Does TTI underestimate historic congestion levels?

To read the Texas Transportation Institute’s Urban Mobility Report is to believe congestion has more than doubled since 1982 (really between 1982 and 2000). From one perspective, of course congestion must have risen, demand (Vehicle Miles Traveled, Population, etc.) increased significantly over this period while supply (Lane Miles of Road Capacity) did not increase at nearly the same rate.
But I was alive in 1982, I was in cars at that age (and driving myself the next year) (in Central Maryland). I remember congestion in the 1980s. To misquote Lloyd Bentsen, “Congestion was a friend of mine”, and TTI seems to be saying to 1982 “You’re no congestion”. But congestion doesn’t seem appreciably different from today. People complained about it then as much as now. Some bottlenecks have been fixed, new ones have emerged.
So I wonder whether congestion did, in fact, “double”.
Some hypotheses:
1. Measurement issues. Continuous roadway travel time measurements were a lot scarcer in the 1980s than today. Freeways now have loop detectors on every segment, whereas there might have been a permanent recording station every 5 or 10 miles in the 1980s, so a lot more had to be estimated and approximated. There are still no good arterial measurements, the most recent Urban Mobility Report uses GPS data from Inrix, and this will clearly come to dominate congestion measures. Notably, including this measurement forced TTI to re-estimate downward their historical congestion measurements.
2. Definition: As noted by Joe Cortright’s report Driven Apart, mobility is not accessibility. A city where I can reach everything in 10 minutes, but travel at 30 MPH (when freeflow is 60 MPH) is more congested than one where I can reach everything in 30 minutes, but can travel at freeflow conditions. The TTI in a sense penalizes efficient land uses.
3. Induced Demand: Highway expansion tends to get used up (this is not a bad thing of itself, just a thing), so much of road expansion gets eaten up in more traffic. Similarly highway reduction reduces travel. Duranton and Turner write “We conclude that an increased provision of roads or public transit is unlikely to relieve congestion.”
This does not explain why congestion is under-estimated in the past though.
4. Congestion vs. Speed: Travel times on journey to work increased only marginally over this period. Average distances for trips rose faster than travel times, indicating average travel speeds increased. So even with increasing congestion, if travelers shifted to relatively faster (e.g. suburb to suburb freeways) from slower (e.g. suburb to city arterials), congestion can rise on each link, but travel speeds still increase. See The Rational Locator for an example of this.
5. Perspective: This previous point about perception can be refamed as one of perspective. There are differences between spatial averages (which TTI uses) and person-based averages (which individual observers perceive). So the person based average for any metropolitan resident may be the same, but the amount of space (network) covered by congestion may increase if the total amount of space which is developed increases. Similarly, if there is peak spreading, congestion occurs over a longer duration.
However, TTI is not simply saying that the amount of area that is congested increased, they are claiming, for Washington DC the delay per person increased from 20 hours per year in 1982 to 74 hours in 2010.
I am willing to believe that with recent measurements, 74 hours per year for an average commuter in DC is plausible in 2010, since that is just under 10 minutes each way each day for 225 work days per year. 10 minutes of delay on a 30 minute commute means the freeflow time on that commute (un-delayed, e.g. Sunday morning) was 20 minutes. This seems about right for the “average” commuter. Rush hour is when everyone has to slow down.
But this implies in 1982 that delay was less than 3 minutes a day per commuter each way. That seems unreasonably small when you think about it, I could have spent 3 minutes at a traffic light in DC at the time, and that certainly constitutes delay. They are saying for every person who had a 10 minute delay, 2 people had 0 delay to get an average 3 minute delay, and that is not the metropolitan Washington I was familiar with. Congestion was sufficiently important than that radio stations had regular traffic reports, and traffic helicopters, it was not something insignificant.
Of course this is impossible to fully validate, as we cannot go back in time and accurately measure speed. The best I could think of was using the Google NGram feature to track mention of some keywords in books. This proves nothing unfortunately, and suggests a small uptick in the word “traffic” in the 1990s, but is interesting none-the-less.
One however can imagine the motivation for wanting congestion to appear lower in the past than it actually was. This means congestion is rising faster, and thus creates a greater claim on the public weal than if congestion were always with us at roughly the same level.

Time and the City

We sometimes think of the city as a collection of objects in space that exist for the purpose of reducing the costs of human interaction. The city is also a collection of objects in time. Taking the long view, cities once did not exist (the time before the founding of the city), and eventually may not exist again. The list of abandoned cities is long, and will eventually, though this may sadden us, grow longer.
However the city also operates at shorter timeframes. There is the multi-decade cycle of infrastructure renewal and replacement. There is the multi-year (though random) cycle of sports team victories. There is the annual cycle of the city operating through the seasons, with winter and spring and summer and fall events. There is the daily cycle of flows of people into and out of the city.
Why do we see diurnal patterns of flows? Why is there a morning and afternoon peak, or rush hour? The answer is to ensure some set of people (peak commuters) are generally in the same place at the same time. And we do this to reduce inter-personal coordination costs. If we are generally in the same place, we don’t need to pre-arrange meetings, we run into each other in the hallways, I can easily knock on your door, I see you on the sidewalk. Our temporal coordination costs drop. And even if we do need to pre-arrange, it is relatively simple. As I tell my students in class: “I am here because you are here, you are here because I am here.” In contrast, if we are not generally in the same place, we do need to pre-arrange meetings, I will not randomly run into you. Our temporal coordination costs rise.
There are lots of people for whom the congestion costs of the peak outweigh benefits of organizing work on the “standard” schedule. Many people with shifts in workplaces that operate more than 8 hours a day (medical, police and fire, manufacturing, transportation, retail, some construction, media) travel in the off-peak. For some this is necessary (you don’t want to change bus drivers in the middle of the peak), for others convenience (why travel at rush hour when it is unnecessary).
In the Central Time Zone, that peaking pattern is partially dictated by what happens on the East coast. People here go to work earlier than they otherwise would to ensure a greater overlap in time at work with those back East. Similarly, people involved in international trade may keep odd hours locally to coordinate with their customers or clients elsewhere in the world. In other parts of the world, schedules similarly adapt to the needs of trade, as well as local custom. In some places, work lasts until very late, but there are mid-day breaks.
This temporal coordination imposes the cost of increased loads on the transportation system, as people converge and diverge at the same time, requiring either more capacity or more crowding (and slower speeds). We could (and do) smooth the flows on transportation systems, encouraging peak spreading (some of which the market does by itself) through differentiated prices.
We can be spatially coordinated to reduce our scheduling costs, or we can be temporally coordinated so that we have lower space costs. The classic multi-purpose room in 1960s era Elementary schools, hot-desking, or shared parking between office, stadiums, retail, and churches are examples of a form of temporal coordination to share a scarce resource to reduce land and structure costs. Most temporal coordination though shares the scarce resource of the humans being on the same task at the same time, and thus requires more space. Typical cities provide both spatial and temporal coordination, putting people close together and having them do the same things at the same time.
Cities work to reduce temporal coordination costs, one of the many ways they enhance economies of agglomeration. But they do so by increasing spatial coordination costs. We cannot occupy the same latitude and longitude at the same time. If we want to do so, we must go vertical. This adds to the cost of construction. We do not have freedom to use our land any way we want to, we must share some rights to it, because society demands it. This diminishes our freedom of action.

Elements of Access: Transport Planning for Engineers, Transport Engineering for Planners. By David M. Levinson, Wes Marshall, Kay Axhausen.

One expects that improved information and communication technologies will reduce the need for in-person interaction, and we certainly see some of that. But reducing the call of the city does not eliminate it. So long as some physical interaction is required, cities of a form will emerge. The need for young men and young women of different genetic lines to somehow interact in person is one such call upon the pattern of the city.
Just as 200 years ago, the city was barely what it is today, 200 years from now, the city may differ again. Cities may return to being seasonal, like the classic Medieval trade fair. These once comprised entirely temporary structures, which gradually became permanent. Look at the Minnesota State Fairgrounds for a more recent example of the temporary becoming “permanent”. Today we construct state fairs with permanent buildings, but world’s fairs, which do not repeat annually, have temporary structures. While not made of paper mach´e, the buildings of Chicago’s White City or even New York’s 1963 World’s Fair are largely gone. But the world’s fair is a lot less significant than it once was.
If people lose their need for daily interaction, we should expect a thinning of the urban support system, less reliance on costly permanent infrastructure, and more reliance on the ad hoc. Humans will still require shelter, and those shelters may still cluster so long as transport still has costs, but we can easily imagine a world where advanced technology means we don’t need to commute or shop more than weekly. And that means we don’t need to live as close together. And with advanced driverless cars, even that burden (the need to focus on the task of driving) is lifted, enabling even more spread.