How Traffic Jams Affect Air Quality

by | Jan 5, 2012

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No one will be surprised to learn that areas with the largest number of cars on the road see higher levels of air pollution on average. Motor vehicles are one of the largest sources of pollution worldwide. You may be surprised to learn, however, that slower moving traffic emits more pollution than when cars move at freeway speeds. Traffic jams are bad for our air.

Freeway Speed and Air Quality

It seems intuitive that your car burns more fuel the faster you go. But the truth is that your car burns the most fuel while accelerating to get up to speed. Maintaining a constant speed against wind-resistance burns more or less a constant amount. It’s when you find yourself in a sea of orange traffic cones — stuck in what looks more like a parking lot than a highway — that your car really starts eating up gas. The constant acceleration and braking of stop-and-go traffic burns more gas, and therefore pumps more pollutants into the air.

The relationship between driving speed and pollution isn’t perfectly linear, though. One study suggests that emissions start to go up when average freeway speed dips below 45 miles per hour (mph). They also start to go up dramatically as the average speed goes above 65 mph. So, the “golden zone” for fuel-consumption and emissions from your vehicle may be somewhere between 45 and 65 mph.

This leads to a dilemma for urban planners trying to develop roadways that will reduce congestion with an eye to reducing the pollution that it causes. Laying out the traffic cones for massive freeway expansion projects sends air-quality plummeting, but the hope is that air-quality will improve somewhat once the cones are gone and everyone is cruising along happily at regular freeway speeds. Ironically, since the average freeway speeds for non-congested traffic hover around 70 mph and above (with states like Texas looking to increase their speed limits), air-quality is unlikely to improve — and may actually worsen — once those highway improvements are finished.

Types of Air Pollution

The effects of pollutants found in vehicle exhaust are significant for people living in urban areas. High levels of nitrogen oxide are toxic to humans. Sulfur dioxide is the primary cause of acid rain. Carbon dioxide contributes to climate change by insulating more heat from the sun. And ozone can impair lung function, especially in children and adults with asthma, with a higher number of sufferers resulting in high-traffic urban areas.

Cities Try to Tackle Traffic Pollution

The solutions to reducing or eliminating traffic as a source of pollution aren’t really that innovative. Cities that invest heavily in public transit can see dividends in the form of fewer cars on the road. Many people are loathe to give up the freedom of their own vehicles, but rising gas prices often help to encourage good numbers of drivers to make the switch to the subway, light-rail or the bus. Employers can help take cars off of the road by offering incentives to employees who take public transit or carpool as well.

Still, even with effective public transit, air-quality problems persist in many areas. Cities like London have begun charging tolls to drivers who access high-congestion areas of the city during peak traffic times. Car-share companies have also started to see success in dense urban areas, spreading the cost of car ownership and — hopefully — emissions across a wider number of people, reducing trips, mileage and pollution.

Advancing Technology Helps Reduce Emissions

We’ve already seen a large reduction in the rate of emissions generated by a single vehicle, thanks largely to improved car engine designs, catalytic-converters and improved fuel chemistry. On the horizon, we can look forward to the increasing popularity of hybrid and electric technology for personal vehicles.

The challenges of these types of technology is that they are far from perfect and may just shift the pollution to a separate place in the energy chain. Electric cars, for example, simply get their energy from the electrical grid, which is generated largely by coal-burning power plants, generating its own pollutants in mining and eventual burning of coal. If cleaner sources of electricity can be brought effectively to market, such as solar power, we may be able to avoid millions of tons of emissions.

All of these solutions can help mitigate the impact of traffic on our air-quality, though they’ll undoubtedly need to be combined with other strategies for cleaning up our air. Public transit and smart-driving can do a lot to reduce emissions and clear the air. Likewise, seeing smarter construction projects, ones that improve the efficiency of our highway systems by reducing stop-and-go traffic, will go a long way to get cars moving without simply inviting even more cars onto the road. In the end, contributions from conscientious drivers, innovative technology and wise city-planning will help us all breathe a little easier.

Paul Sanders is lead writer for Trans-Supply, which offers the best deals on traffic safety supplies, such as traffic cones and barricades, as well as airport, construction and railroad products.

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