Quote:
Originally Posted by BG918
The DIA station has room for one more platform and two additional tracks that could be used for an express train in the future. At least they planned ahead there. Downtown-DIA in 23 minutes would be amazing. What will it be with 8 stations, I've heard 38 minutes but that seems too fast with that many stops.
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The problem, sir, is not the terminal ends-DUS and DIA but the lack of 3 or 4 tracks at any intermediate stations.
Expresses force slower traffic ahead of them and going in the same direction to pull off the main track.
Let's say an express leaves DIA and takes 24 minutes to get to DUS. That means that any train ahead of the express has 24 minutes to get to DUS. Assuming the DIA train takes 40 minutes, that means a DIA train will catch any local train that left DIA in the last 16 minutes. But, the problem simply is not with that train. This mans that any train ahead of the 2nd train has to be able to get to DUS in 24 minutes or less also. Assuming a 15 minute buffer between trains and the additional complexity for scheduling over the single track interval, then this express indirectly affects scheduling as close as 9 or less minutes out of DUS at time when the train leaves DIA for DUS. Put stations into the equation and the relationship becomes more complex. Without passing tracks, trains travel the line at the speed of the slowest train of any train in front of the express at any given time, i.e., take the slowest of trains ahead at time T then take the increment of that slowest speed, and, that affects all travel in that direction at the time the slowest train travels that increment.
With passing tracks the minutes added for trains to wait being passed can be subtracted from express train's travel time to a maximum track speed. Over most of the DIA line this will be 79 mph.
With 3 track stations (the center being switchable passing track that take traffic from both directions, trains going in the same direction can pass one another. You don't need more than two or three 3 or 4 tracked intermediate stations to enable 5 or even 4 minute headways while running expresses (figure is higher due to single track sections.)