Speed is gravity sideways: A way to look at speed differently to understand its impact on young riders

By Ron Humphries | Contributing Columnist

Editor's note: North Carolina has adopting a new three-class system for electric-assisted bicycles under Session Law 2026-46 (HB 1094), which takes effect on December 1, 2026.  Under the updated law, compliant e-bikes are permitted on public roadways, bicycle lanes, and multiuse paths. Cities, counties, and the Department of Natural and Cultural Resources retain the authority to restrict specific classes on certain multiuse paths, greenways, or sidewalks. General natural-surface trails do not automatically grant e-bike access.

Opinion – I’m a retired NCDOT DDC engineer, and over the years I've worked alongside the NCSHP on several highway fatality accident scene investigations.

That work taught me an unforgettable lesson: kinetic energy has no conscience. It doesn't care if a rider is a careful kid, a good driver, or just someone having fun on a beautiful afternoon. When a vehicle stops suddenly, the laws of physics take over—and that energy must go somewhere.

A friend recently shared a tragic news story about a young rider who lost his life on a high-powered e-bike, and it reminded me of that lesson.

The bikes kids ride today can look a lot like the ones we grew up with. The difference is what they can do. Some modern e-bikes, 4-wheelers, and dirt bikes can reach 30, 40, even 50 mph. That’s highway speed, on a vehicle with no steel frame around the rider, no seatbelt, and no airbag; none of the things that we as a nation spent so much time incorporating into cars to give people a chance in a crash.

In highway fatality investigations, a lot of time is spent on the question: where did the energy go, and what absorbed it? In a car with highly engineered crumple zones, the vehicle itself burns much of it. On two wheels, there’s almost nothing between the rider and whatever they hit.

Looking through a physics lens can clarify it. Take a 100-pound, 13-year-old rider, for example. At 43 mph, that rider carries about 6,187 ft-lb of kinetic energy. To help understand ft-lb, think of dropping a 1-pound book onto your foot from a height of 1 foot. That impact delivers 1 ft-lb of energy. Stopping suddenly at that speed, hitting a tree or a concrete pole, for instance, involves roughly the same energy as falling from about 62 feet, or roughly six stories, onto pavement.

It helps me to think of speed as gravity, turned sideways.

The following calculation results are eye-opening and, hopefully, help you visualize kinetic energy.

- At 25 mph, the equivalent fall is about 21 feet, or about two stories

- At 30 mph, about 30 feet, or about three stories

- At 35 mph, about 41 feet, or about four stories

- At 43 mph, about 62 feet, or about six stories

Those story heights are approximate, about 10 feet per story, but the pattern is what matters. A jump from 25 to 43 mph doesn’t just feel a little faster. The energy more than doubles.

I’m not sharing this to judge anyone. We all care deeply about children's well-being, but I think most of us are still catching up to this new technology. The bikes got faster before our habits and our conversations could catch up.

Over the years, I've found it useful to treat safety concerns as teachable moments and things to check together. Many of these bikes have a speed setting in the manufacturer’s app, and it’s worth taking a minute to look at it with your child or grandchild; not as a gotcha, but as a “let’s see what this is actually set to” moment. A properly fitting helmet matters, too, and it should get the same attention as a car’s seatbelt.

Most of all, it helps to talk about what speed really means. Kids understand height tangibly, unlike miles per hour, which doesn’t always register. “Would you stand on the edge of a six-story roof?” is a question most of us would answer instantly. Connecting that feeling to a speedometer reading can make the abstract suddenly concrete, without turning it into a lecture.

I want kids to ride and have fun safely. I want them away from screens and playing outside, exploring the neighborhood and the countryside, the way we did. I want us to go into it with our eyes open, knowing that these machines carry more energy than they appear to.

Technology is moving fast. But our safety habits can catch up; let’s work together to make it happen, without pointing fingers.

Ron Humphries is a retired NCDOT Division Design Engineer and a Professional Land Surveyor (Retired). He has over 20 years of experience serving on City of Kings Mountain Planning and Zoning Boards and Boards of Adjustment.