Everything you always wanted to know about...ballast

[CHamilton]

Why You Always See Crushed Stones Alongside Railroad Tracks

...The crushed stones are what is known as ballast. Their purpose is to hold the wooden cross ties in place, which in turn hold the rails in place.

Think about the engineering challenge faced by running miles of narrow ribbons of steel track on top of the ground: they are subject to heat expansion and contraction, ground movement and vibration, precipitation buildup from rough weather, and weed and plant growth from underneath. Now keep in mind that while 99% of the time they are just sitting there unburdened, the remaining 1% they are subject to moving loads as heavy as 1,000,000 pounds (the weight of a Union Pacific Big Boy locomotive and its tender)....

More details in the original article.

 

[xyzzy]

Ballast shoulder width and slope are important to prevent sun kinks. Most railroads want 12 inches of BSW on heavily-used lines. The track above appears to be less than 12 on the right shoulder.

 

[Aaron]

When I was a kid, all the ballast that I ever saw was very dark colored rock, so I just assumed it was coal. I thought that's how they keep the locomotives running. When they need more coal, they just reach a shovel down, scoop some up, and toss it in the firebox. I guess I thought there was some other division of the railroad that was responsible for running around the whole country spreading coal on the sides of the tracks so that the other trains would have a way to get fuel while they were running.

 

[GG-1]

When I was a kid, all the ballast that I ever saw was very dark colored rock, so I just assumed it was coal.

Aloha

Growing up on the east coast I thought the same. I was so surprised when I saw western Ballast was red in the desert. And I Hawaii the ballast was white since much of it was made from coral.

 

[George_Harris]

Where do I begin? The discussion in the link is fairly simple minded. There as several things that are made as absolute pronouncements which are anything but absolutes. The American Railway Engineering and Maintenance of Way Association (AREMA) specifications for ballast runs to 20 something pages. It also makes quite a few pronouncements about tie sizes and spaces that are anything but universal absolutes. Wood ties can vary from 6" x 8" x 8' up to 7" x 9" x 9'. Yes, 7" x 9" x 8'-6" is the most common size for wood ties, but far from universal. Concrete ties are in the same general size range, but usually not exactly rectangular solids. Tie spacing is usually not less than 19 1/2 inches for wood ties but frequently more. 21 inches is also common. For lightly used track the space is commonly 24 inches. For transit systems with their light axle loads wider spaces in the 24 to 27 inch range can be common. With concrete ties, 24 inches is common in railroads and 30 inches in transit lines. Ballast shoulder width is commonly 12 inches but may be other dimensions. The side slopes may be 2:1, but may be 1.5:1. Depth under tie is usually 12 inches minimum, but may be another dimension. Usually there will be a layer of aggregate similar to a highway base course under the ballast, usually 6 inches or more in depth, depending upon underlying soil conditions, traffic volume, and axle loadings.

 

[benjibear]

The picture looks like my model railroad trackwork!

 

[SarahZ]

When I was a kid, all the ballast that I ever saw was very dark colored rock, so I just assumed it was coal. I thought that's how they keep the locomotives running. When they need more coal, they just reach a shovel down, scoop some up, and toss it in the firebox. I guess I thought there was some other division of the railroad that was responsible for running around the whole country spreading coal on the sides of the tracks so that the other trains would have a way to get fuel while they were running.

That's adorable.

Ballast is the #2 reason (the first being the train) that I stay far away from the tracks when a train is coming. When Amtrak passes through my neighborhood, it kicks up quite a bit of ballast, and those stones get thrown a good 10 feet.

 

[xyzzy]

Ballast is the #2 reason (the first being the train) that I stay far away from the tracks when a train is coming. When Amtrak passes through my neighborhood, it kicks up quite a bit of ballast, and those stones get thrown a good 10 feet.

That's correct. Experienced railroaders keep their distance from every passing train and, whenever possible, look for where to run or jump if a shifted load (for example) is coming their way. I've seen the general public and railfans/photographers get way too close, relative to what I was taught.