How Treated Trestles Built the American Rollercoaster

A trestle is the simplest type of three-dimensional construction, but build hundreds—or even thousands—of trestles and you have a trestle structure, a series of repeating triangles that can be shaped into most anything. Like a piece in a child’s set of building blocks, the humble trestle can transform into all types of structures, including bridges.

Trestles comprised of untreated wood were originally employed as more temporary structures. But with the advent of creosote treatment technologies, trestle structures took on more long-lasting, useful, and interesting forms.

The Development of Modern Trestle Bridges

Trestle bridges have been constructed since at least the 1700s. Historically, they were temporary structures, built to facilitate a larger construction project like the scaffolds that surround high-rises as they go up. This is likely because pressure-treatment with creosote preservative, which extends the service life of wooden infrastructure by decades, was not available until the mid-1800s when the Bethell process helped fuel the Industrial Revolution. Trestle bridges were often built to access hard-to-reach locations, and move material from that location, after which they were destroyed or filled in with another material to make them permanent.

But just because trestles are simple does not mean they are weak—especially once pressure-treatment with creosote wood preservative became commonplace in the 1900s. The new Rueping and Lowry empty-cell processes made wood preservation much more efficient and cost-effective and remain the methods of choice for creosote wood treatment today.

Many treated-wood trestle bridges developed at that time remained in place for several decades, such as the Kinsol Trestle on Vancouver Island, Canada. For nearly 60 years, the trestle bridge connected Victoria to Nootka Sound to transport timber from this remote location. Built by the Canadian Northern Pacific Railway in 1920, the Kinsol Trestle is one of the highest wooden trestle bridges in the world and traverses complex terrain, including an impressive 7-degree curve. The bridge’s Douglas fir beams, and the pilings that reach in the Cowachan Lake, withstood deformation and decay for decades. In the Kinsol Trestle’s 2011 rehabilitation, a detailed evaluation determined that a majority—60 percent—of its timbers could be preserved rather than replaced.

The porous nature of a trestle bridge, with so much open space, can also be advantageous. The Goat Canyon Trestle Bridge in San Diego County, CA, is the largest all-wood trestle structure in the world, constructed in 1933 after tunnels through the Carrizo Gorge for the San Diego & Arizona Railway kept collapsing. Unlike a more solid design, the trestle bridge is undisturbed by extreme weather, such as high winds and rushing water; Goat Canyon’s trestle was actually designed specially to withstand high winds using a 14-degree curve. Furthermore, since treated wood withstands high temperatures better than metal, the trestle was built strictly with wood and no metal nails, possibly utilizing wooden dowels or a tongue-and-groove method instead. The trestle supported passenger and freight trains across the gorge for more than 70 years, until rail service was discontinued in 2008. However, the trestle still stands strong and, today, is a popular hiking destination.

Trestle Bridges + Railroads = Scenic Railways and Rollercoasters!

So in 1827, when the Lehigh Coal & Navigation Company needed to do both of these things—extract hard-to-reach-material and run railcars with both passengers and freight throughout its mining operation—it is no wonder that trestles were in order. Nestled in Pennsylvania’s Pocono Mountains, known as the “Switzerland of America,” the Mauch Chunk Switchback Railway was constructed essentially as the conveyer belt for the company’s anthracite coal mining operation. The railroad navigated the uneven terrain of the mountainous mining region, supported by trestles where there were dramatic changes in grade.

An 1832 portrait of the terminus of the Mauch Chunk & Summit Hill Railroad and the coal loading chutes below by Karl Bodmer. Public domain.

Small cars were pulled up by working animals to the peak of Summit Hill on railroad tracks; this “Back Track” used trestles to span the huge slump between the engine house’s peak to the east and Mt. Pisgah’s ridge 475 feet to the west. The cars were then filled with anthracite coal by workers and sent free-falling down the mountain, where a sophisticated turntable-chute-hopper contraption waited to receive the coal. Designed by Josiah White, one of the engineers of the Lehigh Canal itself, this hopper expertly sorted and then dropped the anthracite, a shiny, metamorphic rock known as “hard coal,” into a shipping vessel which then floated this valuable material down the canal to the Philadelphia market.

But how did the cars come down the mountain safely? The free-fall down the railroad’s “Down Track” was controlled by a “switchback” design which took advantage of gravity’s downward pull but didn’t allow the cars to lose control. The loaded cars were sent down Summit Hill on a zig-zagging track, each leg of its path “switching back” or turning sharply, approximately 180 degrees, to keep cars maintaining a steady speed, like a novice skier slowly zig-zags his or her way down a ski slope. The cars were also equipped with emergency braking mechanisms that kicked into action if they picked up too much speed.

From Transporting Coal to Entertaining People

Given Mauch Chunk’s sprawling valleys and wide views, passersby could view the miners’ activity throughout the day. Coal miners and even the working animals rode inside the small railway cars across multiple peaks and valleys, so why couldn’t locals? In the mid-1800s the railway attracted an increasing amount of interest from laypeople, and in 1846 the cars were upgraded to Barney pusher cars controlled by a steam-powered cable pulley system.

This improvement made riding the “Switchback Gravity Railroad” or “The Switchback” for short more feasible for visitors by reducing the 18-mile round-trip from 4.5 hours to just 80 minutes. Tourists could hop in rail car—which by the turn of the 20th century had more comfortable cars specially developed for tourist passengers—that took approximately an hour to climb uphill on the Back Track and raced down the zigzagging Down Track in just 30 minutes.

All at once, the mining operation had invented the nation’s first “scenic railway”, best captured by the uphill experience of the Back Track with its dramatic open-air views, as well as the nation’s first rollercoaster, exemplified by the thrilling speeds of the Down Track’s switchback gravity railroad. Throughout the early 1900s, the Mauch Chunk Switchback Railway was one of the busiest tourist attractions in the United States; in fact, it was second only to the majestic waterfalls of Niagara Falls in neighboring Upstate New York. Although The Switchback was built before pressure-treating wood was commonplace, the rollercoaster became most popular after empty-cell pressure-treatment methods were in regular use. Thus, in the latter half of its lifetime the ride was surely serviced and repaired using treated wood, enabling it to be safely enjoyed for decades until the ride closed entirely in 1932 during the Great Depression. But its legacy would be replicated for the next century and beyond, starting with the construction of America’s first amusement park rollercoaster in 1884, fittingly named “Switchback Railway,” on New York’s Coney Island.

Note: This article was originally published in the July/August 2024 issue of the Railway Tie Association’s Crossties magazine.