While in Mexico City formal jobs are concentrated in the city centre, affordable housing is generally only available in its outer rings. This reduced accessibility to formal employment would suggest that the poor have longer commutes. However, observed travel times show that low-income workers actually have the shortest commutes. Using two linear programming transportation models we found that this is due to the location of informal work activities, which seems to be a function of the residential location of workers involved in the informal sector as a response to the disadvantages of the formal urban structure of jobs and housing that affect the poor.