The word it in the passage refers to

Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the questions from 37 to 43
Today, there are 600 million cars in the world. They may seem like a lot. However, there are over 7 million people on our planet. Most of the world's population uses public transportation to get around. The number of people using public transportation continues to rise. Subway systems worldwide carry 155 million passengers each day. That's more than 30 times the number carried by all the world's airplanes. Every day in Tokyo passengers take more than 40 million rides on public transportation.
Yet many people see public transportation as “a depressing experience”, says author Taras Gresco. They say it is slow, crowded, or too expensive. In fact, Gresco says, it is actually 'faster, more comfortable and cheaper than driving a car. Like millions of people, Taras Gresco is a 'straphanger’- a person who rides public transportation. In his book straphanger: Saving Our Cities and Ourselves from the Automobile, Gresco describe the benefits of public transportation. Firstly, it is better for the environment. When people use public transportation, they use less fuel. Twenty people on one bus use much less fuel than 20 people in 20 cars. Fewer cars mean less pollution and cleaner air. Using public transportation can be good for your health in other ways. It can even help you lose weight. In one study, a group of people took public transportation every day for six months. Each day they walked to a bus stop or train station. In six months, each person lost an average of six pounds - almost three kilograms. Taking public transportation has another benefit, says Gresco. It helps people become part of their community. When you are alone in your car, you don't talk to anyone. One Tokyo straphanger told Gresco, “To use public transport is to know how to cooperate with other people,' It teaches you how to behave in a public space’. So, public transportation is more than a way to get to work or school. It can help lead to cleaner cities. It may also lead to a healthier and more cooperative world population.