Braking Trolleys

Safe Ziplining

The Richardson Safety Trolley (RST) history began in 2001 when we—AA Machining & Welding, Inc.—designed and manufactured a 60-mph RST for the 2002 giant zipline at Park City Mountain Resort (PCMR); the 3,500-foot-long zipline broke records with a 600-foot drop between platforms. Since then, over fifty ski resort ziplines have utilized RSTs; our RSTs have an unblemished safety record with zero braking accidents. We continually strive to improve our auto-braking trolleys to function correctly for our customers. If a design fails to meet our client's expectations, we replace their RST with an improved version at no charge.

Our company established Momentum Engineering in 2015, and we began testing our sixth-generation RST as a 3-lb. trolley for zipline tours. Testing for the RST-22 began during the summer of 2022, and it performed flawlessly; the RSTs safely stopped every time on a 10-degree slope; we found that pin/slope setting #8 was ideal and the RST was five settings away from the wheel—less braking force—so we shipped the RST to an east African zipline. We soon found their three-degree slope was no match for our trolley's fastest setting, #3—the lowest brake force—our RST stopped 100 feet short of the platform. We learned that the RST needed one more pin/slope setting next to the wheel. So, we expanded the lever arm and slot to show numbers #2—#14. Our 3D designs became the RST-23FS, and we sent our design to laser cutters for the new trolleys' side plates (see Image 1; red arrow) at #2.  

The Richardson Safety Trolley rests on a zipline cable (see blue arrow). The vertical lever arms with circular handles identify the current #5  pin setting. Notice that the participant's carabiner (see purple arrow) connects below the handles in one of the pin/slope settings to vary the amount of brake force.

Every zipline slope varies as adventurers zipline over scenic terrain, so our test RSTs have over a dozen lever arm adjustments (pin/slope settings) to stop zipliners.

To adjust the lever arm, remove the safety pin (see Image 2; orange arrow) and use the handles to lift the two lever arms and then horizontally adjust to the desired setting; then lower the lever arm and replace the safety pin.

The fastest speed setting is #2, and #14 is the slowest because it is closest to the RST brake (see green arrow).

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The advantage of RSTs over free-wheeling trolleys (two wheels) is the RSTs' slope adjustment—via pin/slope settings—to equalize the slope for all zipliners and control their arrival speed.

The Petzl® two-wheel trolley is compared in this video to the RST. The zipline slop is 10-degree at the beginning and shows a 22-MPH free-wheeling Petzl trolley, and RST-22 slows to 2-MPH as it arrives. All test weights in the video use the same RST pin/slope setting #8. Establishing pin settings slows an 80-lb. RST zipliner with their 80-lb. brake force—on the same slope—as a 250-lb. in the same setting. Each zipliner applies RST brake friction with their weight (mass)—gravity is constant—to stop them safely. Notice in this 2019 RST video using the same pin/slope setting to stop all weights. So, each RST setting is tested to establish stop locations and reduce RST rollback, eliminating all patron retrievals nearly every day with two-wheeled trolleys.

In 2019, our telescoping spring patents solved that problem, and their different compression rates (pounds per inch) soften all stops. Our springs install in minutes, meet the standards, and, when properly designed and implemented, they eliminate lawsuits. We design our products to protect zipliners' well-being and owners' bottom lines.

Industry Standards

Ziplines standards require a minimum 3:1 engineering factor of safety (FoS) or safety factor (SF). The FoS or SF guides the zipline engineer or designer to address the intended loads or level of safety required. For example, if a device breaks one pound above its maximum load (1,000 lbs.), and the standards require a 5:1 FoS, the load must not break or fail with a 5,000 lb. to be compliant.

The minimum zipline standards have required a 3:1 FoS for decades, and this is confusing to most operators who think the standards only require two brakes. The confusion starts because the standards say the FoS minimum for a zipline is 3:1, but they only require a primary and secondary or a fail-safe zipline brake, or 2:1. This discrepancy adds to the extremely high zipline accident rates because ziplines need three brakes; to follow the standards!

In 2002, Park City Mountain Resort (PCMR) set the zipline standard for trolley braking with a 3:1 engineering factor of safety (FoS). We built their RST-02, which incorporated two brakes, and had an emergency brake—a sixty-foot-long compression spring array—at the end. Twenty-one years later, the PCMR zipline is still accident-free because RST systems are fail-safe-safe (3:1).

Most owners and builders think gravity has primary braking reliability. That is false! Gravity braking is never safe for ziplines because steel cables expand and contract, and the weight of zipliners changes. They must consider all the ziplining variables: the participant's mass (m), trolley friction, and outside temperature. These all affect arrival speed. Gravity (g) accelerates all zipliners downward at -9.8 meters per second (m/s); wind resistance is always present, but zipliners stop because of their upward travel. Due to physics, the heavier a zipliner is, the faster they travel upward, not downward; gravity is a constant for all falling objects.

Steel bridges, unlike ziplines, have expansion joints that allow steel to expand and contract without buckling due to outside temperature changes; zipline cables cannot have expansion joints—the cable would fall—so ziplines expand and contract, which increases or reduces the bottom curvature (the belly of the cable). Ziplines change all day, so controlling a zipliner's speed is difficult, especially when using free-wheeling trolleys. Heavy participants are in the greatest danger on ziplines, and adding colder temperatures has been disastrous. My zipline expert witness thrives because most ziplines utilize two-wheeled trolleys. Another two-wheeled trolley problem is retrievals; when temperatures go up, the small/lightweight zipliners stop too soon, slowing the progress and costing the zipline owner valuable time.

Zipline Accidents

In 2016, I co-authored "Zipline Injuries on the Rise" with Rex Bush, Esq., published on hg.org and in Utah Trial Journal (2017). The article said that zipline injuries were increasing, and a Granite Insurance–North Carolina presentation validated the article at the 2020 virtual Association for Challenge Course Technology (ACCT) Conference and Expo. They told participants that 6 to 7 of every 100,000 zipliners were seriously injured, and over half were from zipline braking failures. These numbers are incredibly high when comparing ziplines to other amusement park rides; a rider's risk of injury on a roller coaster is one for every 700,000 riders.

As a zipline expert witness, I knew accidents were increasing; my investigations led directly to the invention of the 3-lb. RST in 2017. We have five new RST patents today because our 25-lb. PCMR trolleys are too heavy. We also know most zipline platforms are small, so a 60-foot spring array is unrealistic.

Our zipline systems are service-proven and fail-safe-safe with a 3:1 FoS; telescoping springs add safety and reassurance. If your zipline has two brakes, adding a third brake—creating a 3:1 FoS—reduces accidents, and you become compliant with all zipline standards.

Not all ziplines have 3:1 FoS for braking; most ziplines use two brakes (2:1) because the standards are misleading. For instance, ASTM F2959 says a zipline brake must be fail-safe (2:1), and the ACCT only requires a primary and secondary brake (2:1). Zipline accidents increase because of this confusion; most zipline builders fail to realize that three brakes, not two, follow the standard. Reliance on inadequate two-brake systems has led to skyrocketing accidents.

To mitigate injuries, our company Momentum Engineering, a DBA of ZipSafe, LLC, only sells service–proven, fail-safe-safe zipline systems with at least a 3:1 FoS. Our three brake ziplines keep all participants safe because being fail-safe-safe would have stopped this multi-million dollar settlement. We maximize your safety with every product we design and go beyond the minimum safety standards. We continue to develop more fail-safe-safe zipline braking systems, and our five US patents, three in the last three years, stop accidents.

If your system has a 2:1 FoS, we hope you follow the braking standards and add another brake to slow your zipliners and decrease my zipline expert witness engagements (ten investigations annually). Mention this narrative when you place your order on www.zipsafe.org or call us directly to receive a 15% discount on products and services.