It’s the slide season again. Locomotive engineers creeping past Everett cast anxious eyes at banks looming above, and with good reason; Burlington Northern-Santa Fe (BNSF) has a history of landslides blocking tracks. Though BNSF management surely considers these earth-shifts a threat to be dealt with, there seems to be no cure.

But there may be an identifiable cause. Science and experience tell us that landslides are caused by geology, gravity, weather, groundwater, wave action and human activity. Couple two or more together with steep topography and bad things can happen. In the case of Puget Sound’s high banks, all but one of those factors can act at one time — shore-hugging rail lines pretty well rule out wave action.

The stones and granules and clay that compose local banks rest easy most of the time. Like in DOT’s pyramids of traction sand, they interlock and use friction to resist the pull of gravity. They shift a bit with minor disturbances until collisions with new neighbors produce a new equilibrium … unless the disturbances continue and unless friction with neighboring particles becomes lubricated with water. That’s when solid banks turn to liquid.

Of all the causes of landslides, its human activity that deserves most attention, especially the role of heavy trains massaging tremors into local geology. The reason the train-problem has become more acute is that trains are now longer and heavier than they were when rail engineers first established the route along Puget Sound.

The evolution of locomotives deserves attention. The Civil War era steam engine (named the William Crook) that first traveled the Great Northern route to Seattle was a far cry from modern locomotives. With only a few hundred horsepower, it pulled a dozen or so cars, each shorter and lighter than anything you’ll see today.

We need a sense of how rail equipment has changed. This is a quantitative issue that hinges on measures like tons and horsepower, and changes over time. Everything about trains has grown, possibly to a point where they’ve become an uncomfortable fit for certain routes that were engineered for their steam-powered ancestors.

The William Crook was a wood-burning locomotive weighing 55,400 pounds. Compare that with the popular General Electric diesel-electric Model AC6000CW that tips the scales at 423,000 pounds and delivers 6,000 horsepower. That model went out of production in 2001 to make way for even more powerful locomotives.

The difference in power between the William Crook and GE’s powerhouse enables a huge increase in the number and weight of cars that make up a train. The practical limit on weight and length continues to be pushed higher as evidenced by a record-setting 3.5 mile-long 295 car train that recently traveled from Texas to Long Beach, Calif.

Rail cars of 1937 maxed out at 40 feet in length. By 1953 they topped out at 42 feet, 3 inches. Now, rail cars measure just short of 80 feet so a hundred cars from the ‘30s would measure a bit more than half the length and less than a quarter of the weight of a modern train. While increased length causes trouble at grade crossings, it is weight that really shakes things up.

Freight cars of 1880 weighed 25 to 40 tons loaded. By 1910 gondola cars regularly weighed 55 tons. By 1970 the load had grown to 70 tons and over the years since, cars have weighed in at 60, 80 and even 100 tons. All this increase rides on routes engineered for lighter, shorter trains of another era.

The current concern is coal trains. A loaded coal car weighs 286,000 pounds, 140,000 pounds of which is coal. Each car is 4.5 times as heavy as early bulk cars and five times as heavy as the first engine to travel the route. The diesel-electric locomotive that pulls them is 7.5 times as heavy as the old William Crook steamer.

Roadbeds have certainly been upgraded to keep increased loads from crushing rails into underlying soil but little has or can be done to upgrade surrounding geology. While early trains barely tickled the terrain, modern behemoths deliver a penetrating massage that rattles foundations of brink-dwellers whose view properties are put in peril.

BNSF keeps track of roadbed vibrations with a gadget called the “Snapshock Plus,” an acceleration recorder. This device, no larger than a paperback novel, measures vibrations caused by moving trains and the impacts of switchyard humpings and couplings. It would be interesting to see how read-outs from these little instruments correlate with landslides.

Put a wet winter together with hundreds of 143-ton coal cars rumbling past the base of unstable banks and you have a recipe for landslides. It’s not a matter of whether, but when. The certainty of slides begs the question, should coal trains determine whether a rail line that serves many needs be victimized by interruptions?

Comments may be addressed to robertgraef@comcast.net.