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Sunday
Aug032014

Analysis of Spikes in Red Light Camera Tickets

The city has acknowledged the Tribune's analysis and is now reviewing over 9,000 tickets.  There are other stories that say this number will climb as high as 16,000 tickets.  The city has also stated they will more carefully monitor their RLC contractor and post the ticket violations daily for each intersection.  This transparency would aid in ensuring the integrity of the red light camera tickets.

I decided to do my own analysis of the camera spikes.  I used a statistical technique that looks for outliers in a time series.  I ran this on both a daily summation and a weekly summation of the tickets.  The results were revealing: 

  • Over 100 intersections had a spike  
  • At least 20,000 to 40,000 tickets are affected by the spikes
  • Spikes are largely pre-2010.  I found that 2007 and 2008 accounted for 68% of all the spikes.  By 2010, the amount of spikes dropped considerably.  This suggests that whatever the cause of the spikes was, it was largely corrected several years ago.
  • Unlike the Tribune, a spike was not found at Western and Touhy

I have attached to this post, a complete spreadsheet with the results.  

Some caveats:  

 

  • The analysis looks for spikes, this means values that are outside the normal range.  I tried to filter out the low spikes, but if the number of tickets is too low, that is also considered a spike.  
  •  I ran the analysis on both a weekly and daily basis.  At some intersections, the pattern of traffic would result in spikes on a weekly basis, because Saturday could be the busiest travel day.  I did try to control for this (as well as seasonal changes), but you may see this.  
  • The dates provided are approximate with a few days of the spike.
  • UPDATE 8/8/2014 - A small amount of the spikes were the initial values, I updated the analysis to remove those spikes

 

So go find some spikes!  Take a look at the data, see my RLC site, and analyze using a daily or weekly period.  You can adjust the date range to zoom in on specific dates.

Let me know what you find

Reader Comments (1)

I think one piece of data that would give us more context for the cause of the spikes is the population of vehicles at each intersection on a daily basis. We have the sample (those vehicles that received red light camera tickets) but we don't know how many vehicles could have possibly gotten a red light camera ticket – eligible or ineligible for a violation – because of their presence.

August 4, 2014 | Unregistered CommenterSteven Vance

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