The San Ysidro border crossing between Mexico and the United States is the world's busiest border crossing and handles 125,000 people per day. This show highlights some of the difficulties o... Read allThe San Ysidro border crossing between Mexico and the United States is the world's busiest border crossing and handles 125,000 people per day. This show highlights some of the difficulties operating such a busy crossing.The San Ysidro border crossing between Mexico and the United States is the world's busiest border crossing and handles 125,000 people per day. This show highlights some of the difficulties operating such a busy crossing.