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? ['The increase in average highway speeds occurred as legal speed limits were raised on one highway after another.', 'The average number of passengers per car on highways increased.', '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.', '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.']