Keeping safe distances: The vital two‑second rule for the drivers

We frequently hit the road for family trips, which contributes to increased traffic on roads, including motorways and expressways. In such conditions, the rule of two — and in some cases even three — seconds of separation is crucial.

Despite attempts to enforce this rule through regulations regarding maintaining appropriate separation, it remains challenging to follow. This is partly because it does not apply during overtaking, which can cause confusion on the roads. Experienced drivers, however, are well-acquainted with the two-second rule, and older drivers often adhere to the three-second rule as well.

The rule is easy to remember: maintain at least a two-second gap from the vehicle in front of you while driving. In practice, this means that when you pass a post that another car has passed before you, you should go past it only after two, and preferably three, seconds.

Research by the Massachusetts Institute of Technology confirms the effectiveness of this rule. The study aimed to analyse drivers' capabilities in the context of autonomous driving systems. It found that drivers over 55 needed an average of 403 milliseconds to notice a threat and 605 milliseconds to decide. For comparison, drivers aged 20 to 25 recorded these times at 220 and 388 milliseconds, respectively.

This means that younger drivers have a reaction time of 0.6 seconds, including an additional 0.1–0.2 seconds for the reaction. On the other hand, older drivers need about 1.5 seconds for a full reaction. Additionally, activating the braking system takes around 0.3 seconds.

As the Road Traffic Act prescribes, the time-based rule is easier to apply than the distance in metres. Regulations require maintaining a distance equal to half the current speed (at 75 mph, this is 38 yards). Watching the roadside posts and counting the time passing them is much more convenient.

This issue is particularly significant, as failing to maintain an appropriate gap is the fourth most common cause of road accidents. Accidents outside built-up areas are the most tragic – in one in five, a person dies, whereas in built-up areas – in one in fifteen.