Answer: The US and Mexico

The US-Mexico border is the subject of endless debate and scrutiny in both political and reporting circles thanks to concerns over illegal immigration, but very little is said about how the border between the two countries is actually the site of the largest number of legal border crossings per year.

The 1,954 mile long continental border is the site of a whopping 350 million legal crossings per year with 50 million of those crossings occurring in the population heavy area surrounding the San Diego/Tijuana border (2005 statistics).

Among those filtering back and forth across the border are a wide range of workers and students. A study in 1999 revealed that 7.6 percent of the labor force of Tijuana was employed in the city of San Diego.