Red Light Cameras
To combat red-light-running crashes, many states are installing
red light cameras at dangerous intersections. These cameras
photograph the license plates of vehicles that run red lights and
automatically issue tickets. How effective are these photo
enforcement programs? The Virginia Department of Transportation
(VDOT) conducted a comprehensive study of its newly adopted program
and published the results in a 2012 study. In one portion of the
study, VDOT provided crash data both before and after installation
of the cameras at several intersections. The data, measured as the
crash rate caused by red light running per intersection per year,
for 13 randomly selected intersections in Fairfax County are given
in the data file called “Red Light Cameras.†At the 0.10
significance level, test the claim that the installation of the
cameras decreased the mean number of crashes at intersections where
the cameras were installed.
Intersection:
1
2
3
4
5
6
7
8
9
10
11
12
13
Before Camera:
3.6
0.27
0.29
4.55
3.09
2.29
2.4
1.09
3.15
3.21
1.88
1.35
7.35
After Camera:
1.87
0
0
1.79
2.04
3.14
2.72
0.24
1.57
0.43
0.28
1.09
4.92
a) Conduct a full hypothesis test by following the steps below.
Enter an answer for each of these steps in your document.
i) State the null and alternative hypotheses using correct
notation.
ii) State the significance level for this problem.
iii) Calculate the test statistic “by-hand.†Show the work
necessary to obtain the value by typing your work and provide the
resulting test statistic.
iv) Calculate the p-value.
v) State whether you reject or do not reject the null hypothesis
and your reason for your answer in one sentence.
vi) State your conclusion in context of the problem (i.e.
interpret your results and/or answer the question being posed) in
one or two complete sentences.
b) Construct a 90% confidence interval using the above data.
Please do this “by hand†using the formula and showing your work
(please type your work, no images accepted here).
