Why 79 mph

[FTGT725]

Could someone explain why many railroads have 79 mph as the track speed. Why not make it an even 80 Mph?

[CG9602]

One reason is the FRA requirement that, for a route to have a speed limit greater than 79 mph, the route must have either ATS, ATC, or cab signals. The railroads also have to pay for their maintenance and upkeep out of their own funds. rather than pay for the expense of maintaining track to a higher standard, and having to maintain the additional cab signals, and having to outfit all locomotives that use the line with cab signals, or ATS, or ATC, the freight RRs simply place the speed limit at 79 mph, and use Automatic Block signal systems.

If you are asking why the ICC (and, currently, the FRA) arrived at 79 mph as the speed threshold for cab signals / automatic train stop / automatic train control, instead of some other speed, I don't know. Rumor has it that in Canada, the regulations allow for a 100 mph speed limit while using automatic block signal systems.

[timz]

When the ICC set the rule in 1947, apparently their mindset was that RR speed limits were set in stone. They said (roughly) "If your passenger limit is 80 mph or higher, you must have or install blah blah... if your passenger limit is 60 or higher you must have or install blah blah..." They figured they were requiring certain signal installations-- but, it turned out they were actually requiring reductions in timetable speed limits. On many RRs, anyway. One suspects that some railroads dutifully put the 79 limit in their timetables and turned a blind eye to violations-- SAL being a likely example.

[zardoz]

It was a somewhat-arbitrary speed, chosen by factoring in stopping distances, distance between signals, and terrain.  It could have been 75mph just as easily as 85mph. 

A similar situation exists on the highways.  Why 55mph?  Why not 60?  Why not 50? Why not 57?  On city streets--why 25mph, or 30?  It's a compromise.

[timz]

It was a somewhat-arbitrary speed, chosen by factoring in stopping distances, distance between signals, and terrain.

If the ICC had factored those things in, the resulting limit would have been different for each subdivision of each railroad. They had no interest in doing that, even if it were feasible, which it wasn't.

[wjstix]

I think part of it is just that if they said "80" it would be easier to fudge a little and go 82 or 83 or whatever. "79" makes it clear that you can't go 80 or faster. Kinda the same thing that makes something costing $1.99 sound a lot cheaper than something costing $2.00.

[traisessive1]

VIA goes up to 100mph and does not have cab signals.

[CSSHEGEWISCH]

VIA goes up to 100mph and does not have cab signals.

The ICC did not have any jurisdiction outside of the United States.

[chefjavier]

What about track perfomance? Does hold for the speed limit?

[JT22CW]

IINM, the top speed allowed for CTC in pretty much the rest of the world is 100 mph.

[traisessive1]

The track is the same crap CN track as everywhere else. It's dangerous track. Just the coaches that have the tilt capabilities (LRC coaches) can do the 100mph.

[Railway Man]

In the U.S., maximum speed limit has both a track geometry/defect limit and a Method of Operation limit, whichever is more restrictive is the one that applies:

Track speed limit, as proscribed by 49 CFR 231.9 and 49 CFR 213.307, in mph:

Track Class		Freight		Passenger
Excepted track		10                N/A
Class 1 track		  10                 15
Class 2 track		  25                 30
Class 3 track		  40                 60
Class 4 track		  60                 80
Class 5 track		  80                 90

Class 6 track...110 m.p.h.
Class 7 track...125 m.p.h.
Class 8 track...160 m.p.h. 
Class 9 track...200 m.p.h. 

Method of Operation speed limit, as proscribed by 49 CFR 236.0:

    (a) Except as provided in paragraph (b) of this section, this part 
applies to railroads that operate on standard gage track which is part 
of the general railroad system of transportation.
    (b) This part does not apply to rail rapid transit operations 
conducted over track that is used exclusively for that purpose and that 
is not part of the general system of railroad transportation.
    (c) Where a passenger train is operated at a speed of 60 or more 
miles per hour, or a freight train is operated at a speed of 50 or more 
miles per hour, a block signal system complying with the provisions of 
this part shall be installed or a manual block system shall be placed 
permanently in effect which shall conform to the following conditions:
    (1) A passenger train shall not be admitted to a block occupied by 
another train except under flag protection;
    (2) No train shall be admitted to a block occupied by a passenger 
train except under flag protection;
    (3) No train shall be admitted to a block occupied by an opposing 
train except under flag protection; and
    (4) A freight train, including a work train, may be authorized to 
follow a freight train, including a work train, into a block but the 
following train must proceed prepared to stop within one-half the range 
of vision but not exceeding 20 miles per hour.
    (d) Where any train is operated at a speed of 80 or more miles per 
hour, an automatic cab signal, automatic train stop or automatic train 
control system complying with the provisions of this part shall be 
installed.

RWM

[Anonymous]

We can forget HST, TGV's and Bullets then.

Getting an Agency to change speeds higher (Much higher) is like trying to tow Mt Everest.

Personally I think if 80 is good, 110 is better but not much.

So much for the Milwalkee track sign "Slow to 90"

[Railway Man]

We can forget HST, TGV's and Bullets then.

Getting an Agency to change speeds higher (Much higher) is like trying to tow Mt Everest.

Personally I think if 80 is good, 110 is better but not much.

So much for the Milwalkee track sign "Slow to 90"

Not so -- it's just "forget about it" with track and train-control system that doesn't meet the requisite FRA standard.

There are two advantages of increasing speeds from 80 mph to 110 mph -- better platform-to-platform times and increased track capacity.

RWM 

[chefjavier]

In the U.S., maximum speed limit has both a track geometry/defect limit and a Method of Operation limit, whichever is more restrictive is the one that applies:

Track speed limit, as proscribed by 49 CFR 231.9 and 49 CFR 213.307, in mph:

Track Class		Freight		Passenger
Excepted track		10                N/A
Class 1 track		  10                 15
Class 2 track		  25                 30
Class 3 track		  40                 60
Class 4 track		  60                 80
Class 5 track		  80                 90

Class 6 track...110 m.p.h.
Class 7 track...125 m.p.h.
Class 8 track...160 m.p.h. 
Class 9 track...200 m.p.h. 

Method of Operation speed limit, as proscribed by 49 CFR 236.0:

    (a) Except as provided in paragraph (b) of this section, this part 
applies to railroads that operate on standard gage track which is part 
of the general railroad system of transportation.
    (b) This part does not apply to rail rapid transit operations 
conducted over track that is used exclusively for that purpose and that 
is not part of the general system of railroad transportation.
    (c) Where a passenger train is operated at a speed of 60 or more 
miles per hour, or a freight train is operated at a speed of 50 or more 
miles per hour, a block signal system complying with the provisions of 
this part shall be installed or a manual block system shall be placed 
permanently in effect which shall conform to the following conditions:
    (1) A passenger train shall not be admitted to a block occupied by 
another train except under flag protection;
    (2) No train shall be admitted to a block occupied by a passenger 
train except under flag protection;
    (3) No train shall be admitted to a block occupied by an opposing 
train except under flag protection; and
    (4) A freight train, including a work train, may be authorized to 
follow a freight train, including a work train, into a block but the 
following train must proceed prepared to stop within one-half the range 
of vision but not exceeding 20 miles per hour.
    (d) Where any train is operated at a speed of 80 or more miles per 
hour, an automatic cab signal, automatic train stop or automatic train 
control system complying with the provisions of this part shall be 
installed.

RWM

RWM

Great Info.What is our current track class in Regional & Shortline Railroads? Do we have anything higher than Class 7 in U.S.? I know in Europe is higher..