Street Widening Ad Infinitum

Put your thinking caps on kids, because today's lesson in transportation planning is brought to you by the letter I and number 6.

A new report by Todd Litman of the Victoria Transport Policy Institute titled Generated Traffic and Induced Travel - Implications for Transport Planning is about something called "generated traffic". Forgive the geeky transport talk, but according to the paper:

"Traffic congestion tends to maintain equilibrium. Congestion reaches a point at which it constrains further growth in peak-period [i.e., rush hour] trips. If road capacity increases, the number of peak-period trips also increases until congestion again limits further traffic growth. The additional travel is called “generated traffic.” Generated traffic consists of diverted traffic (trips shifted in time, route and destination), and induced vehicle travel (shifts from other modes, longer trips and new vehicle trips). Research indicates that generated traffic often fills a significant portion of capacity added to congested urban road."

After years of street widening construction, the street is much better to drive on because it's wider and traffic moves. But then have you ever noticed that a short time later, maybe just a couple of years, the street gets so congested again and traffic is nearly as bad as it was before the widening. What gives?! This is because others figured out the street was less congested and started driving on it too. But there were too many of them who did this. What to do? Expand it again! Then again! And again (ad infinitum)! It's only money and more congestion we're talking about. The benefits of widening I-66, or the "spot improvements" misnomer the project has been given, would only last a short time.

There's a choice and it's making itself clearer than ever before. Transportation demand management looks at lowering the demand for a street, not increasing its supply by widening it. Lowering the demand of a street includes providing increased transit service, creating bike and walk infrastructure so people have safe places to ride and walk, telework, and downtown congestion charging. These could be less expensive to do than street widening with the results lasting much longer.

Paul DeMaio, BikeArlington