train kilometre density

例句：

1. 1. The train's speedis directly related to the train kilometerdensity.
   火车的速度与火车公里密度直接相关。
2. 2. The train kilometer density affects thecost of transportation.
   火车公里密度影响运输成本。
3. 3. The train kilometer density is acrucial factor in determining the efficiency of therailway system.
   火车公里密度是决定铁路系统效率的关键因素。