Final answer:
The best way to increase the efficiency of traveling by car is to increase the number of passengers.
Step-by-step explanation:
The best way to increase the efficiency of traveling by car would be to increase the number of passengers.
This is because the energy expenditure value of traveling by car is 3.6 MJ/passenger-kilometer. By increasing the number of passengers in the car, the energy expenditure per passenger-kilometer will decrease.
Increasing the gas mileage, reducing the number of miles traveled, or using a different energy source may help reduce the overall energy consumption of the car, but to increase the efficiency of traveling by car, increasing the number of passengers is the most effective option.