Friday, September 9, 2011

Bending The Culture Curve

There's been a lot of news since the last post about complete streets and safety at this site.

Traverse City leaders are making traffic safety a priority and released a Bicycle Safety Rules PDF.

Also See IPR: Bike-Car Crashes Concern City Leaders In T.C.

There was a study released on the most dangerous cities for pedestrians in the U.S.
See NYT: On Wide Florida Roads, Running for Dear Life

And the University of Michigan did a study that concluded Michigan traffic accidents have a higher external cost to society than crime.
See DetNews: Traffic crashes cost Michigan $9.1B, more than crime

These reports gave me the impetus to mention something that I neglected in The Mandate Of Complete Streets.

That is Culture. What makes walking part of a culture and why are some areas safer? Is there a culture of safety?

When I think of a walking culture I think of the U.K. Specifically, The Ramblers. Walking is so important to the fabric of English society that the Ramblers ensure that at least once per year every foot path in the U.K. is traveled in order to maintain the public's right-of-way.

Can we have that? How do we make walking safely part of our culture when for the last 50 years the United States has been expanding roadways and making roads safer for vehicles but dangerous by design (Transportation for America PDF report) for everything else? How does the culture buy into the idea that more than vehicles move?

While Complete Streets are a new thing in the U.S., the similar concept of Living Streets has been in England since 1929.

So we could wait 80 years and let the ideas of Complete Streets filter through the culture, or we could use data to drive our decisions.

At my job I analyze data sourced from across Michigan and establish baselines of how many Internet problems per number of devices is normal and then look for areas with abnormal trouble rates and search for ways to lower that baseline rate.

When I read the University of Michigan Transportation Research Institute study: Societal costs of traffic crashes and crime in Michigan: 2011 update, I realized similar data was available in the study's data source: 2009 Transportation Data Center
Data Set Codebook

We had accidents per county and the census can give us population. Perhaps I could apply them?

I found some Michigan web sites with traffic crash data:
-Michigan Traffic Crash Facts
-Michigan State Police Traffic Crash Statistics
-Michigan State Police Traffic Crash Reporting Information

They had the reports I was looking for as PDF's:

-2010 Michigan Traffic Crash Facts for County/Communities


I used the 2010 Census to get population numbers.

I exported the crash data from the PDF's to a spreadsheet.

I then calculated median accident rates per number of people in the community and also plotted these on a graph to look for trends.

I did not expect to see any trends or correlations as there seemed to be so many different variables that can have an effect on traffic accidents. But that is not what I found.


The calculated median accident rate for Michigan in 2010 is 32.2 accidents per 1000 people. And it all fit on a trend line (which surprised me):

Next I uploaded the tables to OpenHeatMap to see if there was any pattern to which counties were above this 32.2 accident rate and which were safer. Green is a lower accident rate and red is a higher accident rate by population.

Link to larger version: Michigan County Accident Rate (You can hover over each county to see its Accident Rate score)

It appears to me that rural counties have a higher rate of accidents when weighted for population.

I then applied the same methods to Bicycle Accidents and Pedestrian Accidents.

The calculated median bicycle accident rate for Michigan in 2010 is 0.13 accidents per 1000 people.

Full size Map: 2010 Michigan Bicycle Accident Rate

The calculated median pedestrian accident rate for Michigan in 2010 is 0.15 accidents per 1000 people.

Full size Map: 2010 Michigan Pedestrian Accident Rate

The Bicycle and Pedestrian Accident rates do not show as strong a correlation as total accidents but there is still a pattern.

When looking at the county maps it appears to me that the counties with a strong biking culture have the highest rate of bicycle accidents. These would be counties hosting large Universities where many students use bikes out of necessity and Grand Traverse County where people choose to ride.

It is harder to make sense of the Pedestrian Accidents map. It could be suburban walkers who don't have access to sidewalks are in greater danger.

To explore this possibility I made a map of the Walk Scores Of Michigan's 65 Most Populous Cities with data from WalkScore:

What you see is that city cores have higher walk scores and the suburbs get progressively worse (clearly evident in Wayne County). But is this related to safety?

At there is a Data Query Tool that lets you build specific maps and tables for defined areas. I used it to look at Traverse City and Grand Traverse County.

2010 Crashes in Grand Traverse County involving pedestrians:

You can see that though many pedestrian accidents were reported within Traverse City proper these usually did not result in injury. But the pedestrian accidents in Grawn, Kingsley, and Williamsburg while fewer in number resulted in serious injury and fatalities.

2010 Crashes in Grand Traverse County involving bicycles:

What I see on this map is more bike accidents downtown, but worse injuries outside of downtown.

What do we do?

Based on these maps and tables I believe that implementing design concepts such as Complete Streets can make roads safer for people, whether they are walking, riding a bike, or driving a car. And I believe that if we make the roads safer for all forms of transportation then more people start using those other forms of transportation. The economy, freed from the burden of unnecessary accidents, grows.

By bending the accident trend lines we can change the arc of our culture.

There are still many questions though and I hope that the research here can serve as a baseline for the future. Two big questions I look forward to having answered are:

-do communities that implement Complete Street designs see their Accident Rate decline?
-do communities with better WalkScores have lower accident rates?

For anyone who wants to do their own research I have uploaded my spreadsheet to Google Docs from there is it easily exportable.