I read a lot of forums and articles about transport policy where most of the people agree with each other. The splintering of discussion into groups that agree is a common and well-understood phenomenon that is amplified on the internet.
As well as getting excited by optimal stop spacing, one thing people in these circles agree on is that roads are bad. The most common argument made against roads goes like this:
“Essentially, if you widen roads to reduce congestion, people who were avoiding the road because of congestion will find it more convenient and take more trips, thus increasing traffic again.
So what do you have then? A big expensive project to eliminate traffic, and more traffic.” Streetsblog
“New roads will create new drivers, resulting in the intensity of traffic staying the same.
Mann explains how this counterintuitive reality can possibly be true: “As it turns out, we humans love moving around. And if you expand people’s ability to travel, they will do it more, living farther away from where they work and therefore being forced to drive into town. Making driving easier also means that people take more trips in the car than they otherwise would.” Planetizen
“Research indicates that generated traffic often fills a significant portion of capacity added to congested urban road. Generated traffic has three implications for transport planning. First, it reduces the congestion reduction benefits of road capacity expansion. Second, it increases many external costs. Third, it provides relatively small user benefits because it consists of vehicle travel that consumers are most willing to forego when their costs increase.” Victoria Transport Policy Institute
While I support many of the ideas this argument is rolled out to support, I find the argument itself utterly unconvincing. If you want to argue against investing in roads, you’ll need a better argument. Here’s why.
1. Public Transport will behave exactly the same.
If you widen a road, it will encourage more people to drive on it, bringing congestion to an equilibrium level* on that road, and spilling congestion into other parts of the network.
Likewise, if you increase the frequency with which a public transport service runs, it will attract more people to ride on it, bringing congestion to an equilibrium level and spilling congestion into other parts of the network.
This means that induced demand operates as an argument not to invest in any popular/crowded transport where crowding levels may be deterring travel. I’m not sure that’s what proponents of the induced demand argument intend.
*The equilibrium level is not necessarily the same amount of congestion as before, it’s the level where congestion deters travel.
2. Induced demand is good.
Induced demand means previously people had latent demand for travel, but they were unable to satisfy it. Now they are able to access jobs, get to shops that sell items that match their needs better, visit friends and family more. Any argument about transport investment that objects to people doing more travel should be treated with suspicion, if not contempt.
3. Focusing on congestion is the wrong way to look at transport policy.
If your approach to solving a city’s transport problem is to seek out choke points and jams and try to untangle them, you may end up fighting unwinnable battles against geometric problems. You will become frustrated, growing ever more sure that transport is a zero sum game with no easy answers.
Forget congestion. If you make your yardstick access, you focus on what people want: What places can I get to?
A rational approach to transport planning in a city would be to measure access: From each address, a sum of all the jobs, services and other addresses that can be accessed, averaged across a time period encompassing peak and off-peak.
That number would be aggregated across the entire city to create a total score. Then, you would provide incentives for bureaucrats to improve that number. These bureaucrats must have more than just transport levers at their disposal.
They should also be able to make decisions on zoning and land-use, and road pricing. Improving access can as easily mean moving jobs to people as people to jobs. If a particular investment is expected to have spill over effects that worsen transport times in a far-flung part of the network, the access measure should pick this up and permit that effect to be compared to its positive local effect.
Build a new school, access improves. Add traffic light priority for buses, access improves for some at the expense of others. Price a road, access improves for high-value trips at the expense of lower value trips. Add a new lane on a freeway, access improves locally and probably diminishes elsewhere.
Focusing on access allows trade-offs and comparisons to be made. But often, improved access will involve turning latent demand for travel into real trips. We shouldn’t object too loudly to that.