A "string diagram" is helpful for planning the traffic flow on a model railroad. Here is mine. Times are shown along the bottom; the diagram covers 5:00am until 8:00pm. Station names appear on the left.

This diagram is a bit unusual because it includes the junctions at Rich Creek and Pepper, and the stations for both legs at each junction are intermixed. The third subdivision station names are red, while the fifth and sixth subdivision stations are blue.

Stations annotated with "REG." are train register stations, where crews must record their train's passage in a register book. An operator is assumed to be on duty at stations with "T.O." and crews must call the Dispatcher and report their train's passage at these stations.

Trains are represented with colored lines. A train's number or name appears near its departure point. Four types of trains are shown; their colors appear in the legend at the bottom of the diagram. Read the diagram from left to right (i.e., as time advances). If a train line flows downward, that is a westbound train. If a train line flows upward, it's eastbound.

A train encounters a station where the train line intersects the horizontal station line. If the train line becomes horizontal, it means that the train stops at that point for the duration of the horizontal line. Some train lines cross station lines that are actually on a different subdivision. An oval at such an intersection indicates that the train doesn't really enter that station, but continues to a station on its own subdivision.

Cutoff times for some trains leaving Glen Lyn are shown as dashed red lines extending to the left of the train lines. These are the times that cars for those trains must be in the yard, to give the yard crew time to make up the trains. Anything arriving in the yard during the time covered by a dashed red line waits until the next available train.

Here are some of the things we can learn from this string diagram: