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3 is a magic number

It’s greater than 4 and sometimes equal to 5

Folsom St, Boulder (photo: Community Cycles)

When it comes to traffic and streets, some things just don’t add up at first glance.

Recent right-sizing road projects in Boulder, Pueblo and Fort Collins attracted media attention and spirited discussions during public meetings.

Logically, if 2 lanes are good (for moving people) then 4 lanes are twice as good! Right?

Only something strange can happen as we get to roads with 4 lanes or more…people begin to disappear. (I don’t mean in an alien-abduction sense.) Fewer people feel safe walking or biking on that big, wide road. They avoid that route and often are afraid to even let their children cross it.

This results in more short trips (3 miles or less) being taken by car, which in turn creates more congestion on the wide road, which in turn creates demand for even more lanes. Do you see where this is going?

Here’s where the magic number 3 comes in

Folsom St, Boulder (photo: Community Cycles)

When a 4-lane road is resized into a 3-lane design, just as many cars can get through the corridor. Left-hand turns can become easier. Speeds can become safer. And people begin to reappear.

This doesn’t make sense at first glance. Folks assume fewer lanes should mean more congestion and more crashes.

Turns out, a few “magical” things are at work. First, traffic in both directions doesn’t get stopped at intersections waiting for people making left turns to get across. This results in more “green light time” for getting along the road.

Second, there are far fewer crashes that clog up the road, especially during rush hour. The Federal Highway Administration reported a 19 percent to 47 percent reduction in overall crashes where right-sizing projects occurred across the country.

Sometimes 3 really equals 5

Then there are all the people who switch their car trips to bike or walk trips because the road includes a place for them and is easier to cross. Adding 2 bike lanes to the 3 travel lanes really gives you 5 paths to travel along the road. More options = more people.

Still doesn’t make sense? Then check out the latest study on 37 different right-sizing projects in Austin, Texas. “With right-sizing, the traffic stream flows more smoothly,” said Randy Machemehl, a civil engineering professor at The University of Texas.


(diagram: Federal Highway Administration)

A Solution for Colorado

It is counter-intuitive to say a 3-lane road is going to work better for the community than a typical 4-lane road. That is why we applaud Colorado communities that are giving right-sizing a try. Once people get to see how the road works, then it will all add up.

Dan Grunig

About the Author: Dan Grunig

Dan directs our organization’s efforts. Transportation and land use policies are his specialty. Gaining equal rights for people who bike is his passion. He loves Colorado because every part of the state is an amazing place to visit and ride. He commutes to work on his bike and rides the roads and trails for fun.


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