goodyear2013 wrote:
The faster a car is traveling, the less time the driver has to avoid a potential accident, and if a car does crash, higher speeds increase the risk of a fatality. Between 1995 and 2000, average highway speeds increased significantly in the United States, yet, over that time, there was a drop in the number of car-crash fatalities per highway mile driven by cars.
Which of the following, if true about the United States between 1995 and 2000, most helps to explain why the fatality rate decreased in spite of the increase in average highway speeds?
(A) The average number of passengers per car on highways increased.
(B) There were increases in both the proportion of people who wore seat belts and the proportion of cars that were equipped with airbags as safety devices.
(C) The increase in average highway speeds occurred as legal speed limits were raised on one highway after another.
(D) The average mileage driven on highways per car increased.
(E) In most locations on the highways, the density of vehicles on the highway did not decrease, although individual vehicles, on average, made their trips more quickly.
Hi, I chose (E). Can anyone explain why it is not the right choice, please.
OE is not clear to me. Thanks.
Responding to a pm:
Premises:
- Faster a car, more is the risk of fatality.
- In a span of 5 yrs, avg highway speed increased.
- In the same time, number of car-crash fatalities per highway mile driven by cars reduced.
Say, per year, the total number of highway miles driven by all cars is 1000. Say, there are 10 cars and each drives 100 miles every year on the highway.
If there were 10 fatalities, number of car-crash fatalities per highway mile driven by cars = 10/1000 = 0.01
Assuming everything same, if speed of cars increase substantially, expected number of fatalities increases. Say it becomes 20.
So number of car-crash fatalities per highway mile driven by cars = 20/1000 = 0.02
This is what is expected.
Oddly, this number actually went down. (B) tells you that this was because people were more careful and cars were better. So number of fatalities went down. Fair enough.
(D) The average mileage driven on highways per car increased.
Avg mileage driven on highways per car was 100 miles in our previous case.
Say, avg mileage driven on highways per car increases to 200 miles now.
More miles are driven (assuming number of cars is same) but this indicates that number of fatalities will also increase. From 10, we might see 20 fatalities. This option does not imply that number of fatalities will remain the same i.e. at 10.
Or think of it another way - there is a certain number of fatalities per highway mile driven say 0.01. It doesn't matter how many miles were driven exactly. This only implies that if 100 miles were driven, there was one fatality. If 1000 miles were driven, there were 10 fatalities. If 10000 miles were driven, there were 100 fatalities. The fact that people have started driving more does not increase/reduce this number.
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Karishma
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