Lower Saucon (Bethlehem), PA Derailment, 3/2/24

ExCon90 wrote:

jonnhrr wrote: ↑Sun Mar 03, 2024 9:54 pm I thought PTC was supposed to make collisions like this impossible

Once the first 2 trains collided --for whatever reason -- and fouled the adjacent track, PTC could not have prevented the sideswipe of the wreckage if the 3rd train had come along soon enough afterward.

Why didn't PTC prevent the rear-ender? I presume there is some provision for a following train to approach one ahead under controlled circumstances but obviously there are still gaps in the technology.

That's the key question; rear-enders are exactly what PTC is supposed to prevent -- even, if necessary, by sensing that the engineer isn't going to stop and preventing a collision before it happens. We'll have to wait quite a while before we see the NTSB report -- that part should be particularly interesting. It may turn out that somebody cut something out to save time and trouble.

PTC is designed to prevent head on collisions and stop signal violations, not rear end collisions. If you are following a train PTC will require you to operate at restricted speed. If you exceed restricted speed you will get enforced by the PTC system. If you are below the speed threshold for restricted speed, you don't get enforced.

Then how is it different from cab-signal systems that have been in effect for decades? They protect against rear-enders in exactly that way, including overrunning stop signals -- as long as you stay under 15 mph you can keep going until you hit something. I thought the whole point of PTC was that it detects, among other things, whether a train is accelerating or decelerating in approach to a signal, and if moving too fast to be able to stop, stop the train before it reaches the signal.
















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PTC is basically a higher tech version of a cab signal/LSL system. The computer screen shows a map of the route and has all of your train information in the system to approximate stopping distances. If you are running on clear signals in 50 mph territory and the engineer allows the train speed to get to 53 mph you will get a penalty brake application from PTC for excessive speed. If you have an approach signal and the next signal is a stop signal the PTC screen will show that to the engineer. It gives you a distance countdown to the stop signal and the algorithm determines, based on the information for your train, if you are slowing down enough to stop at the signal. If the PTC system determines the train isn't slowing down enough when approaching the stop signal PTC will initiate an emergency brake application. PTC does not tell you what trains are ahead of or behind you. So if a train is stopped ahead PTC shows the engineer that they must operate at restricted speed in that block, but it doesn't give you any other information as to the reason for the restricting signal. Maybe PTC version 2.0 will address that shortcoming.

But cab signals weren't automatic, were they??
The NYC had a separate system ATS (Auto train stop), but that was different.

On the PRR, if cab signals also had automatic speed control, each signal indication was associated with a maximum speed; i.e., Approach Medium = 45 mph, Approach = 30 mph, Restricting = 15 mph. At an intermediate point in each block there was a code change point that would drop the cab signal from Approach to Restricting if the next block signal was displaying stop. If the train exceeded the maximum speed for the signal last passed the train would be brought to a stop, but the system did not enforce timetable track speed. Amtrak later installed ACSES (Automatic Civil Speed Enforcement System?) on the NEC after making a few location-specific installations and was in the process of installing it on the entire NEC at the time Train 188 was wrecked at Frankford Jct. (At the time it was already in place westbound but not yet eastbound.) In all instances a violation had to occur before any automatic stop was triggered.

No one mentioned what type of line this is.
Is this double track, or just single with passing sidings?
Also what/where are the two points/towns etc this line comes from and goes to? I assume it was originally PRR trackage.

Mostly single track now with sidings. It's the former LV between Allentown and Manville. The PRR went from Manunka Chunk under the LV at Easton/Phillipsburg to Trenton.

There is an active railcam at PU tower in Phillipsburg about 10 miles east of the crash site where NS runs over a portion of former CNJ track.

Ok, that answers alot, I knew it wasn't the PRR main line.
Then this 268 rear-ended the 24X which were on the siding waiting for 19G to pass. Must be a awful long siding to fit two trains.
The two units that were down the embankment, were both off that westbound?

Of those screen shots that I posted, do any show the exact location of the derailment? I do see alot of curves that would limit the crews visibility with all the trees and vegetation..

After looking at the photos, and noting the wires in one angle, I believe we're looking about here, just east of MP 84:

2400 Riverside Dr
https://maps.app.goo.gl/auezadXrG5Rn25pD9
The #2 main runs from Easton to a point about 6 miles west of the crash site. MAS is 40 according to the 15 year old TT I have for that section, and there's a big curve near the junkyard, right before the derailment site.

Yes, both units in the drink came off the WB 19G. That road is really narrow through there, so closing it made plenty of sense for the first responders.

Good call, thanks!
So that entire area in the screen shots, including the widest view was basically double track?
What I didn't ask, what was the CP (Control Point) where the 1st EB was being held?

Must have been Richards, MP 81.1.

24X was stopped at Readington interlocking. CP Richards was retired several years ago.