passenger-kilometer

例句：

1. 1. The train travels 500 kilometers between the two cities.
   火车在两个城市之间旅行了500公里。
2. 2. The distance between the two cities is about 300 kilometers.
   两个城市之间的距离大约是300公里。
3. 3. The bus takes about 2 hours to cover this distance.
   这趟公交车行驶这段距离需要大约2个小时。