Just for a moment imagine with me that you’re cruising south on Nellis Boulevard in the middle of Las Vegas. Makes me nervous just thinking about it. Maybe you’ve been there. If not, it might help to Google a Vegas map so you can follow me on this.
You left Grand Junction, Colo., at 8 this morning and you’ve been driving for 10 hours. You heard that you can get off the Interstate and use Nellis as a short cut to the RV park on Boulder Highway, where you’ll park the rig and get a good night’s sleep. It’s your first trip to Vegas and you and the family have big plans for the next few days.
Nellis is a very busy, six-lane, main north-south artery through Las Vegas with a lot of signal-controlled intersections. You know the kind. There’s at least one Nellis Boulevard in every big city. I’m not sure why but the speed limit on this street is 40 mph which of course makes everybody go at least 50. You know how that goes.
You stay in the right lane like you’re supposed to and you’re doing a pretty good job staying with the flow of traffic but you keep looking ahead and wondering, “When the signal changes at that next intersection, will I be able to stop this thing before I drive into the intersection and get smacked?” Your palms start sweating and your mouth goes dry. You know as well as I do . . . it’s a crapshoot! But it helps to have a really good understanding of what’s going on here.
Two principal forces are at work on any vehicle when it’s in motion: gravity and energy of motion. We all know that gravity is what makes us lose speed when we’re going uphill and what makes us gain speed when we’re going downhill. We know that most vehicles are built with a low center of gravity so they will be stable in turns, curves and during quick maneuvers.
But we may not be quite as well acquainted with energy of motion, also called kinetic energy, and the profound effects it has on a vehicle in motion, especially the larger and heavier vehicles that we drive. I don’t know about you, but we wrestle with a 32-foot motor home with a car in tow and total weight of about seven and a half tons! Once we put that much weight in motion, energy of motion is something I want to know about and keep in mind.
Two things determine energy of motion. Weight and speed. Trouble is those two things don’t affect stopping distance the same way. If you double the WEIGHT of a vehicle you just double its stopping distance but if you double the SPEED of the same vehicle it takes four times more distance to stop. Triple your speed and the vehicle needs nine times the distance to stop. See where we’re going here? And if conditions are not ideal, i.e. driver not fully alert, bad weather, brakes or tires less than good, you can add even more stopping distance — a lot more!
In ideal conditions (by that I mean the average driver reaction time of 3/4 second, with brakes and tires in good condition and stopping on dry, level concrete pavement) total stopping distance for a 3,000 pound automobile traveling at 45 mph will be approximately 150 feet. That’s half the length of a football field. At just 45 mph! Imagine what it is for your big, heavy vehicle.
Here’s something else to think about. There’s a lot more to stopping than just hitting the brakes and stopping. Total stopping distance has three components:
- Perception time and distance
- Reaction time and distance
- Braking time and distance.
Perception distance can vary a lot depending on the nature of the hazard, your ability to identify the hazard and your visibility. Reaction distance can vary according to driver condition and the complexity of the situation. Braking distance we’ve already talked about.
So let’s take another look at Nellis Boulevard, or pick a street you like. You’re driving your motorhome or towing your fifth wheel. Your speed is 40 mph, it’s daytime, you’re alert, your brakes and tires are in good condition. You’re approaching another one of those signal-controlled intersections.
You get to within about two hundred feet of that intersection and, boom! The signal goes to yellow. You know the yellow light means you should make every reasonable effort to stop. Do you brake and hope you can stop before you enter the intersection and get smacked? Or, do you hit the gas, run the red light and still get smacked? No wonder your palms are sweating.
Next time you drag out the old RV give yourself an extra day to get ready. Take your rig out to a safe place and calculate your stopping distances at different speeds. There’s a massively huge parking lot at a horse race track not far from where I live. That’s where I do my testing.
“It surrounds us and penetrates us. It binds the galaxy together” – Obi-Wan Kenobi in A New Hope.
MAY THE FORCE BE WITH YOU!