One of the most significant differences between land-based QSs and airport-based stations is the large volume of land border crossings relative to entries at airports and seaports. According to the U.S. Department of Transportation, legal entries into the U.S. numbered more than 319 million at 163 land border ports of entry in 2005, representing 74% of all international entries.2,3
The combined numbers of airport and seaport entries in 2005 were 80 million and 26 million, respectively. Almost 95 million (30%) international land border crossings occur at the two San Diego and four El Paso ports of entry (, ). San Diego's San Ysidro port of entry is the world's most frequently crossed international port of entry, with more than 41 million northbound crossings each year, constituting 10% of all land, sea, and air U.S. entries. Entries through airports and seaports from Mexico into the southern border region totaled less than 4.8 million in 2005.
Fifteen most highly utilized U.S. land border ports of entry, 2005
Map of major U.S. land border ports of entry
A sizable portion of land border crossings is attributable to people who cross daily or regularly to shop, visit family, or do work or business in U.S. sister-city communities. Others are permanent immigrants, travelers, legal migrant workers, and students crossing land borders to reside in U.S. territory permanently or for an extended period. Unlike travelers at airports and seaports, the vast majority of entrants use private vehicles. The remainder cross as pedestrians (especially to and from metropolitan sister cities on the U.S.-Mexico border), arrive by bus, or, least commonly, by train. According to the U.S. Department of Transportation, more than 3.7 million bus passengers enter the U.S. from Mexico each year. Incoming truck traffic from Mexico totaled 4.6 million vehicles in 2005, with 1.5 million trucks crossing at Laredo, Texas; 741,000 at El Paso; and 730,000 at Otay Mesa/San Diego.
At the U.S.-Canada border, approximately 74 million people entered the U.S. in 2005. The three busiest crossing points were Buffalo-Niagara Falls, New York (16.1 million), Detroit (13.3 million), and Blaine, Washington (5.6 million). Certain characteristics, such as the large volume of cross-border commuters and the substantial flow of individual travelers and freight, are similar at both northern and southern U.S. borders. However, public health issues at the Canadian border differ from those at the U.S. southern border because of relatively prosperous socioeconomic conditions in Canada and the substantial public health infrastructure there.
The unauthorized border-crossing population is understandably less well characterized. In 2006, U.S. Customs and Border Protection (CBP) estimated 11.6 million undocumented aliens were living in the United States.4
Of these, an estimated 4.2 million had entered in 2000 or later and an estimated 6.6 million were from Mexico. About 7.2 million were employed in March 2005, accounting for roughly 5% of the civilian labor force. Most reside in border states in the Southwest. Others live throughout the United States, working as migrant laborers in urban areas such as New York, Chicago, and Atlanta, and in rural areas of Washington State, North Carolina, Kansas, and elsewhere. In 2005, CBP reported the apprehension of almost 1.2 million undocumented aliens crossing the U.S.-Mexico border.5
Most (86%) detainees were Mexican nationals, an additional 10% were from Central America, and nearly 3% were from Brazil. Countries in the eastern hemisphere, including China, accounted for less than 1%.