In my state, the Victorian road rules section 126 state that there must be sufficient distancing so that a following vehicle can stop in time to avoid a collision with a vehicle in front in the event of a braking event.
So, the starting point is to assume the driver behind is the one at fault.
However, no attempt is made to define sufficient distancing.
But crucially, no definition is made to define what is an emergency braking event, which would be something more severe than a normal braking event.
Is it something obvious that a dashcam would show?
Is it perhaps because the driver in front decided they would miss a turnoff they saw perhaps at the last minute and had to slam on the brakes to slow down or miss it?
Is it because an AEB system triggered for no obvious reason?
Is it that the driver in front somehow decided they were annoyed and decided to play silly games?
Like all fuzzy road rules, section 126 is open to interpretation based on each circumstance.
The rule, in full.
ā126 Keeping a safe distance behind vehicles
A driver must drive a sufficient distance behind
a vehicle travelling in front of the driver so the
driver can, if necessary, stop safely to avoid a
collision with the vehicle.ā
Back in uni, circa the late 1960ās I became a certified driving instructor for US high schools. During the class there were many experiments designed to show things, including reaction time and stopping distances. One of us always proved the official numbers were designed for the inattentive and of ordinary skills, and a larger number were behind the curve.
My Renault always shows when I am within ā2 seconds distanceā of the vehicle in front of me, speed dependent, supposedly being reaction and stopping time. In adaptive cruise it will stay that far behind another vehicle.
The two second rule seems to be a good rule of thumb. Assuming you can calculate how far that is in distance based on current speed.
Does your adaptive cruise control adjust the distance based on conditions?
Wet road, fog, rain, gravel road, driver reaction times?
It gives an indication of suitable following distances and indicates as as start the 2 second and 4 second āruleā.
In the end it is up to the driver to ensure that suitable following distance is given so that an accident in the prevailing conditions is avoided. At times 4 seconds may not be an appropriate separationā¦a example is on snow covered roads where one may wait until the vehicle in front is a long way in front (e.g. off the down slope section) before proceedingā¦as there could be a risk the vehicle in front stops with your own vehicle sliding into the vehicle.
A term often used by the road authorities is ādrive to the conditionsā.
It is silent as there isnāt any standard metric which can be used. The appropriate metric is if someone stops suddenly in front of you and you stop safely, you have driven at a suitable following distance. This distance will vary as outlined above.
Accelerator and brakes as required. If a car cuts in front and the 2 seconds disappears suddenly, it will get off the accelerator but as long as the distance does not close further it will not brake but will drop back at a reasonable rate. It has a control that is useful in city traffic to keep closer, or when necessary on the highways. If the car cuts in front and we are closing on it, the AC will brake, and the quicker we close the harder it will brake to keep distance.
It also speeds up and slows down to keep a constant distance from a car in front that is not keeping a constant speed.
I am especially impressed with how well the AC ādrivesā in traffic (min 40 kph to stay engaged) and the only issue I have yet encountered was
How do you take into account individual driver reaction times? I found many different times on the web from 0.2sec for a F1 drivers typical response time for the starting sequence on the grid (an anticipated event prejudged by the timing of the lights) through to more than 2 seconds for average motorists. One source suggested that motor accident investigators may use 1.5 seconds.
Some of us have great trained/automatic reactions and some of us not so good. Apparently.
If your question includes my AC, I THINK it is 2 seconds because that was what the salesman said. It is a respectful physical distance that is more or less distance, depending on speed (and the control to reduce it for traffic conditions).
The 2 second rule of thumb often quoted isnāt reaction time per say, it also includes ability to respond appropriately to stop or avoid a collision. It caters for different car types (inc performances of tyres and braking systems) as well as the fraction of a second reaction time of the driverā¦as well as determining and able to take the necessary course of action. If one knows ability to stop/respond is compromised (eg. loaded vehicle or towing), then the 2 second could be 3 or 4 or more.
It isnāt a vibe but driving to the conditions. If one wants to nominate a safe following distance, how long is a piece of string. If one only uses a distance (say 20m) or time (say 2 seconds), there will be many times such wonāt be sufficient.
In some ways it is like speed limits. These limits arenāt what one can safely drive at all times. If one does, it is sure way to become a statistic. It is a maximum legal speed under good conditions. Under fog, black ice, surface pooling water etc, driving at the maximum posted speed limit can be very dangerous.
And earn you a ticket for āDriving without due care and attentionā or even to the possibility of āDangerous drivingā in some cases. Speed limits are not always a safe speed nor always a defence in Court.
