The polluted city of Houston gained some relief in January 2004 with the opening of a light rail system.

Texas’s largest city, which now boasts a gas mask as its unofficial emblem, has been without a local rail service for an amazing 64 years but voters rebelled against conservative politicians who tried to halt the plans to bring back rail.

A long series of contentious elections, funding controversies and political disputes has kept the city dependent on cars and buses and contributed to a smog problem that has made Houston second only to Los Angeles in air pollution, according to government statistics.

Experts blame about 50 per cent of the city's smog on vehicle exhausts. Conservative groups fought bitterly to stop the rail system by filing lawsuits and forcing a recent election, which they lost when voters approved the rail system.

One of the local heroes has been Texas Republican Senator Kay Bailey Hutchison, one of the few leaders in the Republican-dominated State to push for federal rail funds. She assured rail supporters federal money would flow as the system was built.

Houston's Metropolitan Transit Authority spent £190million over the past three years constructing the 7.5-mile line that is the centrepiece in a planned 80-mile system.

Houston was the last major metropolitan area in the United States without light rail trains.

The Galveston-Houston Association for Smog Prevention - GHASP - is calling for a 55mph top speed limit on the roads as another way of tackling the air pollution.

Little appears to have been done to tackle pollution during the years when George W Bush _ now US president - was governor of Texas.

Dallas is the only other Texas city to have a rail system, which opened in 1996, and now has 44 miles of lines.