It is incredible that more than six years has passed since our lives were so dramatically changed on Sept. 11, 2001, and with it our country’s attitude toward our international borders and measures of security implemented to keep out potential terrorists. Prior to that infamous day, the border crossing concerns were the interdiction of drugs and the undocumented.

Since then, the primary mission of the Department of Homeland Security, organized in the attack’s aftermath, has been to secure the borders from further terrorist infiltration. (The terrorists had legally entered the United States through land and air ports.)

A major new step in that security effort takes effect Jan. 31 that has the potential to dramatically impact San Diego’s social and economic relationship with Baja California.

Known as the Western Hemisphere Travel Initiative (WHTI), this law will require U.S. citizens 19 and over to present a government-issued photo ID such as a driver’s license, and proof of citizenship, such as a birth certificate, naturalization certificate or passport to enter the United States by land or sea.

A passport or NEXUS, SENTRI or FAST card will be accepted as ID and citizenship requirements. Border Crossing Cards will continue to be accepted documents for Mexican citizens to meet both requirements.

WHTI affects travel between the United States and Canada, Mexico, Bermuda and the Caribbean.

When the law was announced, it sent shock waves along both north and south border regions whose populations, in great numbers, daily cross the border for shopping, business or social occasions.

Of course, passing such a sweeping law and gearing up to manage the logistics are two very different animals. We can be generous and say lawmakers did not fully realize the magnitude of border travel. In San Diego we are familiar with the primary number: more than 60 million people cross the border annually at the ports-of-entry at San Ysidro, Otay Mesa and Tecate. For perspective, this number represents nearly the combined populations of California, Arizona, New Mexico and Texas. And it only tells part of the enormity of border activity.

The United States has 326 official ports-of-entry through which each day more than 1.1 million (401.5 million annually) travelers enter or re-enter, including 327,000 cars (119.4 million annually) and more than 18,000 commercial trucks (17.1 million annually).

Requiring passports is not the sole new way to track visitors. Another law mandates that these documents be biometric, outfitted with an RFID chip that wirelessly can transmit information about the bearer, including fingerprints. It was a nice idea, but beyond the capability of technology and personnel to handle at the scale of legal border crossings.

To top it off, fewer than 20 percent of Americans had passports when the WHTI was passed. This led to a flood of applications that bogged down passport issuance. The number of passports issued has risen from 7 million in 2002 to 7.3 million in 2003, 8.8 million in 2004, 10.1 million in 2005 and 12.1 million in 2006. Great progress, but the total issued is still less than 30 percent of the population.

As the magnitude of meeting WHTI requirements became obvious, the effective date was delayed. For air travel, it finally became effective on Jan. 23 of this year.

For those in cars or on foot crossing the border back into the United States, the historical practice of accepting oral declarations alone (Question: Citizenship? Answer: U.S.) will end, effective Jan. 31.

Additional requirements, however, will be gradual.

The Department of Homeland Security expects that by summer the equipment and training will be in place so that full implementation of WHTI requirements will take effect for all land and sea entries. (The precise date will be announced with at least 60 days notice.) As this column has reported, the border regions of San Diego and Baja are economically integrated far more than most San Diegans care to admit. Border crossing delays already cause $8.5 billion in economic disruptions a year, according to a recent study by the San Diego Association of Governments and California Department of Transportation.

Sadly, information about these new requirements has been woefully underreported and explained. For many it will be a shock, followed by either the wait it takes to get a passport or a simple abandonment of the idea of even crossing the border. At a time of economic slowing, doing business with our best partner in a global world likely will take a hit. Then again, Washington politicians already have shrugged off the $8.5 billion in ongoing economic losses. What’s another few million or billion to San Diego mean to them?

Patrick Osio Jr. can be reached at posiojr@sandiegometro.com. The veteran consultant also has issued The Mexican Perspective, an intensive primer on business culture and protocol. Copies are available at hispanicvista.com/sales/book_sale.htm.