1. Part (a)
Total # of cars turning left = L(t) dt 18
= 1,658 cars

2. Part (b)
NOTE: I originally got an answer of cars/hour by rounding to 3 decimal places mid-way through the problem. Would this be acceptable to the AP graders? NO. To be safe, wait until the end to round anything off.
L(t) > 150 on the interval (12.428, ). The average value of L over this interval is…
L(t) dt
12.428
16.122 1
cars/hour =

3. Part (c)
200, = 400
This means that the signal will be required if, during any 2-hour time interval,
L(t) dt
The graphing calculator shows us that L(t) has a maximum value at t = hours.
Since this is greater than 400, the intersection WILL be eligible for a traffic signal.
Centering around this max gives us a 2-hour interval from to hours.
L(t) dt =
13.294
15.294