From: Ruby Quiz <james@...>
Date: 2007-11-09T22:07:07+09:00
Subject: [QUIZ] Vehicle Counters (#146)

The three rules of Ruby Quiz:

1.  Please do not post any solutions or spoiler discussion for this quiz until
48 hours have passed from the time on this message.

2.  Support Ruby Quiz by submitting ideas as often as you can:

http://www.rubyquiz.com/

3.  Enjoy!

Suggestion:  A [QUIZ] in the subject of emails about the problem helps everyone
on Ruby Talk follow the discussion.  Please reply to the original quiz message,
if you can.

-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=

by Gavin Kistner

You have been hired to work for a small city government. The city recently
bought a vehicle counter, one of those kinds that uses pneumatic rubber hoses
stretched across the road. The company that sells the machine also sells
software to interpret the raw data. However, the city has asked you to see if
you can interpret it instead, saving them some money.

The data from the machine looks like this:

	A268981
	A269123
	A604957
	B604960
	A605128
	B605132
	A1089807
	B1089810
	A1089948
	B1089951

The numbers are the number of milliseconds since midnight when the mark
occurred. Thus, the first line above represents a pair of tires driving by at
12:04:28am. The second line represents another pair of tires going by 142ms
later (almost certainly the 2nd axle of the car).

The vehicle counter has two tubes - one stretches across both lanes of traffic,
and one goes just across traffic in one direction. Each hose independently
records when tires drive over it. As such, cars going in one direction (say,
northbound) only record on one sensor (preceded with an 'A'), while cars going
in the direction (say, southbound) are recorded on both sensors. Lines 3-6 above
represent a second car going in the other direction. The first set of tires hit
the 'A' sensor at 12:10:04am, and then hit the 'B' sensor 3ms later. The second
set of tires then hit the 'A' sensor 171ms later, and then the 'B' sensor 4ms
later.

The machine was left to run for 5 days in a row (starting on a Monday). This is
obvious because the times in the data make several sudden drops:

	A86328771
	B86328774
	A86328899
	B86328902
	A582668
	B582671
	A582787
	B582789

The city has asked you to see how many analysis features you can provide from
what the manufacturer's software offers:

	* Total vehicle counts in each direction: morning versus evening,
	  per hour, per half hour, per 20 minutes, and per 15 minutes.
	* The above counts can be displayed for each day of the session,
	  or you can see averages across all the days.
	* Peak volume times.
	* The (rough) speed distribution of traffic.
	* Rough distance between cars during various periods.

Luckily for you, you know that:

	* The speed limit on the road where this is recorded is 40mph
	  (that doesn't mean that everyone drives this speed, or that
	  no one exceeds it, but it's a good starting point).
	* The average wheelbase of cars in the city is around 100 inches
	  between axles.
	* Only 2-axle vehicles were allowed on this road during the
	  recording sessions.

The full data can be found at:

	http://rubyquiz.com/vehicle_counter.data.gz