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Behind-the-Wheel

Skid marks tell a story

Tire marks left on the pavement at a collision scene tell the investigator many things about the events involved in a motor-vehicle collision.

One common example involves using the length of the mark to calculate pre-collision speed. It was often an interesting exercise that could either verify or call into question information given by witnesses and drivers.

Following my training course, the first opportunity I had to try this out involved an intersection collision. A driver had turned left in front of a taxi. The taxi driver had slammed on the brakes, but was unable to avoid hitting the left-turning vehicle.

The taxi driver assured me that he had been travelling at the speed limit pre-crash.

I got out my calculator and measuring tape. The calculated speed was over the speed limit and, as there was a crash, some of the speed of the taxi did not contribute to the length of the skid marks.

When I told the taxi driver what I had just done and asked again how fast he was going, he hung his head and said that it was a bit over the limit.

Even more interesting was the opportunity to teach it to a class of physics students at a Qualicum Beach high school.

My supervisor and I started the class by deriving the slide-to-stop formula from the basic equations the students were learning.

Simply put, the speed of the vehicle is equal to 15.9 times the square root of the skid distance multiplied by the co-efficient of friction for the road surface.

This applies to a level surface and will work for both ABS and non-ABS braking systems.

Next, we went to the parking lot where I readied the shot marker on my police vehicle and had one student sit in the passenger seat to verify the speed by watching the radar display.

After reaching 50 km/h, I braked to create the skid and the shot marker fired a piece of blackboard chalk onto the ground when the brakes were applied. By measuring the distance from the chalk mark to the shot marker at the other end, the exact skid distance was known.

The shot marker is important for accurate distance measurement as the tires take a bit of time to generate enough heat between themselves and the pavement to leave a mark.

Some braking is done before the beginning of the visible skid mark, so these speed calculations always underestimate the initial speed slightly.

My supervisor led the others through the use of a drag sled, which is essentially a section of tire weighted with lead or concrete inside.

Weighing it and then measuring the force required to slide it over the pavement allowed the students to calculate the co-efficient of friction for the road surface.

Back in the classroom, we used the formula, the skid distance and the co-efficient of friction to calculate the police vehicle's initial speed when the brakes were applied. The answer was exactly the speed shown on the radar.

While real world collisions are often much more complicated, this was a great opportunity to show the students an application of what they were studying in a manner that they had not considered.

This is the process that was used to teach that section of my collision investigation course and one that is repeated time and again with varying circumstances on testing days.

Testing days allow the investigator to gain experience with known data and satisfy the courts of the accuracy of speed calculations undertaken.

Story URL: https://www.drivesmartbc.ca/police/speed-skidmarks



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Get the light out of my eyes

Glaring fog lights

One of the most common complaints I hear that is not about a moving violation concerns the use or misuse of lights on vehicles.

Here is one of them:

  • "What is really starting to annoy myself and many others is people driving with their fog lights on during clear nights or even during the day. Is this not an infraction? These lamps are often unreasonably bright."

I agree with this reader. I also find many fog lamps unreasonably bright, even during the daytime. What's to be done about it?

The following information may help you to use these lights effectively and avoid causing problems for others.

First, let's be sure we are all on the same page. Fog lamps are identified by the SAE F marking on the lens, or a B above the circle with the E in it on European lamps. In B.C. you are allowed two fog lamps that emit either white or amber light.

They must be mounted on the front of the vehicle, below the headlamps, but not more than 30 cm below. When you switch them on, the parking lamps, tail lamps, licence plate lamp and, if required, clearance lamps must also illuminate.

Fog lamps may be used in place of headlamps if atmospheric conditions make the use of headlamps disadvantageous. Otherwise, fog lamps may be used at any time of the day or night and, in fact, are used as the daytime running lamps on some vehicles.

Vehicle lighting at the time of a vehicle's manufacture is regulated by Transport Canada. Specifically, Technical Standards Document 108, which details construction, performance and location of lamps and reflectors.

Here in British Columbia, lighting use and maintenance is regulated in Division 4 of the Motor Vehicle Act Regulations.

Essentially, it requires that the lights and reflectors that a vehicle was manufactured with must still be there and function as originally intended. Dimming of headlights and the times that vehicle lights must be used are also set out here.

I suspect that the unreasonable brightness comes from improper aim. Fog lamps must be adjusted and aimed so that, at a distance of eight metres from the lamp, the centre of the beam is at least 10 centimetres below the height of the fog lamp.

Oddly enough, there is no tolerance specified as too low, but anything higher than horizontal is too high.

There are other reasons that could contribute to problems. The use of LED replacement bulbs in housings designed for filament bulbs is one of them, along with using higher wattage filament bulbs than is intended.

The Ministry of Transportation and Infrastructure publishes an inspection and approval protocol for vehicle lighting to help inspection facilities decide what to pass.

It is a good guide to follow if you are considering making modifications to your vehicle's lighting system.

Scott Marshall from Young Drivers of Canada has some good tips on using your vehicle's lights and fog lights when the weather is bad in this video: https://youtu.be/vg9FDZxERgs

Toyota adds this video about using rear fog lights: https://youtu.be/SnNDNnVFCFQ

Story URL: https://www.drivesmartbc.ca/equipment/glaring-fog-lamps



Keep your windows clear

I received yet another great topic suggestion, and one that is timely for another reason entirely.

“I carry a Handicap parking permit. When I was first issued this permit an outline of my responsibilities said that I was to remove it from the rear view mirror while driving "...as it is against the law to drive with the permit hanging (obstructed vision)."

“I see often see permit holders driving with their permits hanging from the rear view mirror, so this rule is obviously not being enforced. A mention in your column may help remind drivers of their legal responsibility in this regard.”

Fully 80% of the information that we need to drive safely comes through our eyes. Anything that keeps that information from reaching us is a concern.

The law says that you must not move your vehicle on a highway when the driver's view to the front or to the sides is obstructed. Obstructions may range from the parking permit or other object dangling from the rearview mirror that this reader mentions.

Driving with only a small spot of frost scraped away or removed by the defrosters is what came to my mind as I always found drivers peeking through the small half circle of glass cleared by the defrosters during the first few frosts of the year.

Receiving a ticket and then having to scrape or wait before continuing is not a good way to start the day.

A traffic ticket for a violation of section 195(1)(b) MVA costs $109 and three penalty points.

I have the luxury of parking my vehicle in my garage, so I don't have to scrape my windows at the beginning of my trip, but I may have to park outside at my destination.

Most of the time, I just use my snow brush and ice scraper to clean all the windows before I drive away, but with a little preparation, that task can be made quicker and easier.

Covering the windshield with anything that keeps moisture away from it will prevent frost from forming on the outside. A tarp, blanket, towel or even cardboard will help reduce the work.

There are commercial de-icing sprays, but you can save a significant amount of money by making your own.

Find a suitable spray bottle and fill it with a mixture of 2/3 70% isopropyl alcohol and 1/3 water. Spray it on, wait a few moments and all that scraping is no longer necessary.

Your spray can be stored in the vehicle as it will not freeze in most areas of our province.

While we are on the topic of vision and changes in the weather, this would be a great time to check some other vehicle components as well.

Is your windshield washer topped up with the correct cleaner, are your wiper blades supple and undamaged and is your scraper at hand?

One final mention is something that I learned while researching this topic. Leaving your windshield wipers pulled back from the windshield at the end of each trip will prevent damage to the wiping edge.

Your wipers will last longer and clean your windshield without streaks.

Better to be ready to cope than it is to take chances with your safety and the safety of those who have to share the road with you.

Story URL: https://www.drivesmartbc.ca/unsafe-driving-practices/driving-vision-obstructed



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Stay in your lane

Are some of us such sloppy drivers that we can't even stay between the lines on the highway?

I was driving home from work and met a pickup truck completely on my side of the double solid line in a set of winding curves.

Was the driver not paying attention or was he so intent on not slowing down that he straightened out the corners to avoid braking?

I suspect that it was the latter.

One of the first things that we learn when we drive is that we drive on the right half of a two-lane road and may only use the other half in limited circumstances.

These circumstances are defined by the law and do not include driver convenience as in situations like the one I described. Our trust that the other drivers will remain where they are supposed to be is central to using the highway safely.

The simplest road does not have any lines painted on it. The rule I mentioned in the last paragraph still applies, you must drive on your half unless it is not practical to do.

You will have to be able to justify that impracticality if you find yourself in traffic court disputing a ticket or civil court following a collision.

On most of our highways, road maintenance includes a fresh coat of paint on the lines. If it didn't matter what the lines meant there would only be one type of line, or no line at all.

You would be free to judge that you were in your own half of the highway. However, it does matter, and drivers must be aware of what the lines mean and follow their requirement.

On highways with multiple lanes for our direction of travel, we need to stay consistently within the lane that we have chosen to use.

Lines that you must obey may be on your left and on your right when you are driving, even when there is only one lane for each direction.

Believe it or not, that solid white line at the right edge of the roadway defines where you are supposed to drive. Keep to the left of it.

Here are some tips to help you maintain proper lane position:

  • Look well ahead at the centre of the lane that you are driving in
  • Keep your hands level on the steering wheel
  • Keep your grip on the steering wheel relaxed but grip tightly enough for control
  • Do not focus exclusively on the vehicle in front of you, keep your eyes moving
  • Do not focus on the edges of the road just in front of your vehicle
  • Establish reference points for the edges of the road in relation to the front of your vehicle when it is properly positioned
  • Maintain sufficient and equal tire pressure
  • Maintain proper wheel alignment for your vehicle

Are you confused? Drop by an ICBC Driver Service Centre and pick up a copy of Learn to Drive Smart for review, it's free.

You can also find your own electronic copy of the manual at www.icbc.com.

Story URL: https://www.drivesmartbc.ca/lanes/maintaining-proper-lane-position



More Behind the Wheel articles

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About the Author

Tim Schewe is a retired constable with many years of traffic law enforcement experience. He has been writing his column for most of the 20 years of his service in the RCMP.

The column was 'The Beat Goes On' in Fort St. John, 'Traffic Tips' in the South Okanagan and now 'Behind the Wheel' on Vancouver Island and here on Castanet.net.

Schewe retired from the force in January of 2006, but the column has become a habit, and continues.

To comment, please email

To learn more, visit DriveSmartBC



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The views expressed are strictly those of the author and not necessarily those of Castanet. Castanet does not warrant the contents.

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