## Archive for **November 17th, 2009**

## Big car, Small car – Which one is safer?

As a new parent, I have always been guilty of driving a compact car when everyone around me keeps telling me that even though SUV’s are bad for the environment they are so much safer in case of an accident. I cringed a bit at every such discussion but thought that maybe they had a point.

But then I thought why not use data visualization to get to the bottom of this and find out what the truth is. Let me preface this by saying that this is my first attempt at visualizing the data I could find for free and any visualization suggestions or data sources that you are aware of will be greatly appreciated.

* [Note: No fancy visualizations here :) Only good old bar graphs]*

**Step 1 – Type of the car vs Fatalities **

I first wanted to find out what is the breakdown of car crashes as compared to the type of car. I found that there is extensive data (see data sources below) about car crashes and fatalities. I decided to use fatalities as a measure of how ‘safe’ the car is and so this graph shows the type of car as compared to the fatalities in 2008. I was sad to see that ‘Passenger cars’ were ranked first but happy to see that ‘Light trucks’ were pretty high up too. Minivans, Compact utility and Large Utility vehicles had far fewer fatalities and I was worrying whether my worst fears (SUV/Minivan = safer) were coming true.

**Step 2 – Sales for each type of car**

But then I thought that the number of accidents obviously is very dependent on the number of cars that get sold per year and if more passenger cars were getting sold, then more of them would be in a fatal accident thus giving it a higher number. So I found out what the car sale numbers were for 2008 (see data source below) and decided to plot that.

**Step 3 – Comparing the Fatalities/Sales ratio**

Then the next obvious thing to do was to compute a ratio of the number of fatal accident per type of car with the number of cars sold for that type in a year. On computing the ratio, I found something very interesting. Sorting the graph based on this ratio, I found that *Compact Utility* vehicles had the highest ratio of fatal accidents to sales. If you look at the first graph, you will see that the compact utility vehicles do not have a large amount of fatal accidents to begin with, but then when that number is divided by the total amount of compact utility vehicles sold, we find an interesting insight (much to my relief and joy).

Passenger cars have a lower ratio than Compact utility vehicles, Large utility vehicles and Light trucks. :)

Anyone who has used Tableau has probably already guessed that all these visualizations were created using Tableau Software and so I visualized the Ratio, Fatal Accidents, Sales all in one image. It shows clearly how compact utility vehicles have a high ratio even though trucks and passenger cars have higher fatalities and more cars of those types were sold.

My current data sources are (Please let me know if you are aware of better ones):

Fatality analysis reporting system – http://www-fars.nhtsa.dot.gov/States/StatesCrashesAndAllVictims.aspx

WSJ – Car sales for the year so far – http://online.wsj.com/mdc/public/page/2_3022-autosales.html