Highway Robbery: How Induced Traffic makes highway expansion for congestion relief fruitless

Happy New Year to all. No better time to roll out the long-promised post on the induced traffic principle than the first entry of 2012.

I have said often in this blog that we will never win the congestion battle using the methods currently employed. Such methods are the obvious, highway building and expansion, but even the not obvious like light rail or streetcar investments because they don't fundamentally change the system.

The reason that the congestion battle can never be won using the tactics we are is the fact that unlike other parts of our lives, car travel is based on human behavior, rather than a linear supply-and-demand function. When roads or freeways are designed, they are built to accommodate a certain number of cars. Prior decades saw the road building and expansions as an opportunity to meet current and future "demand" for travel. Nowadays, right-of-way is more likely to determine the capacity of the corridor, since most professionals know that the roadways will fill up once they are opened. The professionals planners and engineers recognize the human behavior function makes any other formula obsolete. Sadly, we are still on the current pace because elected officials and, perhaps most important, the public are largely ignorant of this. This is very similar to my transit convenience point. People will do what is convenient. When we build for the car, the car becomes convenient and we have to work within that system.

Here's the gist of the Induced Traffic Principle. As a whole, human tolerance in traffic is for no slower than stop-and-go. Above that speed, they will take that route. They may grumble, complain and mope, but they will still drive in that corridor. Below that speed, drivers will seek alternatives until stop-and-go traffic is resumed. The alternatives are numerous, but the three main ones are seeking alternate routes, such as an artery or rail line instead of a freeway, driving at different times, going to work at 7 instead of 8 in the morning, or not making the trip at all, waiting some other day to go out.

We can all relate to this at some level. Here are some personal anecdotes from me.

1) When I worked in the radio industry, I had to cover an SMU basketball game. I lived in Irving at the time. Instead of taking the freeway into downtown and then Central up, I took Mockingbird instead. Were the freeway running smoother, I would not have driven that route.

2) My family participates in dog shows and when I was a kid, there was a show in San Antonio. I asked why we had to get up so early to get there and my Dad said he didn't want to drive San Antonio's freeway's during rush hour. So we made the trip earlier.

3) Shortly after college, my friend moved to Far North Dallas. I was still in Arlington. When he asked me to come over one day, I said no. I didn't want to have to fight traffic, as that area has the worst traffic in the region. I just didn't make that trip.

Now take these examples and multiply that across the millions of drivers in the area and the scope comes into play. We all have them. Feel free to list your own examples in the comments section.

Taking this behavior and applying it to congestion relief programs that rely almost exclusively on increased capacity illustrates the futile attempt of actual congestion relief. As I noted in this post a few weeks ago, when capacity is increased, the stop-and-go traffic level is raised to higher speeds. This in turn will add people immediately to the new road. People who took alternate routes will go back to this one. Folks who started the trip an hour later will take to the route and folks who elected to not make a trip will.

A planner friend who understands the point was playing devil's advocate one day and said "aren't those good things? If people switch from an old road, doesn't that reduce the congestion there? If people switch times, doesn't that reduce congestion before and after? If people are making the trip they weren't before, isn't that good for the local economy?" The short answer is yes.

However, when you look further it reveals short-term benefits at best. If congestion is reduced on the old route, it too is subject to induced traffic and will soon find others to take its place, most likely those that weren't making trips at all. Once long term effects of freeway building/expansion are added, that reduction in congestion times before and after rush hour will expand again. And the economical argument is flawed because people are going to spend their disposable income one way or another.

The long-term effects that absolutely negate any congestion relief are perhaps more damning than the short-term. Because the short-term is based on human behavior, it would be easily remedied. The long term effects are harder since the built environment directly effects that behavior and is a bit more permanent.

Consider the following timeline. Central Expressway in Dallas was built shortly after WWII, originally conceived as a direct route for the Park Cities suburbs to get to downtown. This let Highland Park and then University Park (now considered close-in neighborhoods) to build out. In the '60's and 70's North Dallas and Richardson grew out. LBJ freeway was built in the '70's. This allowed Plano to reach explosive growth in the '80's and '90's. During the '90's, Central was expanded from a two-three lanes to three-four lanes. In turn, Allen and McKinney saw explosive growth in the late '90's and '00's.

This example repeats itself all over the region and country. Heading west, the Dallas North Tollway expansions heralded the rise of Addison, Plano and Frisco. I-35E saw Lewisville, Denton and the Lake cities rise as it was built out. Irving needed Tx-183 and 114 before its neighborhoods grew. Arlington and Grand Prairie grew when I-30 and I-20 reached their areas. In any direction there are freeways and suburbs that grew out of them, with the freeways as the catalyst for that growth.

While growth in and of itself is not a bad thing, the issue from a congestion relief standpoint is that the growth took the form of auto-oriented developments. Downtown's across the country flourished in the streetcar era primarily because they had a land use and transportation system that matched. When shoppers needed something, they went downtown, to the smaller stores got what they needed, perhaps browsed and went home the same way. In most situations, neighborhood needs were within walking distance.

However, in today's time, numerous trips for small items are not convenient, which paved the way to the big box retailer. Few people enjoy getting in a car, stopping to get a home improvement item, get back in the car, stopping for a new pair of shoes, back in the car, stopping for medication at the pharmacy, drive the car away, getting dinner at a grocer, and stepping back into the car and going home (just typing that felt mundane). That's where the idea of one-stop shopping came into vogue. Now, in our car-based society, anything else seems odd.

The point is that congestion-relief, on the rare occasions it actually occurs, is temporary at best and non-existent at-worst. As long as the big-box retailers build massive parking lots next to the new freeways and cities encourage these in their zoning codes, more trips are a certainty. When that happens, we are back to square one, only with more lanes of clogged roadway.

Unless the transportation system is radically changed, which there seems to be no indication it will, congestion is never going to be relieved, and reduction is unlikely.

While I have hope that Intelligent Transportation Systems (ITS) will help, I don't believe they will solve the problem. They can be effective since they persuade human behavior. Congestion charges a la San Francisco are ITS examples. Tollroads, which aren't popular, are too. Even HOV lanes are further case studies. But my concern is that as long as the country's transportation system is so skewed towards auto travel, they will never be the magic bullet some propose. Here's hoping I'm wrong, but I see the only solution involves taking people out of their cars while simultaneously making other trips shorter. They only way that happens is through whole scale land use changes, which aren't likely to happen on a scale large enough as long as congestion relief is primarily attempted through capacity increases.