Traffic and Health Effects

The Houston area is in a neck and neck race with Los Angeles for the worst ozone smog in the country. Although the majority of the pollutants that combine to make ozone in the Houston area come from industry, increasing the capacity of major roads to carry more vehicles does not improve our prognosis for clean air. Moreover, ozone smog isn't the only pollution problem we need to be concerned about when we will be adding millions of vehicle miles traveled (VMT) per day.

Pollution caused by cars and trucks includes more than what is measured at the tailpipe during an emissions test. We also breathe in evaporative emissions from engines and unburned fuel; fine particles from the deterioration of tires, concrete, and asphalt; evaporative emissions from pavement; emissions from fuel leaks and spills; emissions from fueling vehicles; and platinum from catalytic converters.

There are consequences to living near heavily traveled roadways and breathing in all those emissions. Several studies suggest that there is an association between living near heavy traffic and an increased incidence of childhood cancer. A study in Denver found that children with leukemia were eight times more likely to live close to highways with 20,000 or more vehicles per day than children without leukemia. (See box for a comparison with Houston area highways.) Researchers in Denmark reported a 25% increase in lymphoma correlated with living near heavy traffic.

Higher rates of allergies, cough, and respiratory symptoms in children have also been correlated with living within 100 yards of a freeway. Another study found that children who live within 500 yards of heavy traffic (identified as more than 24,000 vehicles in 24 hours) were significantly more likely to be admitted to an area hospital for asthma. Children who attend school near a heavily trafficked roadway have increased respiratory infections and symptoms and increased inflammatory markers according to a 2001 study.

Even the unborn can suffer from freeway air pollution. In the first study to link air pollution with birth defects, researchers at UCLA reported that pregnant women were three times more likely to deliver babies with defective heart valves and cleft lips and palates if the mothers had been exposed to high levels of ozone or carbon monoxide during the second month of pregnancy.

Babies and children are not the only ones affected by living near a major highway. According to a study in the Los Angeles basin, the risk of cancer is higher for people living within 1.2 miles of a major highway and is greatest at 300 to 400 yards from the roadway.

People who live near freeways would seem to suffer the most health impacts of everyone else's exhaust. But anyone driving or riding on a freeway has an increased exposure to vehicle pollution. In-car exposures to carbon monoxide, benzene, and fine particulate matter are often two to ten times higher than roadside measurements.

Several highway expansion projects are in varying stages of construction and planning in the Houston area: the Westpark Tollway, Katy Freeway (I-10 West), Highway 290, and the Grand Parkway. Very little thought has been given to the long-term consequences of these projects or to incorporating mass transit into them. Find out what one group is doing to fight this senseless paving over of our landscape at www.katycorridor.org.

24-Hour Annual Traffic Count Averages