Atlanta’s I-85 Collapse — Another “Carmaggedon” That Wasn’t

There was no congestion crisis on the Atlanta highway system this morning. Image:
There was no congestion crisis on the Atlanta highway system this morning. Image: Google Maps via City Observatory

Few cities are built around highways more than Atlanta. So when a heavily-traveled section of I-85 collapsed in a fire last week, the traffic predictions were dire.

A few days into this rearrangement of the local highway system, however, Atlantans are adjusting their travel behavior in ways that keep gridlock at bay. MARTA ridership is up 25 percent, for example.

While it’s still early going, the I-85 collapse appears to be another case of “carmaggedon” that never materialized — and that should inform the way we plan our transportation systems, writes Joe Cortright at City Observatory:

Arguably, our mental model of traffic is just wrong. We tend to think of traffic volumes, and trip-making generally as inexorable forces of nature. The diurnal flow of 250,000 vehicles a day on an urban freeway like I-85 is just as regular and predictable as the tides.What this misses is that there’s a deep behavioral basis to travel. Human beings will shift their behavior in response to changing circumstances. If road capacity is impaired, many people can decide not to travel, change when they travel, change where they travel, or even change their mode of travel. The fact that Carmageddon almost never comes is powerful evidence of induced demand: people travel on roadways because the capacity is available for their trips, when when the capacity goes away, so does much of the trip making.

If Atlanta can survive for a month or two without a major chunk of its freeway, that’s a powerful indication that more modest steps to alter road capacity don’t really mean the end of the world. If we recognize that traffic will tend to adjust to available capacity, we then end up taking a different view of how to balance transportation against other objectives. For example, this ought to be a signal that road diets, which have been shown to greatly improve safety and encourage walking and cycling, don’t have anything approaching the kinds of adverse effects on travel that highway engineers usually predict. So in the next few weeks, keep an eye on Atlanta: If the one of the nation’s most sprawling and traffic ridden cities can survive the loss of a freeway segment that carries a quarter million vehicles a day, its a strong sign that more modest changes to road systems really don’t have much impact on metropolitan prosperity.

More recommended reading today: The State Smart Transportation Initiative reports on how fire codes are interfering with safe street design in Celebration, Florida. And Pedestrian Observations considers the proper ratio of branch lines to trunk lines in a transit network.

  • betty barcode

    Well said. Traffic expands or contracts to fill available space. Thus, communities should decide how much real estate to devote solely to the automobile and how much real estate should serve other needs.

  • Vooch

    Angie wrote another brilliant article !

  • dmcfa

    Nothing mentions that Atlanta public schools are out this week for spring break. School goes back in session next week.
    Jump in Public Transportation already is impressive. Park & Ride locations full.

  • thielges

    San Francisco had a similar unplanned experiment when the 1989 Loma Prieta earthquake damaged the Embarcadero Freeway (CA-480) along with some other spurs off of I-80. Residents expected doom but after the rubble was cleared everybody adapted to the new configuration. While it does take a few more minutes to drive from the Marina, North Beach, and Chinatown neighborhoods to the freeway, the overall change is a big positive. No longer is the waterfront by the Ferry Building in the gloomy shade of a double decker elevated freeway. The Bay waterfront went from a soulless gritty dump to a vibrant place where people now actually seek as a destination.

  • Vooch

    Superhighways are a blight on every city. They should all be removed and original street restored

  • frank jones

    If the North East section of the Atlanta metro area had a commuter line from Gainesville to downtown Atlanta on the NS line then many of the regular automobile travelers on both Ga 400 & I-85 could have made a quick commute into Atlanta. The only item would be the need for bus services to rail line.

  • oceanstater

    Too late to help Providence where the state decided to replace a crumbling urban expressway that blights a neighborhood just to the west of downtown Providence rather than replace it with a much cheaper surface boulevard due to fear of interfering with the high traffic volumes, and, fear of suburban motorists who just want to tear thru the city. Maybe the future belongs to those willing to rethink these urban highway nightmares.

  • Ansel Lundberg

    It’s a shame that it took a fire to destroy the freeway in Atlanta and an earthquake to remove the one in SF… it’s hard to wish a disaster on my own city, but I don’t know any other way to remove the freeways that are strangling it!

  • ct

    Another way of looking at it: the Atlanta downtown core is just not that vital to the metro area. Even within the Atlanta city limits, not all high-rise office structures are downtown. The reason why metro Atlanta didn’t melt down is its sprawl.

  • goodwillhinton

    I’m sorry but you have zero pertinent data to make these assertions and don’t understand the facts on the ground. All public school systems in Atlanta are on spring break this week. As such, any traffic measurements are way undercounted this week. Even with the greatly reduced traffic due to schools being out, there are massive increases in traffic. One arterial road near the freeway collapse usually get 15k people in the mornings but this week has had 40k. Unless you are on the ground here and getting actually data and understand the situation, you can’t make any claims about what this does or doesn’t mean. Try again in a couple weeks if you want to show some intellectual honesty and proper journalism.

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