Train exiting the Tehachapi Loop - GIF

[Altair]

Train exiting the Tehachapi Loop in Kern County, California.




Previously:

Train pulls out of a turn - GIF
Constructing a tunnel under a highway - GIF
Monorail track switching - GIF
Leggers moving a boat through a tunnel - photos

[capngeo]

Thats a lot of tractive effort!

[jimfols]

Rising at a steady two percent grade, the track gains 77 feet (23 m) in elevation in the Loop

[Drew1966]

Is a consist that long Really safe though? It’s a long way for the air pressure to flow and make the safety brakes work.

[jimfols]

Is a consist that long Really safe though? It’s a long way for the air pressure to flow and make the safety brakes work.

This is not a direct answer to your question but a good example of what a PIA it must be to fully understand the system.
Long video but well worth the time if interested in the subject.

[jimfols]

Here's one explaining the EOT (end of train device). Long 17 mins. 8:55 explains failures.
Interesting thing I learned, the rules seem to change at +/- 2% grade.

[Drew1966]

They were interesting, thank you Jim. But I still think that a consist that long could be dangerous, mostly due to the time it would take for the pressure to release from the brake lines along the entire length of the consist.

[jimfols]

I always say if you can't explain it you don't understand it. And I can't explain it.
I believe it has a lot to do with the lowering of the brake pipe pressure just a small amount controls the AB valve in each car which controls a cylinder full of air to apply the brakes on that car.

This is from John Bentley
At tarorigin.com

SERVICE BRAKES: This is the type of brake application normally used for braking. This level of braking is achieved with a 6psi to a 26psi reduction in the brake pipe pressure. When the AB valve senses the difference in pressure air is ported from the reservoir to the brake chamber. Air pressure acts against the diaphragm and brakes are applied. Braking with the Service Brakes offers up to 75% of a train's Emergency Brake capability

[Frank S]

My bud will buy an older trailer usually a specialty unit like a sliding axle tilt bed or a RGN either mechanical or hydraulic then haul them out to me for evaluation. They almost always require brake replacements so He considers that he is going to have to spend 3 to 6K or more before buying one. At an auction several years ago now he and I spotted a Traileze hydraulic flip tail with a badly compromised frame right behind the neck I convinced him to bid on it. Anyway he made a bid so low that we could have tripled our money just by cutting it up and hauling it to the scrap and no one bid against him. I bought about 25,000 lbs of stuff with the intention of much of it being turned into scale bait. but there were a pair of long heavy H beams in what I bought. We used those to stiffen the neck on the trailer by chaining them down and had everything else loaded on it. On the way home with our bounty I said you know I bet for less than 10 grand I can turn this trailer into something worth selling. Anyway a thousand dollars worth of T1 steel new brakes including shoes kits drums slack adjusters S cams chambers the antilock valves and sensors air lines hydraulic hoses and repacking the cylinders plus 8 new tires and a little paint and lights the trailer was roadable enough that he pulled it for nearly 2 years. He kept track of the added revenue it brought in over just a step deck or a flat bed and figured it paid for itself in the first 9 months. One day someone offered him too much money for it so he sold it and bought an aluminum step deck and a tandem sliding axle landol with the money from the Trail eze plus another aluminum flat bed the step deck cost him 10,000 and the landol cost 12,000 the flat bed could eventually wind up as scale bait. but I put about 5K in parts and labor in the landol and he has 2 trailers that he can pull Right now I have a 3 axle Kaylin Siebert sliding axle of his to rebuild for him.

[Frank S]

They were interesting, thank you Jim. But I still think that a consist that long could be dangerous, mostly due to the time it would take for the pressure to release from the brake lines along the entire length of the consist.

Actually the one shown probably isn't even considered a long train but since we can't see the rear it could still have more than double the amount of wagons we can see that haven't come onto the scene. From the looks of what I could see there may have been around 100 wagons almost all of them were container type many were double stacked. You will often find up to 160 wagons for each 2 locos across the plains, fewer for mountain passes. so more probably 100 to 2 with possibly or probably 1 or more locos in the rear. For the really long trains you see crossing Lower Arizona you might see 2 locos placed near the center as well, a lot depends on what the freight is. Containers are usually much lighter than coal, Iron ore, or crushed rock. So less tractive force is required for the double stack container unit train than one of other comedies or mixed wagons. On our last trip to Seattle we saw several trains over 3 miles long.
A railway worker once told me they are more concerned with tractive force than braking force because it is not as if you are going to be stopping at the next intersection when the light goes red like in a car. They plan their slow downs miles in advance.