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Add updates to motorcycle post

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agude committed Feb 20, 2019
1 parent 9ef9033 commit bf38e9a48a9933d55a2b03191f08a5517d879a05
Showing with 44 additions and 43 deletions.
  1. +44 −43 _posts/2017-02-21-switrs_motorcycle_crashes_by_date.md
@@ -27,11 +27,11 @@ better understand what sort of risks that brought.
[lastpost]: {% post_url 2016-12-02-switrs_crashes_by_date %}
[switrs]: http://iswitrs.chp.ca.gov/Reports/jsp/userLogin.jsp

I expected the general trends to match the trends I found when [looking at all
motor vehicles][lastpost]. There I found that commute accidents accounted for
the majority of accidents, and so holidays and weekends that most people have
off result in fewer accidents. Motorcycles, we will see, do not follow these
trends.
I expected the accident trend for motorcycles to match the one I found when
[looking at cars][lastpost].[^1] There I found that commute accidents
accounted for the majority of accidents, and so holidays and weekends that
most people have off result in fewer accidents. Motorcycles, we will see, do
not follow this pattern.

One thing before we get started: the number of riders on a given day (or more
accurately, the [number of miles ridden by them][vmot]) has the most impact on
@@ -66,15 +66,15 @@ AND Motorcycle_Collision == 1 -- Involves a motorcycle
AND Collision_Date <= '2015-12-31' -- 2016 is incomplete
{% endhighlight %}

This gave me 193,336 data points (accidents) to examine spanning 2001 to 2015.
[Just as before][ds], accidents from 2016 are rejected because there is not
yet complete data for the year.
This gave me 193,336 data points (accidents) to examine spanning 2001 through
2015\. [Just as before][ds], accidents from 2016 are rejected because there is
not yet complete data for the year.

[ds]: {% post_url 2016-12-02-switrs_crashes_by_date %}#data-selection

## Accidents per Week

For all motor vehicles, [I found that there was a decrease in accidents][apw]
For cars, [I found that there was a decrease in accidents][apw]
starting in 2008 as people stopped driving to work during the [Great
Recession][gr]; but apart from that trend, I found that the week-to-week rate
changed relatively little, with holidays providing the largest increases and
@@ -92,30 +92,28 @@ trends. However, the trends (plotted below) are completely different.
As expected, there are far fewer accidents because there are far fewer
motorcycles: there are about [27 million vehicles in California, but of those
only 770,000 are motorcycles][dot]. The next observation is that, unlike for
all vehicles, there is a strong seasonal effect---even in sunny California,
motorcycle ridership drops drastically in the winter! And unlike the trend for
all vehicles, there is not a large decrease due to the recession. Finally, I
note that there is an overall upward trend in the number of motorcycle
accidents.
cars, there is a strong seasonal effect---even in sunny California, motorcycle
ridership drops drastically in the winter! And unlike the trend for cars,
there is not a large decrease due to the recession. Finally, I note that there
is an overall upward trend in the number of motorcycle accidents.

[dot]: https://www.fhwa.dot.gov/policyinformation/statistics/2012/mv1.cfm

As I noted above, commute accidents for all vehicles account for the majority
of accidents. However, the data suggest that for accidents involving
motorcycles, commute traffic is not dominant. Moreover, unlike the results for
all vehicles, people keep riding even when out of work; but they also stop
riding when the weather is poor. Next we'll look at accidents by day of the
year instead of by week.
As I noted above, commute accidents for cars account for the majority of
accidents. However, the data suggest that for accidents involving motorcycles,
commute traffic is not dominant. Moreover, unlike the results for cars, people
keep riding even when out of work; but they also stop riding when the weather
is poor. Next we'll look at accidents by day of the year instead of by week.

## Day-by-Day

When looking at all motor-vehicle accidents [I observed that holidays were the
maxima and minima][dbd] in the average number of crashes by day of the year.
On holidays where people have the day off, the number of crashes decreases,
whereas the number increases on holidays where people work and then go out
afterward, like Halloween. Motorcycle accidents do not follow this trend.
Instead, the holidays show quite disparate results: some holidays dip, some spike,
others show almost no deviation from a normal day.
When looking at car accidents [I observed that holidays were the maxima and
minima][dbd] in the average number of crashes by day of the year. On holidays
where people have the day off, the number of crashes decreases, whereas the
number increases on holidays where people work and then go out afterward, like
Halloween. Motorcycle accidents do not follow this trend. Instead, the
holidays show quite disparate results: some holidays dip, some spike, others
show almost no deviation from a normal day.

[dbd]: {% post_url 2016-12-02-switrs_crashes_by_date %}#day-by-day

@@ -141,14 +139,14 @@ but only `n = 3` for leap day.

## Day of the Week

The weekends [showed a decrease in the number of all motor-vehicle
accidents][dotw]. But for motorcycles, for whom weekends are the prime riding
time, there is actually an increase on the weekends. If we think of weekends
as a kind of mini-holiday, they provide a way to look at the same seasonal
holiday phenomenon [discussed above][this_dbd]. Winter holidays showed high
variance, so I would expect to see some weekends with high winter ridership,
and some with low ridership. Summer holidays had low variance, so I expect to
see similar ridership on all summer weekends.
The weekends [showed a decrease in the number of car accidents][dotw]. But for
motorcycles, for whom weekends are the prime riding time, there is actually an
increase on the weekends. If we think of weekends as a kind of mini-holiday,
they provide a way to look at the same seasonal holiday phenomenon [discussed
above][this_dbd]. Winter holidays showed high variance, so I would expect to
see some weekends with high winter ridership, and some with low ridership.
Summer holidays had low variance, so I expect to see similar ridership on all
summer weekends.

[dotw]: {% post_url 2016-12-02-switrs_crashes_by_date %}#day-of-the-week
[this_dbd]: #day-by-day
@@ -178,11 +176,14 @@ weekend results could be due to weather.

## Conclusion

Motorcycle accidents do not follow the same trends as for all motor vehicles.
Motorcyclists continue riding even when they do not have a job. Seasons have
a large effect on the number of riders out on the road. Riders are also out on
holidays in the summer when other vehicles take the day off, and have high
variance for winter holidays and weekends when the weather may turn against
them. There are many more ways to explore motorcycle accidents---time of day,
type of motorcycle, vehicle at fault---but those will have to wait for another
day.
Motorcycle accidents do not follow the same trends as for cars. Motorcyclists
continue riding even when they do not have a job. Seasons have a large effect
on the number of riders out on the road. Riders are also out on holidays in
the summer when other vehicles take the day off, and have high variance for
winter holidays and weekends when the weather may turn against them. There are
many more ways to explore motorcycle accidents---time of day, type of
motorcycle, vehicle at fault---but those will have to wait for another day.

---

[^1]: Not just cars, but motorcycles, bicycles, pedestrians, etc. as well. However, it is mostly "cars" and so for simplicity that's what I'll refer to it as.

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