Wednesday, December 03 2014 @ 06:15 AM UTC
Contributed by: B' Spokes
B' Spokes: (Today's tangent in trying to call attention to Maryland's high pedestrian fatality rates from national organizations) Normalizing data is an interesting concept, how do you compare different groups with different characteristics? Especially when talking about road safety. It seems the road folks are obsessed with "exposure" and not the toll traffic fatalities has on the general population. Which to me would be like Baltimore saying since we have a lot of guns on the street (exposure) our gun violence is not that high considering the exposure. Or maybe a better analogy would be to say that since we have more people on the street so someone has a better chance of catching a stray bullet therefore our gun violence is not that bad.
Whether or not we have a gun violence problem is based on deaths per population and I'll assert traffic deaths should do the same and not per Vehicle Miles Traveled nor how many are out walking. More or less traffic is its own kind of problem, mixing that in with fatality rates just obnubilates the underlying problems and thus the solutions. People everywhere do the same things, basically go to work and shop. Traveling farther to do the same things does not improve safety nor the quality of life. So why do we accept this as a fair way to normalize fatality rates for comparisons?
Don't get me wrong, places that have a high pedestrian fatality rate with a low mode share are bad and should be highlighted but on the other extreme, are places with a high pedestrian fatality rate and a high mode share good? It comes down to what are we trying to point out, fatality rates or mode share? As I said, both have their issues and both have their solution sets (with some overlap) but why mix the two up?
A new report from the International Transport Forum finds that the United States had more road deaths per capita in 2012 than Canada, Australia, Japan, and all of the European nations that reported data.
Specifically, the US had 10.7 road deaths per 100,000 people. Canada and France both had 5.8. And the United Kingdom was down at 2.8. (The report explains that the per-person death rate is helpful for comparing deaths from various causes.)
But then it goes on to say that when the comparison is done by Vehicle Miles Traveled the US looks a lot better. Seriously? The fact that we drive a lot more than the rest of western civilization makes us better?
This obsession with exposure even got into Smart Growth America's report Dangerous By Design
. Where their Pedestrian Danger Index (PDI) is modified by pedestrians walking to work mode share. Like a 2% mode share means that pedestrians can be killed at twice the rate to rank the same with a place with a 1% mode share, that is wrong! That's that's taking a 2% change and making it a 200% change. How about normalizing on those who drive to work? More cars (less people walking), more dangerous right? (This would avoid the wild fluctuations where walking is is up to 5 times that of Florida so fatality rates are ranked 5 times better than what they are IMHO.) So the question is, should "exposure" be based on cars that kill or people who walk? (the latter sounds too much like victim blaming to me. Are they really trying to say, "The more people who are out walking naturally the more that are going to get killed." This is the exact opposite of the safety in numbers concept, granted the jury is still out if this is a proven concept but still we cannot assert the opposite across different population characteristics.) Besides Dangerous by Design's methodology makes the New York metro area's high pedestrian fatality rate one of the safest metro areas to walk, this does not feel right to me. The way I would tentatively do the Pedestrian Danger Index by the change in the population that drives, New York's ranking would improve a few notches over a pure pedestrian fatality rate but it still would be high on the list. And for the converse, the Nashville, TN metro area their ranking would be worse by a few notches because so many drive to "justify" their pedestrian fatality rate.
The Dangerous by Design Report takes normalized fatality rates and normalizes them again. So we are normalizing normalized traffic fatalities, something about that just screams of trying to make something bad sound not that bad,
Back to New York Metro area, sure a lot of people in Manhattan walk but think about the Bronx and New York's Vision Zero
. I really don't think New York metro deserves a ranking of 48 (with 51 being the least dangerous metro area for pedestrians.)
The biggest problem with using the primary mode of transportation to work it fails to capture the size of the population that is out there waking. Take kids for example which are not in the mode share numbers, to ball park the error, kids make up ~14% of the population. So adding that to those adults that walk would change the range from 1 - 5 (% of adults that walk) to 15 - 20% (of the population that walks), an increase of a third not the 500% that they are using in their math. And that's just one segment of the population that they fail to capture.
Comparisons of the walking share to work is fine, as it is an indicator
of how walkable one place is compared to another but using it to determine the size of that population and its "exposure, well that's just wrong, Seriously deaths per population per another population number is supposed to be a meaningful number?
My next point is I looked up the time of day pedestrians were killed here in Maryland and topping the list is what I would call bar closing times, next was lunch time. Neither has anything to do with how people get to work so why are we normalizing on that? In fact Pedestrian fatalities during normal commute times were near the bottom of the list. "the per-person death rate is helpful for comparing deaths from various causes"
Life is life everywhere and the rate in which pedestrians die is indicative how safe the streets really are for pedestrians and making bad places look better based on an unproven concept of "exposure" is wrong.
I was biking through Towson during lunch time and there where hoards of people out walking. I am willing to bet over 90% of those drove to work. That is to say how many walking around work centers is not always determined by peoples principle mode on how they got to work in the first place.
My rework of their tables based on pedestrian death rates follows. IMHO excluding this information is wrong. If they want to add tables based on other normalized data fine but I think their math is way off in their current thinking. (Side note: I can understand fatalities per vehicle miles traveled to justify freeways as they eliminated a known danger, intersections. So apply vehicles miles traveled in this instance proves (or disproves) the safety advantages of freeways. But outside of this context diluting fatality rates for a given population with vehicle miles traveled rewards sprawl and penalizes compact development. Exposure (vehicle miles traveled to name one) should not be the universally accepted way to compare diverse populations unless it is part of what we want to test or show. IMHO What the Dangerous by Design Report does is prove that pedestrian "exposure" by those who walk is not a valid way to compare diverse populations )