困难主要是在基站（或者发射塔）与用户之间缺乏直达线路。

The difficulty is primarily due to the lack of line of site between base stations, or towers, and the subscriber.

youdao

旧线路上的班次可能要增添停靠站；乘客可能被迫要乘坐非直达的路线。

Trains on the old line might make more stops; passengers might be forced to take indirect routes.

youdao

这一升降机可以通过在楼层间货升降层之间的运输线路或机械进行露台和夹楼的直达运输。

These package lifts provide nonstop transportation to or from balconies and mezzanines, over aisles or machinery, between floors or conveyor levels.

youdao