Sunday, December 11, 2016

NYC vehicular accidents: WHEN?

hen do most vehicular accidents in NYC happen?  

My data source is the NYPD vehicular collision dataset ranging from July 1, 2012 - December 6, 2016.

We would expect most accidents to occur during hours where more people are driving/commuting. Since most people neither work nor go to school on weekends, we would also want to look at weekdays and weekends separately.  Which hours have the most/least accidents?  Do we find any differences between weekends and weekdays?  Are findings consistent across years (2012-2016)?

Below you can see colored bar plots of the yearly percent of vehicular accidents (y-axis) by hour of the day (x-axis).  The hour of the day is expressed such that hour 0 is between 12:00 am to 12:59 am and hour 23 is between 11:00 pm - 11:59 pm . The bar colors range from dark green (least) to dark red (most) to accentuate the variance across the hours of the day.  The top graph shows weekdays, while the bottom shows weekends.

From the results in the bar plots, below are the main findings that are consistent year over year.

  • 2 pm as well as 4-5 pm are when most vehicular accidents occur year over year.
  • There is an 8-9 am spike in accidents on weekends that is not present on weekends.  
  • The hour with the least percent of accidents shifts from 3 am on weekdays to 7 am on weekends.  

What day in the week has the most vehicular accidents?  Is it Friday when people are gearing up for a night out?  Or is it Monday when people are groggy from sleeping in on the weekend and rushing to work?  What day in the week has the least vehicular accidents?  To answer this question, see the horizontal bar plots below illustrating percent of accidents by day of week across years.

From the results in the bar plots, these are the main findings consistent year over year:

  • Friday had the most vehicular accidents 
  • Sunday had the least vehicular accidents 

Note that the findings don't necessarily mean that you are less likely to get in a vehicle collision on Sunday versus Friday, only that the absolute volume of vehicle collisions is lower.