
The Mexico-U.S. border wall at Tijuana, Mexico. Photo © Tomas Castelazo / Wikimedia Commons / CC BY-SA
The border crossing in this direction is a busy place. A long line of cars and buses takes hours to get to the front of the line on a good day and, due to the interminable inching forward, vehicles tend to keep their motors running, making the air full of exhaust fumes.
A steel post announces “United States”, with “Welcome” engraved into its base in English, Japanese, Thai, German and other languages. Tens of millions of people cross this border annually, from Tijuana, Mexico into San Diego, United States.