Speed, safe distance and positioning on the road
What this domain tests
This domain tests speed limits, the tractor's own maximum, following distance, stopping distance and lane position. The exam expects you to distinguish the posted limit from a safe speed and to allow for the extra mass and length of a trailer.
Limits and safe speed
- General Danish limits are 50 km/h in built-up areas, 80 km/h outside built-up areas and 130 km/h on motorways, but local signs and conditions can lower them.
- A tractor is generally limited to 40 km/h by its construction and registration. The road limit does not raise that maximum.
- Drive at a speed from which you can stop within the distance you can see to be clear. Rain, mud, gravel, ice, a heavy load and a trailer all increase stopping distance.
- Keep a following distance of at least two seconds in good conditions. With a loaded trailer, poor visibility or a wet road, increase it substantially.
- Keep to the right-hand side of your lane and do not straddle lanes. If you are holding up a queue and can safely let traffic pass, do so.
Stopping distance
Total stopping distance is reaction distance plus braking distance. Reaction distance grows linearly with speed; braking distance grows with the square of speed. A combination at 40 km/h has about 11 m of reaction distance in one second and, on a dry road with reasonable grip, about 12-13 m of braking distance, so roughly 24 m total. At 80 km/h the braking distance is about four times as long.
Worked example
You drive a loaded tractor-trailer at 40 km/h on a dry farm road. Your reaction time is about one second. Reaction distance is 40 divided by 3.6, about 11 m. Using a braking coefficient of about 0.5, braking distance is roughly 12.6 m. Total stopping distance is about 24 m. If the road is wet, the braking distance increases, so the correct following gap is much more than 24 m. A two-second gap at 40 km/h is about 22 m; in rain, double it.
Traps that cost marks
- Treating the speed limit as a target rather than a maximum.
- Tailgating because the tractor can stop quickly; the trailer cannot.
- Forgetting that a loaded trailer lengthens stopping distance.
- Driving in the middle of the road on narrow rural roads.
- Failing to let a queue pass when it is safe to do so.