Today’s post is by Leslie Valentine, an editor and writer at Environmental Defense.

When I visit friends and family in other places, whether it’s Portland or Los Angeles, Austin or New York City, I’m always struck by how traffic and commuting inevitably come up in conversation.

Those who live in the central core of a city are grateful they don’t have far to drive, or can walk or ’sub’ it to work. Others trade stories of commutes from hell, driving in bumper-to-bumper traffic on the main route into downtown. Everyone laments how it seems to be getting worse and worse every year in these lively, growing places.

Many growing cities and towns are traffic-choked and plagued by pollution. But population growth accounts for only a small share of increasing road traffic in recent decades.

What’s really going on is that Americans are driving more: We are taking more trips on motorways, making longer trips and driving alone more. More people live in car-dependent suburbs not conducive to walking or transit.

Sadly, incentives are skewed toward car use: "freeways" subsidized by general tax revenue, "free" parking paid for by employers, low mileage drivers subsidizing insurance costs for high mileage drivers, and countless policies favoring low density sprawl over infill mixed-use development. (Read more about our broken transportation system.)

But this has to change. We can’t keep building our way out of traffic jams and pollution with more roads and highways – it just doesn’t work. And the costs to our health and quality of life are too high. Our transportation experts at Environmental Defense have long studied the problems and are working on smart solutions. (Read more about solutions to traffic problems.)

One key is to use existing infrastructure much more efficiently. Incentives like congestion pricing and bus rapid transit lanes are two ways to get traffic moving. With tools like these in place, an existing highway can move more people more quickly with less environmental damage.

Says Environmental Defense regional director Andy Darrell: "Our country is growing, and we’ll always be building something new. The key is to build new communities in ways that decrease dependence on the traditional car and increase opportunities for walking, cycling and innovations like car-sharing, advanced vehicle technologies and new ideas for transit."

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