Clogged traffic lanes and eternal delays at the official crossings that separate Mexico from San Diego are nothing new to the border landscape.

But a report released Monday by a San Diego civic group offers new insights into just who these people are and what they're doing: An overwhelming majority cross many times each month to work, shop and visit friends and family.

Among them, they spend more than $4 billion a year in San Diego and Tijuana, according to the study. And they're sick of the long, hot lines.

The study, conducted by San Diego Dialogue with the help of student interviewers from Tijuana's Universidad IberoAmericana, offers the first look at just who crosses the border between San Diego and Tijuana and what they contribute to the region's economies.

Already, the border along San Diego's southern edge is the busiest in the world, with more than 52 million cars crossing each year, according to the group. Thousands more cross illegally into San Diego County every day.

With the impending North American Free Trade Agreement, lines at the ports of entry are expected to get worse, and, unless steps are taken to speed up the commute for these big spenders, they may just take their business elsewhere, members of San Diego Dialogue warn.

Commuter lanes that electronically read bar codes on the cars of frequent crossers could speed things up, suggested Charles Nathanson, executive director of San Diego Dialogue, a collection of business leaders, media representatives and academics from both sides of the border.

"There's thousands of people who want to come here and spend money, and shop and shop and shop, and we're keeping the doors locked," Nathanson said.

The researchers interviewed more than 5,000 legal border crossers this summer at the San Ysidro and Otay Mesa crossings. About 230,000 San Diego and Tijuana residents cross once a week or more, making 4 million trips a month and accounting for 97% of all vehicle crossings, the group found.

About 103,000 people cross 20 times a month or more, making more than 3 million monthly trips and accounting for 74% of the total traffic.

Many of those interviewed said they spend hours in line at the U.S. Customs and Immigration and Naturalization Service inspection lanes, head researcher Millicent Cox said.

The study has broken down some of the border's persistent stereotypes, she said.