What is the effect of train speed on track maintenance? If speed over a line is increased 10%, does the cost of maintaining the line go up an even 10% as well?
In the world of physics, most things related to velocity increase as a squared power (or more), not linear as you asked/ suggested. In the absence of a detailed study or report (there’s some out there, but not handy to me at the moment) , for track - rail, ties, ballast, accessories, etc.* - I’d tend to say that holds true here too. So, per your question of a 10% speed increase, I’d say the track maintenance cost would increase by 1.10 x 1.10 = 1.21 or 21% - say, 20 % for simplicity. Likewise, a 50% increase in speed - say, from 40 MPH to 60 MPH - would be 1.50 x 1.50 = 2.25 or 125 % more expensive. Maybe that’s a little heavy, but not far off. Of course, this is a perfect instance of “YMMV” (Your Mileage May Vary").
*Since your question asked about “the cost of maintaining the line” [emphasis added] and not just “track”, I’d say the increase would also include bridges, esp. steel open-deck types, but not masonry ballast-deck bridges, tunnels, earth fills and cuts, etc.
- Paul North.
That’s a case by case issue. It isn’t lineal and the variables can bite you.
Also, the older the track structures get, the worse it gets.
(If they hadn’t wasted all that money on shiny new toy locomotives and not deferred maintenance, the outcome in many places would be different. But track isn’t sexy to an upper operating bubba.)
As speeds increase so does the standards of maintenance required by FRA Regulations.
So increacing sppeds requires more MOW work on rails, ties and ballast. That makes sense. Does it also increase the upkeep on bigger things, like bridges and tunnels?
(1) increase in speed requires increase of inspection interval and tightens the allowances. Maintenance costs are directly tied to degradation of the track structure. That is more a function of local conditions, train frequency and tonnage. As much as you want to lump things together, you really cannot. (nature of the beast)
(2) Same comment applies to bridge strutures. The FRA bridge rules look more at loading cycles, design strength and train weight as a function of time. Why should it apply to tunnels? Outside of impact loading, why should speed be an issue if the bridge is in good repair???
There is also the factor of diminishing returns. A higher speed might seem like a good idea, but in many locations the increase in speed over a certain amount doesn’t really do that much good. In addition, there is the proportionately higher increase in fuel consumption to get up to the higher speed.
Sure, if an entire subdivision has straight-shot running with no meets, no permanent speed restrictions, then the speed returns are higher. But if the track has a few timetable speed restrictions (junctions, curves, interlockings, etc), then additionally factoring the need for braking and accelerating, the speed advantage is greatly reduced. If it takes a train 2-3 miles to accelerate an extra 10 mph, then in a few more miles it has to slow down again, what is the point of the higher speed?
If you go 200 miles at 70 mph it will take you about 2 hours 53minutes. If you go 60mph, it will take you 3 hours 20 minutes. A maximum savings of only 27 minutes (not counting accelerating and braraking, which would reduce the difference even further) over 200 miles is hardly worth the added expense of maintenance, unless the route if for very time-sensitive freight, which should be charged at a higher rate to offset the cost of maintenance. That 27 minutes could easily be eaten by just one malfunctioning signal or having to stop to reline a switch.