Self-study
After the rush-hour speed limit on the British M25 motorway was lowered from 70 miles per hour (115 kilometers per hour) to 50 miles per hour (80 kilometers per hour), rush-hour travel times decreased by approximately 15 percent.
"Surprising" Phenomenon
Why did rush-hour travel times decrease after the rush-hour speed limit on the British M25 motorway was lowered?
Objective
The correct answer will be a hypothesis that explains a key difference between traveling on the British M25 motorway during rush-hour at a lower speed and traveling at a higher speed. That difference must result in shorter travel time when traveling at a lower speed.
12.
Which one of the following, ██ █████ ████ █████ ██ ███████ ███ ████████ ██ ██████ █████ █████████ ██████
a
After the decrease ██ ███ █████████ █████ ██████ ███ ███████ █████ ██ ███ ███ ███ █████████████ █████ ██████ ████ █████ ████ ██ █████ █████ ██ ███ ████
We aren’t concerned with whether average speed is lower at rush-hour than at other times of day. We’re only concerned with rush-hour travel times and why those times decreased even though the speed limit also decreased.
b
Travel times during ███████ █████ ████ ████ █████ ████ ███████████ █████████ █████ ███ █████████ █████ █████ ███ ████████
Like (A), we are only concerned with rush-hour travel times and why those travel times increased after the rush-hour speed limit was lowered. Also, it shouldn’t be surprising that the change in rush-hour speed limit did not affect travel times during periods other than rush-hour.
c
Before the rush-hour █████ █████ ███ ████████ █████████ █████████ ████ ██████ ███████ ██████ ████ ███████ ███ ████ ██ █████ █████████ ████ ██████ ██ ██████████ ████████
This explains the key difference between driving on the M25 during rush-hour at a lower speed versus a higher speed. Driving faster led to more accidents, which caused longer travel times. When the speed limit was lowered, there were fewer accidents and shorter travel times.
d
Enforcement of speed ██████ ██ ███ ███ ███ █████ ████████ ████ ██████ ███ █████ ███ █████████ █████ █████ ███ ████████
The fact that the speed limit was rigorously enforced both before and after it was lowered only shows us that people probably drove at the correct speed, whether 50 mph or 70 mph. The question still remains: why did travel times decrease after the speed limit was lowered?
e
The number of ██████ ███ █████ ██ ███ ███ ██████ ████ █████ ███ ███ ████████ █████ ███ █████████ █████ █████ ███ ████████
This could simply mean that the number of people on the M25 stayed the same before and after the rush-hour speed limit was lowered. Thus, it doesn’t help to explain why travel times decreased after the speed limit was lowered.