Every year more than a million people flee the poverty of their own countries, crossing the river at the border between Guatemala and Mexico, and try their luck, on this road to what some call the impossible dream.

Men and women from Salvador, Honduras or Nicaragua are crossing the river into Mexico illegally - and they have another destination in mind: the US.

To reach the border with Texas, they have to cross the whole of Mexico, a journey of 2,500 miles. And a journey which for most heading North begins at the Arriaga train station.

Regardless of the danger, each one tries to find himself a little spot on the freight trains: on the roofs, on the axles between the cars, there can be as many as 1,000 hitching a ride.

But in order to arrest the maximum of illegal immigrants, the police stops the train in the middle of the countryside.

We follow four young Salvadorian immigrants who jump from train to train in a journey fraught with danger as they attempt to reach the promised land of the US.