历史上的趋势 用铁路进行运输的质量是无容置疑的，甚至于其竞争的对手也都承认：铁路节省空间的占用，还节省是因为耗能少，因为普遍使用电能因此少污染，很少产生温室效应的气体． 实际上，要是只考虑二氧化碳的排放，每ｔｋｍ（吨·千米）铁路货运的平均碳含量以ｇ表示就是 Historical trends The quality of transport by rail is undisputed, and even its competitors are acknowledging that the space-saving use of railways also saves because of less energy consumption, less pollution due to widespread use of electricity, and less Greenhouse gas. In fact, if we only consider the emission of carbon dioxide, the average carbon content of railway freight per tkm (ton · km) is expressed as g