79 mph speed limit

[RudolfJan]

Hi all,

Grown up with decimal systems, I am curious why some US routes have a 79 mph speed limit (at least, this is used in Trainsimulator). Why 79 mph and not 80 mph? I also saw a 44 mph limit, really amazing ...

[GreatNortherner]

Hi,

The 79 mph came about because anything 80 and higher would have required the RRs by law to install cab signaling for that line, which not many elected to do because of the costs. So 79mph is as fast as you can go using standard trackside signals and speed signs.

Other "odd" speeds probably had similar explanations. For example, much of the GN's Butte Division had a top speed of 49 mph because it was unsignaled ("dark", train order operations throughout).

Here's a neat summary:
https://en.wikipedia.org/wiki/Rail_spee ... ted_States

Cheers
Michael

[BNSFdude]

49 is Dark Territory speed limits. Any higher required at the minimum ABS signalling. However, with the advent of PTC being able to be used in bonded "dark" territory, I'm not sure if that'll allow the speeds to be bumped up or not.
Bonded dark territory being that the tracks have track bonds and blocks just like CTC and ABS territories without the signals to protect from conditions such as broken rail or open switches. BNSF has been pairing this with what's called "RCPS" or, Remote Controlled Power Switches at sidings creating Control Points much like CTC, again, without the signalsupport.

As Michael said, anything over 79 requires either Cab Signalling or ATS, but like I stated earlier, that may change with PTC requirements in the next two years.

[RudolfJan]

Thanks for your replies!