Valitse kieli:
Select Language:
Välj språket:
2.1 Car kinematics
Car kinematics
Cars' acceleration, steering and slowing down requires traction a.k.a. friction. Friction is generated, when gravity of earth pulls the tire towards the road surface. Contact area with tire and road surface is affected by accelerating force, braking force and centrifugal force caused by curving. An increase in any or all of these factors will decrease the amount of traction that the car will have. By decreasing a car's traction, you are thereby decreasing the amount of control you have over the vehicle. When the skidding increases the driver may lose the control of the vehicle.
The stopping distance consists of the reaction distance and the braking distance. Normal reaction time in traffic is 1-1.5 seconds. For example if a car moves 80 km/h it equals to 22 meters/second. The length of reaction distance depends on reaction time, and most of all, on the car speed. When the speed doubles also the reaction distance doubles. Braking distance is affected by the traction, the braking style and the speed of the car. When the speed doubles the braking distance and impact energy quadruple.
From this link you can compare the braking distances on different speeds and grips.
Safe driving of a vehicle
You must adjust the speed of your vehicle and its distance from the next road user to ensure safety, while taking account of road conditions, the weather, visibility, the amount and type of load on the vehicle, and other circumstances.
You must be able to control your vehicle under all conditions. You must be able to stop your vehicle on the clear road-section ahead of you and in all predictable situations.
The purpose of the speed limits is to decrease the accident risk of the road users and reduce the number of traffic accidents and casualties. Speed limits help to generate even traffic flow, which leads to decreased need for overtaking. Speed limits also help the flow of traverse and merging traffic, create a limit for situational speeds and improve predictability. The highest permitted driving speed in Finland is 120 km/h.
Speed limits specific to vehicle types as of June 1st 2020
100 km/h
Passenger car and van with a trailer weighing a maximum of 750 kg, and motorcycle.
Special vehicle with a curb weight of less than 0.8 tons.
Buses under certain conditions.
80 km/h
A combination of a passenger car or van and a trailer with an axle mass of more than 750 kg
Lorry
Bus
Special vehicle
B-category tractor with ABS and a design speed of more than 60 km/h
60 km/h
B-category tractor with a design speed of more than 40 km/h.
Snowmobile on a snowmobile trail.
50 km/h
Tractor registered for road use.
45 km/h
Moped with two or three wheels, and light quadricycle.
40 km/h
Vehicle with at least one axle with no suspension
Tractor
Off-road vehicle and self-propelled machinery
25 km/h
Low-power moped
20 km/h
Vehicle equipped with metal tracks