los Angeles. And the occasional jackknifed truck can just as easily cause a rush-hour rumba line. But overall, she says, traffic simply seems to flow better in the summertime.

Unfortunately, that blessed respite from the gridlock is about to end. With kindergartners and college students alike heading back to school, and workers returning from late-summer vacations, commuters once again will be slamming on the brakes across the Southland beginning today.

“I just dread it,” said James, a legal secretary and seasoned commuter. “Right after Labor Day, the freeway once again becomes hell. Driving hell. I just don’t like to think about it because I’d be looking for a new job--or a new city.”

It is the goodby-summer-hello-September surge. Traffic experts and commuters say it’s as punctual as a groundhog, as reliable as the swallows’ annual return to Capistrano. The first weeks of September, they say, mark the traditional debut of the worst commuter congestion on freeways in Los Angeles and other metropolitan areas up and down the state, as society gears up again after a hiatus under the hot summer sun.

“I think it’s generally recognized that commuter traffic tends to flow better during summer,” said Nick Jones, a transportation engineer with the California Department of Transportation. “The week after Labor Day we’ll all be out banging our heads in it again. More than anything else, it’s people back from vacation. Everyone is just getting into the grind again.”

It’s just one of several traffic seasons on the state’s network of freeways, which ebb and flow in a pattern that experts can forecast like changes in the weather.

“There’s several big trends,” said Keith Gilbert, highway engineering manager for the Automobile Club of Southern California. “During Christmas vacation, some of the aerospace plants are closed and schools are out, so this makes a difference in the commute hour, although it gets tight around the shopping centers. Traffic also tends to lighten during Easter Week.”

Nothing, however, is quite like the jolt that follows the Labor Day weekend.

Take a look at rush hour on the San Bernardino Freeway. On a morning commute in mid-September last year, traffic was moving 25% slower than it had just one month earlier. Caltrans says that’s because 12% more cars were on the road in September.

There are other signs that summer is the best time to commute. One day last spring, commuters on the San Bernardino Freeway in Alhambra didn’t exceed 20 m.p.h. until 10:30 a.m. But on a July day, the commuter parade had accelerated to 40 m.p.h. or better by 9 a.m. In the transportation-speak of Caltrans, that’s free-flow.

Experts say several factors blend to produce the smoother commutes of summer and the mind-boggling jams of September.

For starters, there are the crowds of students that descend on commuter campuses such as Cal State Fullerton, UCLA and Cal State Los Angeles for fall semester. At Cal State Northridge, for instance, only about 4,000 students and faculty drive to campus during the summer session, but that number quadruples to more than 16,000 when the regular school year starts today.

Elementary schools and high schools also have an impact, transportation planners say. School buses and moms toting kids to grade school add to September’s traffic mix, as do high school students who roar into the gridlock lacing suburban communities.

While the elements seem to be on the side of the commuter during the summertime, that advantage vanishes as fall approaches. It gets dark earlier and, soon enough, drops of rain will muss the delicate driving sensibilities of Angelenos. With the change from daylight-saving time on the last Sunday in October, the freeways get downright ugly, grizzled commuters say.

“The first day it gets dark (earlier) it’s like a kiss of death,” said Tim Skrove, who has racked up more than 200,000 miles in seven years commuting 60 miles each way between his home in Riverside and job with the Metropolitan Water District in Los Angeles. “I don’t know if it’s that people have lost track of driving in the dark or what, but it just causes havoc for commuters for a substantial period of time.”

But the most significant factor, experts say, is simply the marked reduction of rank-and-file commuters during the summer, as workers take advantage of sultry weather to pack up the kids and leap into a few weeks of vacation. Even a small drop in the horde of cars parading up on-ramps can transform a freeway into a model of transportation efficiency a Southland motorist would die for.

“I think we are talking about a 10% absence due to vacations for many weeks during the summer,” Gilbert of the Auto Club said. “Even a 5% drop in the number of cars can mean a difference between 25 m.p.h. and 55 m.p.h.”

Indeed, Southern California’s freeways flow with the same symphony of motion as logs down a crowded river. While a roaring tributary can handle lots of logs, a few too many will cause a horrendous bottleneck. So it goes with a freeway. Add just a few too many cars and a highway that was operating efficiently is reduced to a crawling mass of disgruntled motorists.

Ken Bauer, who rides a van pool each morning for the 42-mile trip from his Westlake Village home near Ventura County to downtown Los Angeles, estimates that he saves anywhere from 10 to 20 minutes on each leg of his commute during the summer. Bauer said the congestion actually seems to grow through September, building up “a full head of steam” by month’s end.

David Stein, a transportation planner for the Southern California Assn. of Governments, can even measure the differences on his short commute from South Pasadena to Los Angeles. During the school year, he hits a solid wall of traffic on the Pasadena Freeway anywhere from two to six miles from downtown. During summer, the queue of cars is only about a half-mile long, he said.

“It’s a very big difference,” Stein said. “The problem with traffic is that congestion begins to increase sharply as you add just a few more cars. You literally get to the point where that one extra car is the straw that breaks the camel’s back and causes congestion.”

There’s more than a touch of irony to the glowing reviews of Southern California freeways in the summer.

Because of the traditional flood of out-of-state visitors, California’s highways actually handle more traffic during August than any other month of the year. Fortunately, all those cars are spread more evenly through the day. Tourists tend to steer clear of the freeways during peak commuting hours.

As a result, rush-hour speeds are better, but traffic during other times of the day can actually be heavier as tourists and vacationing locals hit the pavement, transportation experts say.

“The commute hours are slightly better in summer, but that’s about it. The rest of the day is packed,” said Jill Angel, a California Highway Patrol sergeant who doubles as on-air anchor for KNX-radio’s afternoon traffic reports. “It all just depends what area you’re talking about. The beach areas and the airport are always bad. The 5 through Anaheim is bad because of Disneyland and 101 through Hollywood because of all the attractions there.”

And a seemingly insignificant event like a stalled pickup or a minor fender-bender can cause the speediest summer commute to screech to a halt.

“There’s terrible days even in the summertime where you’ll have accidents or those freak episodes when everyone just wants to drive slow and there is congestion for no apparent reason,” noted Skrove, who shifted his working hours so he can leave at 5:30 a.m. to make his 90-minute commute. “My attitude is that the drive is just part of the day. I’ve just reconciled myself to an 11- or 12-hour day.”