Driving in Poor Weather
I’ve posted a few threads on the forums recently as we’ve had some really poor weather here in the Great White North as of late. Blizzards, heavy snow, icy roads, we’ve been through it all in the last few weeks. Fog, heavy rain, snow, sleet, hail, strong winds, bad weather for driving comes in all forms…and it comes on when we’re out on the road. There’s a common problem many of us Canadians, and those in the Northern USA see every year - people seem to forget all of the winter driving skills they used last year. The first bit of bad weather brings oodles of fender benders and serious collisions alike.
What to do – continue on or pull over? Stay home or make the trip we planned? These are decisions we each have to make at the time.
The simple answer is I can’t tell you to go or stay home. I can tell you a few tips to use if you do venture out on the roads when the weather is bad however.
Slow Down. This is the biggest one. The physics of driving in bad weather revolves around the reduced “coefficient of friction”the tires are able to produce. Coefficient of friction, in my world represented by the Greek letter µ (pronounced “mew”). This is a numerical value that represents the amount of force the tires are able to generate as a percentage of gravity. For example, an average car on dry asphalt might be able to generate a µ of 0.70. One on ice may be µ = 0.35. What that means in the real world is that your distance required to stop from any given speed has just doubled.
Leave more space when following another vehicle. Common sense right? If your stopping distance has doubled, so should your following distance. More space gives you more time to react, and more of a chance of avoiding something disastrous. I’ll go out on a limb and say that a huge majority (maybe like 90%) of people driving on an average urban freeway are following too close everyday they drive. Anyone remember what your driver training said to use as a following distance? I didn’t think so 
It’s actually 3 seconds in ideal conditions. I’d suggest RVers use 4 seconds due to the increased weight we haul around when we travel. The way to measure this is as follows:
- Watch the vehicle in front of you pass a reference object. This can be a mark on the road, a light post, a shadow, almost anything.
- Count in the following manner: “One thousand one, one thousand two, one thousand three…”
- When you reach three, you should just be passing the reference mark.
- If you reach it before you reach three, you’re too close.
For less than ideal conditions, the distance should be increased.
I’ve seen 60, 70, 80 car pile-ups on the news recently. People driving too fast when they can’t see. They are out driving their ability to see. The typical following distance we all see of 3, 2, or even 1 car-length behind another vehicle is a collision waiting to happen. Sure 99.9% of the time, that guy in front will keep moving right along, but at that moment he/she has to brake suddenly, the best driver in the world won’t be able to slow in time to avoid a collision. I’ve spoken before about the perception/reaction time in the blog called “STOP” (http://blog.rv.net/2008/01/21/stop/). The math shows that the vehicle following will not even have a chance to slow before the collision.
There is a little known theory that poor visibility actually causes some drivers to speed up instead of slowing. The theory goes that poor visibility removes the normal visual cues we all use to judge our speed (excluding the speedometer of course), and speeds creep up.
Keep your vehicles lights clean. These are the biggest safety features on your vehicle in poor weather. Being able to see and being seen are the best things you can achieve. Don’t let road spray, snow or frost build up on your headlights or tail lights. If you’re having to clean your windshield often, your light lenses are also getting just as dirty. The engineers that design the lamps on your vehicle/RV have to meet certain visibility and light output specifications, and when the lenses are dirty, they no longer function as they should.
Keep your lamps the factory color. Aftermarket tail lights, tail light covers, tinted headlight covers, and other commonly sold dress-up accessories seem harmless, but they can dramatically reduce light output. Other drivers can also be confused when they see green tail lights for example in a snow storm. I know RVers aren’t big into this, but you may have kids that are. LED tail lights are great. They react fast to the brake pedal, and they are bright and the right color, but they drawback they have is that they don’t create heat. The tail lights on a tractor/trailer would normally melt snow due to the heat they produce, now they get covered with snow and stay that way. If you have LED tail lights, you’ll have to be more diligent at cleaning them.
If you do have to pull over and stop due to poor driving conditions, pull way off the road, not just over to the shoulder. It is best to get to an intersection or side road, and get well off the road. You would not want to be struck by a vehicle that may wander onto the shoulder.
I know some may disagree, but I say you should not drive with your hazard lights on in poor weather. To me – hazard lights are for a stopped vehicle, or to use if you have to crawl up a hill in good weather. It may confuse some drivers.
If you don’t have to be out in poor weather, stay home. If you must travel, for your sake and mine, do it carefully.
One more thing, if your State or Province does not have a law that says you have to slow down when passing an emergency vehicle on the side of the road with its flashing emergency lights in operation, do it anyway. Those of us that have to stand on the side of the road as cars whiz by appreciate the ones that slow down and move over.
See you next week, comments welcome!
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Light Truck and motorhome tires are not as large (tread contact patch) in proportion to the loads placed on them, and to make them wear well and have low rolling resistance are made with harder rubber compounds than automobile tires. These do not have as good adhesion as typical automobile tires, so no matter how good the brakes are the vehicle will take longer to stop, especially on dry roads.
On wet or snowy roads the difference is not as great, and the higher contact patch pressure reduces the tendency of the tire to “ride up” on the water (hydroplane) or snow. So contact with the pavement is maintained better – on snow, up to the point where the snow packs and holds the tire tread off the pavement.
On ice nothing sticks very well except special rally racing “hydrophilic” tires, which as far as I know are not to be had in LT or motorhome tire sizes. Ice is slipperiest just below the freezing point, for the pressure of the tire on the ice melts the ice in a thin film, creating a quite effective lubricant between the tire and the ice.
Studs are not nearly as effective as commonly thought. They work well only on hard ice. The studs themselves are slippery on pavement, detracting from the adhesion the same tire would have without studs installed. They are also illegal in many jurisdictions during part or all the year. How can you have your studded tires exchanged for non-studded tires in the middle of a trip? Only by having the studs pulled out (and discarded). Further, they ruin the roads. I-90 in eastern Washington has deep troughs worn in the concrete in the tire tracks!
Snow tires are good for…snow (and mud). They have much less rubber in contact with a dry or wet road surface than a regular highway tread tire.
“All-Weather” tires are a compromise between snow tires and warm-weather road tires. They have a more open tread than regular highway tires and more rubber on the road than snow tires.
As always, for the best traction on snow or ice, chains do the best job. Cable “chains” are easiest to install and the least rough riding. They do not grip nearly as well as real chains, but may be enough. Cross-link chains do a good job. Cross-link chains with twist-bar “teeth” bite even more effectively. Diagonal cross chains provide better side ways grip against side slipping but somewhat less straight-line grip.
It is worth mentining that HID headlights have the same issues as LED taillights regarding heat and icing . They do ne generate enough heat to melt frost and ice either. I have them on a car and must clean them off in the morning if they are frosted.