Space management & following distance are key components to pass your road test, regardless of class - watch the video!
One of the competencies that you have to demonstrate on your road test is space management. Underpinning space management is following distance. Many students are somewhat confused or not quite clear on what following distance is or why we measure in time. So today we're not talking to you about following distance and how to determine that and why it's determined in time as opposed to distance and we'll get you ready for your road test.
In your road test for cars and light trucks you need to maintain the following distance of two seconds; for commercial vehicles it's closer to five seconds, especially the bigger the vehicle is. Obviously if you're in an ambulance it's going to be three to four seconds or a small bus. The size of the vehicle determines the following distance and as the vehicle gets bigger the greater the following distance. The way that we measure following distance is by time. We're following another vehicle - we look for a fixed object along the roadway. When that vehicle in front of us passes that fixed object we begin to count; one crocodile, two crocodiles. When we go past the same fixed object, that's when we stop counting. Whatever we got to - 2 crocodiles, 3 crocodiles, four crocodiles, or five crocodiles. That is the amount of distance that you are following the other vehicle in front of you. The reason that we measure in time as opposed to distance: saying you're following another vehicle at three car lengths is kinda like saying, "well how long is a piece of string?" We don't really know!
Why Following Distance is Measured in Time
We can determine however, if we measured by time exactly how far we are behind that vehicle. If you're traveling at a speed zone of 60 kilometers an hour you're traveling at approximately 17 m/s, therefore if you're maintaining a two-second following distance behind the vehicle in front of you - at sixty kilometers an hour you're at approximately 34 meters behind the vehicle in front of you. If you go out onto the highway and increase your speed to a hundred kilometers an hour - you're travelling distance is now 28 meters per second at a hundred kilometers an hour. So at a two second following distance your following distance is now 56 metres as opposed to 34 meters that you were doing 60 kilometers an hour. So what you can see is as the speed increases so does the distance between vehicles. This is now why we use time because the distance between the vehicles expands and contracts with increasing speeds. And speed is the most important factor in determining how fast a vehicle will stop. That is now why we measure following distance in time as opposed to distance.
In conclusion, for the purposes of a road test, you have to have space management. Underpinning space management is following distance because the space in front of your vehicle is the one space around your vehicle that you can always always always control. Two seconds for light trucks and cars, for commercial vehicles it's five seconds following distance. The one old rule that's still on the books: commercial vehicles following outside of an urban area can follow at two hundred feet. They still haven't taken that off the books but it still in the manuals if you look hard enough.