The big picture: Car Poolers, by Alejandro Cartagena

Highway 85, otherwise known as Gonzalitos, bisects Monterrey and its nine adjoining cities in north-east Mexico. → Photograph: Alejandro Cartagena

Highway 85 links the city centre and its wealthier parts with the vast suburban sprawl surrounding this metropolitan area – the third largest in Mexico. → Photograph: Alejandro Cartagena

House-building is big business in Mexico, and suburbs are booming, their rapid expansion encouraged by the government and unhampered by environmental or societal concerns. → Photograph: Alejandro Cartagena

Public transport is poor and expensive, so these construction workers hitch an early-morning ride to work in the back of their contractors’ trucks. → Photograph: Alejandro Cartagena

It’s part of the deal when they get the job – otherwise, up to a quarter of their average daily wage of 400 pesos (around £20) would be eaten up on bus fares. → Photograph: Alejandro Cartagena

The trucks are uncomfortable and cold, so it’s easier if you have a blanket to ward off the early-morning chill. →
Photograph: Alejandro Cartagena

They will be digging swimming pools, landscaping gardens and building homes for the wealthy on the other side of the city. → Photograph: Alejandro Cartagena

Photographer Alejandro Cartagena, who is himself from Monterrey, positioned himself on a footbridge above the highway, his bird’s-eye shots usually catching these commuters unawares. → Photograph: Alejandro Cartagena

Days are long, and work is hard, so for many the drive, which in bad traffic can take an hour and a half, is a chance to go back to sleep. → Photograph: Alejandro Cartagena

As a child, Cartagena hitched rides in much the same way. → Photograph: Alejandro Cartagena

This project continues Cartagena’s studies of the effects of suburban sprawl on population growth and the environment in his home city. → Photograph: Alejandro Cartagena

They probably don’t consider it, of course, but by sharing lifts through economic necessity, these men are in their own small way helping to reduce the impact of increased traffic and pollution. Photograph: Alejandro Cartagena