Zipline Standards and Braking Trolleys

                                Controlled braking Zip Line 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 giant zipline we built in 2002 at Park City (Utah) 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 controlled-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.

AA Machining & Welding, Inc. was the parent company of Momentum Engineering in 2015, and in 2020 to move forward with testing zipline trolleys with controlled-braking—our seventh-generation RST—is a 2-lb. (mini) trolley that controls the speed of all zipliners in one setting. Assessing the RST-23 (mini) began soon after the IAAPA (International Association of Amusement Park Attractions) Expo.

Last summer we assessed our RST-22 and it performed flawlessly; the braking trolley safely stopped test-weights of 35—315 pounds on a 10-degree slope; we found that pin/slope setting #8 was ideal (for the rider weights) and the RST still had five braking locations to move closer to the wheel—less braking force. So, we shipped two RST-22 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 one hundred 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. The RST-22 were returned for a full refund, and we sent them the RST-23FS (see Image 1; red arrow).  

The Richardson Safety Trolley rests on a zipline cable (see blue arrow) reducing the water factor. The vertical lever arms with circular handles identify the #5  pin setting. Notice that the participant's carabiner (see purple arrow) connects below the handles acting as a lever arm 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 close to the wheel, #2, and #14 is the slowest and closest to the RST brake.

 ​The advantage of RSTs over uncontrolled trolleys (two wheels) that traverse ziplines at ninety-five percent gravity (9.0 m/s). Our RSTs have slope adjusting speed control—via pin/slope settings—to equalize zipliners to control the speed for all weights in one setting for a determined slope. We compared the Petzl® two-wheel trolley to the RST in this video. The zipline slope is 10-degrees. The video the Petzl uncontrolled trolley arriving a 22-MPH, and our RST-22 arrives at 2-MPH. Zipline owners and designers can establish a pin setting that stops an 80-lb. rider safely—on the same slope—as a 250-lb. rider. Each zipliner applies controlled braking using friction and their weight (mass) to stop them safely. Notice in this 2019 RST video using the same pin/slope setting to stop all weights and established a benchmark to reduce RST rollback. Patron retrievals occur daily with two-wheeled uncontrolled 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, and meet the standards when properly tested and they can eliminate braking related lawsuits.

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, this confuses most operators who think the standards require two brakes. The confusion starts when the standards say there is a 3:1 FoS minimum for ziplines, but they say we require a primary and secondary or a fail-safe zipline brake, meaning 2:1. This discrepancy adds to the extremely high zipline accident rates, because ziplines need three brakes, to remove braking related injuries from being number one cause.

In 2002, Park City Mountain Resort (PCMR) set the zipline standard for trolley braking with a 3:1 engineering factor of safety (FoS) for zipline braking. 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 is braking reliability. That is false! Gravity braking is never safe, and the accident rates prove it. Ziplines are not like steel bridges that expansion joints. The variables that are hard to control are zipline cables expand and contract, and the changing weights of zipliners; zipline builders 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 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 us that six to seven patrons settle lawsuits per 100,000 zipliners, and over half were from zipline braking failures. These numbers are incredibly high compared to other amusement park rides. For instance, roller coaster injuries are one for every 700,000 riders.

As a zipline expert witness, I know accidents are increasing; my investigations led to invent a 3-lb. RST in 2017. We have five new RST patents after our 25-lb. PCMR controlled braking trolleys. We also know most zipline platforms are small—shorter than ten feet—so a 60-foot spring array is unrealistic. Our zipline spring 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 or call us directly to receive a 15% discount on products and services.   

2002 Park City Mountain Resort Zipline

22-years ago, our company built a zipline for Park City Mountain Resort (PCMR) set to debut at the 2002 Winter Olympics. PCMR contracted Mr. Richardson's company (AA Machining & Welding, Inc. (Utah Government Steel Contractor) to develop a safer zipline braking system for the resort; see his patented passive braking technology.

Lake George, New York

Steep Ziplines need autobraking (friction based) trolleys and a properly designed spring array. This New York Zipline's (in the photos) has a 30-degree slope. Stopping zipliners proved dangerous with their magnetic braking trolleys.

30-degree Slope at Lake George, New York

The top of this zipline is seen near the top of the mound. Notice where the trees (near the middle) are cleared.

Steep Ziplines need autobraking (friction based) trolleys and a properly designed spring array. This New York Zipline's (in the photos) has a 30-degree slope. Stopping zipliners proved dangerous with their magnetic braking trolleys.

Dual Braking Zipline Spring Arrays

Tested in 2021 at American Adventure Park Systems in Georgia (see full video).

Testing Dual Zipline Spring System w/ Sandbags

All spring arrays need to be tested; always document testing and training.

See Video

Utah Ski Resorts

Most Utah Ski Resorts utilize spring arrays and auto braking zipline trolleys from the original trolley design at Park City Mountain Resort.