SAN MARCOS -- In the ongoing battle over whether a Wal-Mart should be built in south San Marcos, one of the key points of contention has been just how much traffic the store will bring to roads already clogged with cars.

Critics have said the store will take gridlock on Rancho Santa Fe Road to a new level and are fond of showing pictures of other Wal-Marts with full parking lots and a line of waiting cars.

Supporters have seized on the city's traffic studies that predict a plan to allow Wal-Mart in the University Commons development will actually put fewer cars onto Rancho Santa Fe Road.

"They're saying Wal-Mart will be about 4,400 trips a day. The reality is there will be 10,000 cars a day," said Paul Stailey, a Carlsbad resident who lives near the Wal-Mart site. Stailey is a member of saveSanMarcos.org, which is campaigning against Wal-Mart.

The City Council in August approved the store at Rancho Santa Fe Road and Melrose Drive. Opponents quickly gathered enough signatures to force a referendum on the matter. The resulting Proposition G will be on the March 2 ballot.

Since plans for the store first surfaced last year, traffic has been one of the chief concerns residents have voiced. But the city's studies haven't born out those concerns.

The city's environmental study on University Commons found that the overall impact of the new plan, which includes rezoning 20 acres from residential to commercial to allow Wal-Mart and other changes, will be a decrease of 12 average daily car trips on area roads. During the morning and afternoon rush hour there will be a decrease of about 80 trips, according to city documents. The entire project is expected to generate 15,255 average daily trips.

On the average weekday, there are 31,000 trips made along Rancho Santa Fe Road between Lake San Marcos Drive and La Costa Meadows Drive, according to the city's most recent traffic count. The city is widening Rancho Santa Fe Road from two to four lanes between Melrose and Island drives to accommodate growth in south San Marcos. The project should be finished by this summer.

"The traffic on that road isn't going to be caused by Wal-Mart," said San Marcos Development Services Director Charlie Schaffer, referring to Rancho Santa Fe Road.

"It's going to be caused by normal growth in the area," he added, noting that communities like San Elijo Hills and University Commons in San Marcos and the Villages of La Costa and Bressi Ranch in Carlsbad will add thousands of homes to the area over the next several years.

Carlsbad is widening its portion of Rancho Santa Fe Road to six lanes and some San Marcos residents have said their city should be doing the same, contending that Carlsbad is better accommodating its growth.

Schaffer said traffic studies have shown that four lanes will be adequate.

"It gets down to money. There are very few public agencies that build more than they need," he said. Acquiring the needed right of way would have been costly and time consuming and widening the road to six lanes would be more of a burden to area residents, he said.

At four lanes and with additional traffic signals, Rancho Santa Fe Road will be able to handle the added traffic from Wal-Mart, Schaffer said.

There will be a traffic signal at Rancho Santa Fe Road and Melrose Drive, which is being extended. There will also be traffic lights at both ends of a loop road called Boulder Ridge Road, one where it meets Melrose Drive and one where it meets Rancho Santa Fe Road, that goes by the store, Schaffer said.

And there will be traffic signals along Rancho Santa Fe Road at Redwing Drive and Meadowlark Ranch Road, the entrances to Meadowlark Ranch Community. Meadowlark Ranch is an unincorporated community off Rancho Santa Fe Road across from Wal-Mart and many of its residents have criticized the retailer's plans.

Schaffer said the signals will improve access to the community. Now, turning onto Rancho Santa Fe Road can be hair-raising and drivers must often wait several minutes for an opening.

But Stailey doesn't think the traffic lights needed as a result of Wal-Mart will do anything to relieve gridlock on Rancho Santa Fe Road. He says the city's traffic estimates are misleading.

For instance, the city estimates that only 4,400 new drivers will use Rancho Santa Fe Road each day as a result of the Wal-Mart. Add that to nearly 6,000 drivers already on the road who are expected to stop at the store on their way through the area. So in reality, 10,000 cars will visit the 139,000-square-foot store each day, the city's studies show.

Stailey says he doesn't care if drivers got in their car with Wal-Mart on their brain or decided to stop on the spur of the moment on the way home. The end result will be the same -- 10,000 cars visiting the store, creating noise and worsening gridlock in an already congested area.

"If you live there or drive through there, does it matter where the cars come from?" he asked rhetorically.

The city's study shows a decrease in overall traffic, but it doesn't consider the impacts of having 10,000 cars a day visiting the giant store, because it only considers the 4,400 new cars visiting the store.

"Whenever they talk about numbers, they're talking about the whole project," he said, referring to the entire University Commons development project. In order to accommodate the store, the council rezoned a 20-acre residential parcel that was slated for about 300 apartments for commercial use. Other changes included making 12.8 acres of industrial land into a mix of industrial and multifamily housing.

When the city talks about the impact of traffic, they talk not just about Wal-Mart, but all the changes planned for University Commons. "They want to lump it all together … It's not a fair representation," Stailey. He also said the widened road will still be insufficient.

"It doesn't matter how wide you make the road, you'll never get it out of gridlock," Stailey said.

San Marcos City Engineer Gena Franco said Rancho Santa Fe Road will go from a failing service level "F" to an acceptable service level of "D" when the widening is completed. That level has some congestion, but not as much as gridlock that comes with "E" and "F" ratings. The top rating is "A" and roads can also be rated with a "B" or "C," which Franco said is the ideal.

She said the city used standards set by the San Diego Association of Governments to determine how many new drivers would flock to the area because of Wal-Mart.

The study also notes that a number of road improvements in Carlsbad are planned over the next several years including the widening of Palomar Airport Road and improvements to Poinsettia Road, which Franco said "will have a very positive impact" on San Marcos traffic.

"The volumes will actually drop once some of these improvements are in there," she said.

But if the traffic projects are delayed, which she doesn't think will happen, traffic models don't show Rancho Santa Fe Road dropping from a level of D until 2010, she said.

A forum on Wal-Mart will be held Wednesday at 5:30 p.m. at the San Marcos Senior Center, 111 Richmar Ave. For information, call the San Marcos Chamber of Commerce at (760) 744-1270.

Contact staff writer Katherine Marks at (760) 761-4411 or kmarks@nctimes.com.