By HOWARD FINE

Staff Reporter

Commuters beware.

In just three months, crews will be putting up those familiar concrete barriers on the southbound San Diego (405) Freeway and begin building an eight-mile carpool lane through the traffic-clogged Sepulveda Pass.

The two-year, $18 million project is the first step in a 10-year plan to close a 19-mile carpool-lane gap along the 405 from the Ventura (101) Freeway to the Century (105) Freeway, just south of Los Angeles International Airport.

Much of the project remains in the preliminary stages. But if it should go ahead, the total cost could hit $300 million.

Few would argue that the 405 is one of the most congested freeways in the L.A. Basin. But questions remain about whether the expensive carpool lanes can actually unclog the daily jams.

"This project is desperately needed," said L.A. City Councilwoman Ruth Galanter, whose district includes much of the freeway south of Santa Monica Boulevard. "On the south end, you've got all the people going to the airport. But long before you ever approach the airport, you have huge sets of workplaces on the Westside that people use the freeway to get to."

Critics, however, cite studies showing that the overall percentage of Southern Californians riding in carpools has remained constant at about 15 percent over the past decade, despite the addition of hundreds of miles of carpool lanes.

"The fact that they are planning to add an additional lane to the 405 is very good news because more capacity is so desperately needed," said Assemblyman Tom McClintock, R-Granada Hills, a fierce opponent of carpool lanes. "The bad news is that this new lane will be closed to 93 percent of the cars, who will see little or no relief from the congestion they face every day."

McClintock is pushing legislation to ban construction of new carpool lanes and turn existing ones into general-use lanes. His legislation has been killed this year but could re-emerge in 2000.

McClintock and other opponents point to the experience of New Jersey, which recently moved to open carpool lanes to all traffic.

"The gridlock that had plagued the areas disappeared overnight," he said. "The one nice thing about the plans for all this construction is that the concrete will not go away. At a later date, with a little common sense and sandblasting, these carpool lanes can be turned into mixed-flow lanes."

Caltrans officials disagree.

"Our view is that carpool lanes can move two to three times the number of people as a general mixed-flow lane," said John Robin Witt, a spokesman for the agency. "It is one of the ways that we make our freeways and highways more efficient so that we can accommodate the tremendous growth that is taking place."

In any case, it will be a long wait for drivers eager for the day when they can travel in a continuous carpool lane from the San Fernando Valley to Orange County. State transportation officials say it will take at least 10 years to finish the job, which will start this August.

The reason? On much of the 405 through the Westside, there is no more existing freeway space to add a carpool lane. So the roadway will have to be widened, at a cost of $15 million to $20 million per mile. (Caltrans has yet to determine just how many miles of widening would have to take place.)

"When it comes to adding carpool lanes on the 405, we've done most of the easy stuff," said Alberto Angelini, supervising transportation engineer for the District 7 office of Caltrans. "The ones we're starting to get into now are more complicated because lanes can't simply be added. The freeway has to be widened, which costs more money and takes more time."

While it might cost less to simply designate an existing lane for carpoolers, Caltrans has a policy against that practice, Angelini said. The policy was put in place almost 20 years ago in response to the uproar that followed the conversion of an existing lane into a "Diamond Lane" on the Santa Monica (10) Freeway.

And freeway widening along the 405 would be no simple task, according to Caltrans planner Melvin Hodges. More concrete has to be poured, more bridges expanded and more pilings sunk into the bedrock. And, in some areas, more land might have to be acquired.

Thus far, only the southbound carpool lane through the Sepulveda Pass has been funded, though several other segments are in line to receive state and local funds over the next five years. Some segments, like the northbound 405 through the Sepulveda Pass, have yet to be planned and remain years away.

Indeed, Hodges said that stretch is shaping up to be the costliest segment of all because of the immense amount of freeway widening it will require. He put the cost at between $100 million and $200 million.

In the short run, though, commuters are likely to face another problem: traffic bottlenecks around the points where the carpool lanes end.

The first is expected when the southbound lane to be built starting in August is finished in mid-2001. It will end abruptly about a half-mile south of Sunset Boulevard, dumping cars into existing lanes of traffic. It will take at least another four years before the next segment to the Santa Monica Freeway is completed, which in turn is likely to exacerbate the already critical congestion at that busy interchange.

"What we're going to have here is carpool lanes coming into the most congested region and then they will disappear," Galanter said. "You will be compressing the traffic down to the existing lanes, which worries me greatly."

Already, residents in the Brentwood Glen neighborhood west of the 405 and south of Sunset are wary and not just because of potential bottlenecks. They say traffic often backs up onto the freeway from off-ramps at Sunset and Wilshire boulevards.

"When the off-ramp traffic backs up onto the freeway, it creates a very dangerous situation," said Scott MacGillivray, a Brentwood Glen resident. "You've got one lane of the freeway at a complete stop while in the other lanes, cars zoom by at 60 mph. You throw in a carpool lane and it makes the situation even more complicated."

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