Travelling along the Mexico-U.S. border, the world's most dangerous land route for migrants

W5 | Narco Jungle: The Death Train, Part 3 The infamous U.S.-Mexico wall begins off the coast of Tijuana and stretches roughly 3,000 kilometres. This is how the cartels exploit it.

This is part three of a five-part series following the harrowing journeys of migrants who risk their lives crossing the Darien Gap and riding atop Mexico's notorious 'Train of Death.' W5 Investigative Unit Managing Editor and Senior Correspondent Avery Haines follows migrants as they travel across the Mexico-U.S. border.

The Mexico-U.S. border is the world’s most dangerous land crossing for migrants.

Hundreds die every year in the desert. It stretches almost 3,000 kilometres along four American states.

This map shows where there are fences and barriers, and where there are none.

I travelled the length of the border, in my search for migrant families I met six months ago when I trekked from Colombia to Panama in the Darien Gap for the W5 documentary, "Narco Jungle."

Follow my journey across Mexico in this interactive map below, from the very eastern border to the far west, and an emotional reunion with two young girls we rescued in the jungle.

For a full-screen view of the map interactive, click here.