The collapse of rural areas in the country's south drives urban migration. Finally, poverty and unemployment have risen throughout rural Mexico. Rapid urbanization has created a slew of issues in Mexico City. Despite the fact that Mexico City is growing, there is still a lack of land and homes. In addition, pollution is becoming a problem as more people move to the city center. Rural exodus and economic hardship have caused Mexico City's population to rise rapidly over the past few decades. In 1970, the metropolitan area had about 9 million residents; today it's estimated to be over 20 million. This increase is expected to continue, since recent government policies aim to promote urban living and discourage moving to large cities from small towns and rural areas. Mexico City is a major metropolis, but it lacks the resources of other mega-cities worldwide. For example, it has no ocean port or airport, which prevents it from engaging in trade with other countries. Instead, it relies on neighboring states for employment and investment. The city's poor infrastructure has also led to environmental damage. Since most industries are located in southern Mexico City, there is heavy traffic congestion during the morning and evening rush hours. There are plans to build more public transportation, but this will take time given the shortage of funds. Mexico City has one of the highest crime rates in the world.