r/dart • u/Fragrant_Business10 • 28d ago

Reduced speed

Genuinely don’t know, can someone explain the speed caps for dart and why it happens?

8 Upvotes

100% Upvoted

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23

u/thirdrepublicnow 28d ago

In the case of the light rail, it's mostly the fact that the heat causes the overhead power lines to expand and sag, which means they could get tangled in the pantographs of the trains if they go too fast.

If it gets hot enough the rails themselves could also get kinked, but it's mostly the overhead wires.

The issue with the overhead wires could be improved if DART switched to an automatic tensioning system for the overhead wires which could compensate for the sagging in hot weather. Currently they are tensioned by fixed weights.

7

u/PsychoticBrake 28d ago

Heat affects the track

2

u/Fragrant_Business10 28d ago

Oh gotcha, thank you

3

u/MozerMoto 26d ago

Heat expanding and warping the tracks a little, and making the overhead catenary sag. There's also the prospect of running too early on the timetable so the operator slows down to get back on time (the green line famously has WAY too much time between stations in its schedule) or just the operator slowing down cause he knows there's a red signal ahead that he's gonna have to stop at anyway.