Automobiles VS Public Transport Public transport plays a central role in any efficient urban transport system in developing countries, where at least 16 cities are expected to have more than 12 million people each by the end of this decade, failing to give priority to public transport would be disastrous. The term 'public transport' covers many different types of vehicles, but most commonly refers to buses and trains. Rail services fall into four major categories: rapid rail (also called the underground, tube, metro, or subway), which operates on exclusive rights-of-way (优先行驶权) in tunnels or on elevated tracks trams, which move with other traffic on regular streets light rail, which is a quieter, more modern version of trams that can run either on exclusive rights-of-way or with other traffic: and suburban or regional trains, which connect a city with surrounding areas. The recent trend in many cities is toward light rail over 'heavy' rapid-rail systems. Whereas metros require exclusive rights-of-way, which often means building costly elevated or underground lines and stations, light rail can be built on regular city streets. The concept of public transport also includes organized car pools, in which several people share the cost of riding together in the same private automobile. For US commuters in areas with inadequate bus and train services, this is the only 'public' transport option. But even where other systems are comprehensive, there is vast potential for car pooling recent research shows that in cities the world over, private cars during commuting hours on average carry just 1.2 1.3 persons per vehicle. Public transport modes vary in fuel use and emissions and in the space they require, but if carrying reasonable numbers of passengers, they all perform. better than single-occupant private cars on each of these counts. Although energy requirements vary according to the size and design of the vehicle and how many people are on board, buses and trains require far less fuel per passenger for each kilometer of travel. In the United States, for example, a light-rail vehicle needs an estimated 640 BTUs (British Thermal Units, measure of energy consumed) of energy per passenger per kilometer a city bus would use some 690 BTUs per passenger-kilometer and a car pool with four occupants 1,140 BTUs. A single-occupant automobile, by contrast, consumes nearly 4,580 BTUs per passenger-kilometer. The pollution savings from public transport are even more dramatic. Since both rapid and light rail have electric engines, pollution is measured not from the motor exhaust, but from the power plant generating electricity, which is usually located outside the city, where air quality problems are less serious. For typical U.S. commuter routes, rapid rail emits 30 grams of nitrogen oxides for every 100 kilometers each rail passenger travels, compared with 43 grams for light rail, 95 grams for transit buses, and 128 grams for single-occupant automobiles. Public transport's potential for reducing hydrocarbon (碳氢化合物)and carbon monoxide(一氧化碳)emissions is even greater. Although diesel buses—especially in developing countries—can be heavy polluters, existing technologies, such as filters, can control their exhaust. Buses can also run on less polluting fuels such as propane (丙烷, used in parts of Europe) and natural gas (used in Brazil and China). Test buses in the Netherlands that run on natural gas are estimated to emit 90 percent less nitrogen oxide and 25 percent less carbon monoxide than diesel engines do. In addition to reducing fuel consumption and pollution, public transport saves valuable city space. Buses and trains carry more people in each vehicle and, if they operate on their own rights-of-way, can safely run at much higher speeds. In other words, they not only take up less space but also occupy it for