We leave Altar for the remote border town of El Sasabe, where the migrant hopefuls start their walk into the United States. “You are going into the lion’s den”, says a coyote with five years in the trade, whom we meet eating his meat tacos at a roadside restaurant and who talks about those who have died trying to cross the desert.

That doesn’t seem to put anyone off. At midday in Altar, the rusting brown and white Ford vans that shift up to 1,500 migrants a day up to the border cough into life. They pack in the people. With bare metal benches running up each side of the vans and a bench up the middle, about 20 grown men crouch inside each vehicle for the hot, bumpy, three-hour ride to the border. Cost of a ticket: 100 pesos ($9.00) each.

Tim tries to talk his way into letting a driver take him with the migrants. Raising suspicions that the tall white gringo might be from the migra or just completely mad, he is rejected, so Tim takes his pick up truck and Tomas and I drive the hire car. We turn off the paved highway. A rusted sign saying “Sasabe” points us down a wide dirt road through the desert.

At a concrete hut, we pay 30 pesos ($2.50) to a old man in white cowboy hat. He lifts up the chain.

We feel shaken to bits by the furrowed road. Our wheels skid in the sand. The dust blinds our windshield. Dozens of vans hurry past us, their worn tires bouncing in and out of pot holes as they barrel down illegal immigration’s superhighway.

Until they arrive at the lake in the middle of the road, that is. One by one, the vans rock through a chocolate brown mess of mud, tire tracks and water from the heavy rains the night before. Tim’s truck makes it through easily.I, in the pathetically unsuitable hire vehicle, try.I rev through the sticky soup, hold the steering wheel steady.I get stuck, my wheels spin and the chassis sinks into the mud.

Two men wander over with a chain and offer to haul us out, but there is nowhere to attach the chain, so I try to reverse, get some traction and have another try. I make it out.

Tim gets a puncture. We fix it in the searing heat and it is some comfort to see a handleful of vans along the route with tire problems too.

We pass rusted wrecks of abandoned cars in the desert, rubbish, empty water bottles, dead animals and migrants with candles to Mexico’s most hallowed saint, the Virgin of Guadelupe. We rumble into El Sasabe.