and Part II

[Mookie]

A single engine - running up and down the tracks getting ready to be attached to a train - gave me the idea for the question -

What is the top speed of a single, say SD70MAC. You put it on a test track and open it up and it will do what in terms of top speed?

Mook

[Anonymous]

With the proper gear ratio, wheel profile, and proper test track conditions -- the latter two a pair of very big questions -- it might safely be run up to 100 mph. SD40-2s were factory certified for a maximum speed of 65 to 82 mph, depending on gear ratio -- but for 82 mph, you'd need the right track and a good wheel profile to do that every day. E9s with 52:25 gearing were factory certified for a maximum speed of 117 mph.

Most railroads will be setting a maximum speed for an SD70M at 70 mph, and the overspeed will trip a few mph above that speed, say 72-73 mph.

OS

[gabe]

What is the "right track" for high-speed service?

I know it wasn't unheard of in the mid part of the last century for passenger trains to reach 110-120 mph. That was before ribbon rail.

My assumption is probably misplaced, but if they did it in the 50s, wouldn't most well maintained mainlines of today be able to handle 100mph?

Is there that much of a difference in track deterioration at 60mph as compared to 100mph? Or is it other factors of the track that have to be properly maintained--like super-elevated curves?

Thanks,

Gabe

[Modelcar]

...Imagine the forces involved on a large Passenger steam engine running 80, 90...maybe 100 mph with those massive side rods rotating at a blurring speed...!!!

[jchnhtfd]

mudchicken or others can answer this better than I, Gabe, but there are a number of track and track-related factors involved. In many ways the most critical factor is the surfacing of the track -- the exact alignment (local straightness, uniformity of curvature, cross-leveling, and lengthwise leveling -- no high or low spots) of the track. All of the forces acting between the train and the track increase with the square of the speed -- so, for instance, at 100 the forces are about four times as great as they are at 60. If one wants to keep the maximum forces about the same, the track alignment must be four times as good. This is a maintenance issue, as any train moving over the track will disturb the alignment at least a little bit. The maintenance increases for higher train speeds mostly because of this need for increased quality -- although if the quality is allowed to deteriorate then, since the forces are so much greater, it will continue to deteriorate faster and faster! Got to get to it! Then there are such things as proper super-elevation, which needs to be maintained. On tighter curves (well, any curve!) there is a maximum safe super-elevation (it's so embarassing if a stopped train topples off the inside of a curve...) which effectively limits your top speed on that section. One of the reasons for tilting passenger trains (e.g. the Acela) is that the passengers become uncomfortable at speeds well below what the train itself can handle, unless the cars tilt -- but that's another issue.

Ribbon rail helps in the maintenance, because of no joints -- but if the maintenance is done well, stick rail will handle the speeds too. Just more maintenance...

[CShaveRR]

I can vouch for well-maintained jointed rail back in pre-Amtrak days.

I also know that locomotive overspeed trips can be circumvented (don't know how!). With several people checking me out, I was timing mileposts at 35 seconds apart for long distances on the Grand Trunk Western's Mohawk between South Bend and Battle Creek in a desperate (and successful!) effort to make up for time lost at Chicago. The GP9s were geared for 83 m.p.h.; timetable speed was 79 m.p.h., but a mile in 36 seconds is 100 m.p.h.--and we were doing better than that! This was jointed rail.

But I can also vouch for massive cutbacks in employment in track maintenance areas, so that a few years later trackage not only rode rough but actually looked terrible. Welded rail, as Jamie said, eliminates one maintenance headache, but it doesn't mean that the track will stay pristine forever! Some railroads (I can think of one in the east and one in the north--kind of!) haven't caught on to that yet. Every year I spend a little time in August watching the CN go through Schoolcraft and/or Vicksburg, and I just have to sigh and shake my head.

[Anonymous]

It's really not necessary to maintain a lot of tracks like they did in the past anyway.

Since 99% of traffic on MOST railways is freight, there's no need for track to be maintained so trains can be reaching speeds of 100MPH plus.

Most feight trains in my area are lucky if they have the motive power to get up to 60MPH, and even at that rate there's only a few miles of track where they can legally do that speed, otherwise you're looking at pretty much 40-50MPH mainline speeds.

[adrianspeeder]

Adrianspeeder is excited!!! [:p]

SUNDAY....SUNDAY.....SOMEDAY

All AMERICAN drags featuring big block DIESEL locos!!!

Watch GE vs. EMD battles with clouds of SMOKE from turbos pushin MAX BOOST!!!

Who will win????

You just have to BE THERE

Adrianspeeder

[tree68]

I recall reading in an earlier thread that nothing like FRA track standards existed "back in the day." So it's entirely possible that those trains were moving at speeds that wouldn't be allowed today...

Also, IIRC, aren't light engines usually restricted for speed, as compared to an engine pulling a train...