There's a mile-long or km-long, depending upon which consist you decide to make up out of some wagons by wilem2 . Then there are mile-post assets, which you then plop down at the end of the consist.
Measuring Wagon Imperial 52'8 Green,<kuid2:97008:60821:2>
Measuring Wagon Imperial 52'8 Pink,<kuid2:97008:60822:2>
Measuring Wagon Imperial 52'8 Red,<kuid2:97008:60823:2>
Measuring Wagon Imperial 52'8 Yellow,<kuid2:97008:60824:2>
Measuring Wagon Metric 25m Green,<kuid2:97008:60811:2>
Measuring Wagon Metric 25m Orange,<kuid2:97008:60812:2>
Measuring Wagon Metric 25m Red,<kuid2:97008:60814:2>
Measuring Wagon Metric 25m Yellow,<kuid2:97008:60813:2>
There's no faster way to do this that I can think of, unfortunately.