I do like your posts. Keep them coming.

Block lengths are something I've wondered about for some time. Without a certain formula spelled out by the feds, who or what sets the standard? Modern signal designs seem to be moving toward 2 mile block lengths (or even longer) to accomodate heavier 143 TOB freight trains wherever possible. This makes perfect sense to me given the longer stopping distances needed by unit coal or grain trains, which are almost always 140-143 TOB.

One thing I don't understand is why Santa Fe/BNSF prefer longer blocks in mountain territory where trains are already moving sufficiently slow that extra stopping distance isn't necessary. BNSF installed new CTC on the Needles Subdivision about ten years ago and extended the block lengths from about 1.9 - 2.5 to 2.5 - 3.1 miles just about everywhere except at sidings. The latter length was already common on the Cajon Subdivision.

I have to think that either a bean counter or somebody in the signal department made these decisions unilaterally because the result on the Needles Sub was a predictable decrease in velocity. Nobody wanted to play the Restricted Speed game at three miles a block, especially going downhill, so instead of pulling down like they used to do, it was sit and wait for an Approach.