Trackside
The shared track
MARC’s Penn Line runs on tracks it shares with faster express trains — and on this corridor those trains have priority. When one is running late and catches up, the local train ahead of it usually gets held aside to let it pass. Trackside can show you this because it watches both fleets on the same track at once, minute by minute — a picture no ordinary train app has.
One day on the corridor
This is every train on the corridor on Aug 6, 2026, northbound (toward Baltimore) — each line is one train, sliding down the page as it moves along the route and to the right as the clock runs. Where a faster express line crosses a local one, that local train was passed — usually held a few minutes near that spot while it happened.
- Local (Penn Line) train
- Faster express train
- A pass — express crosses local
One representative service day, chosen for the most complete tracking. A picture of how the corridor works, not a reliability score.
What eight weeks of tracking showed
Over about eight weeks of continuously recording every train on this stretch, one pattern held up clearly:
- Most passes cost almost nothing. When the faster train is running on time, the corridor has room for it and the local train it passes barely notices. The great majority of passes are routine like this.
- A late pass is the expensive one. When the faster train is already running late as it catches up, the local train it passes tends to lose about five to nine minutes — even when that local train was running on time itself.
- The delay follows the pass. The local train usually starts slowing only after the faster train has closed in behind it — so the pass looks like the cause, not a coincidence that happened to line up with it.
- You can often see it coming. A faster train catching up is visible on this stretch several minutes before it draws alongside, which is the window the app uses to tell you a pass is happening.
- The third track is what makes it possible. It takes a spare track to overtake on; where the corridor narrows to two, nobody passes anyone and the local train simply keeps its place in line.
This is a pattern, not a promise: plenty of late-running passes still cost nothing, and roughly one time in seven it does not play out this way. Every figure here is an estimate, measured against the published timetable from real tracking — not an official number.
Both fleets are placed on the same track using the published route shape, so a crossing on the chart is a real pass on the rail, not an artifact of drawing them apart. Putting the live position of every local and every express train onto one track like this is the piece nobody else has — and it is what lets the app tell you, while you are riding, that a faster train is passing yours and about how long it is likely to cost.
Have an iPhone? Trackside’s app adds live train tracking and arrival alerts — it is in early beta. Request access →
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