At streets.mn, Andrew Owen has a fascinating look at the work he has done with David Levinson on measuring accessibility in the Minneapolis-St. Paul metro area. I’ll let Andrew define accessibility:
Accessibility measures the ease of reaching valued destinations.
Think about the last trip you made. You were in place A, you wanted to be in place B, and you got there by paying some sort of cost. There are several components at work here.
First, lets look at your reason for wanted to be in place B. That’s the whole reason the trip took place! You didn’t just want to move around for a bit, and then come back to A. (People do that sometimes, but we don’t consider it travel — we call it things like recreation, exercise, or NASCAR.) No, you had a reason for traveling to place B. That reason, from a transportation economics perspective, is the value that place B holds for you.
Now that we’ve established that place B has some value to you, it would be great if you could get there whenever you want, for free. But you can’t. Even if you frugally decide to walk from A to B instead of drive, fly, take the bus, or ride a horse, you cannot escape spending a precious resource: your time. The total amount of resources you spend in getting to B, whether they are time, money, oats (for your horse), or some combination, is thecost you pay to reach place B. To generalize just a little bit more, we can say that when the cost of getting to B is low, then B is easy to reach.
That, in a nutshell, is accessibility. It combines the value that we get from travel with the cost of making the trip. I love accessibility because it neatly encapsulates what I consider to be the fundamental purpose of transportation systems: providing ways for people to get to places they want to reach, at costs they are willing to pay.
Andrew then goes on to discuss the results of a project they completed for MN-DOT on measuring “cumulative opportunities accessibility”, or how many things can be reached within a given cost (time) threshold by car and transit. You should read the whole post to see Andrew’s many interesting conclusions.
After reading it, a few things jumped out at me:
Owning a car gives you an overwhelming advantage in accessing jobs in this metro. In a huge swath of the metro, making up all but the most outlying areas, you can access at least 100,000 jobs in 20 minutes by car. A very large area, incorporating both core cities and most first-ring suburbs, can access over 500,000 jobs and up to 2.2 million. By contrast, transit accessibility to jobs maxes out at 100k – 250k jobs, and this is if you live very near downtown Minneapolis. If you live in parts of North and South Minneapolis and use transit, you have the same access to jobs in 20 minutes as someone with a car living in southern Dakota County (like in a corn field). Or, based on the map shown below, from parts of Minneapolis, you can only reach 10-20% of the number of jobs reachable by car.
Is our transportation/land use system is failing those that can least afford a car? I’d say that judgment wouldn’t be a stretch looking at these maps. It will be interesting to see what MNDOT does with this information.
There will be a temptation to interpret this metric as only about transportation. It’s actually about destination density AND transportation system performance. I posted this idea in the comments and Andrew had a good response:
That’s a great point, and I didn’t talk much about the land use side of things in this post.
I feel like the popular conception often sees land use as more static than transportation; it is the background canvas upon which the dynamic lines of transportation are drawn. Discussion of expensive, exciting transportation systems tends to magnify this effect.
But in reality land use is far more dynamic! Transportation systems change in big fits and starts, but land use is constantly evolving in countless small ways. Even if we completely halted new investments in transportation, we could still make huge changes in accessibility through the policies we choose to guide land use development.
MNDOT mostly builds roads, so I assume they’ll use this report to think about where and how they should build more roads. But if your goal is increasing accessibility, is it cheaper to lay blacktop or increase jobs/housing density? What are the environmental implications of choosing each of those options? Why do we have one half of the equation that’s totally socialized (road & transit building) and one that is totally privatized (with obvious regulation – land use controls/building construction)?
What if instead of a Department of Transportation we had a Department of Accessibility and it’s mission was to improve accessibility while meeting environmental standards, building resilient systems, and being economically viable? I bet it would look at lot different than our current DOTs (hint: it would do a lot more with land use).