Adjust for bad weather or motorway

Home › Courses › Safety distance

Adapting your safety distance on the motorway and in bad weather: from the two-second rule to the four-second rule.

Cover, Adjust for bad weather or motorway

Lesson objectives

Understand why to double the safety distance in bad weather Apply the 2-second rule on motorway at 120 km/h and adapt it to conditions Calculate adjusted distances for rain, snow and ice

The 2-second rule: reminder and motorway application

On motorway, the 2-second rule remains the reference method, the exam bank explicitly states this for normal speed. At 120 km/h , it gives 60 m with the shortcut "speed ÷ 2", approximately 67 m if counting the two exact seconds. Verification on the road: identify a fixed point, pole, sign, bridge pier, and count two seconds after the vehicle ahead passes. If you reach the point before the count ends, you are too close.

Motorway in good weather, normal safety distance

Bad weather: double the distance

Adapt the count to the conditions: Wet ground : 3 seconds instead of 2, approximately +50% , 90 m at 120 km/h. Snow or ice : 4 seconds , which is double the base distance, at least 120 m at 120 km/h. So it is on snowy or icy ground that you double, not in rain.

Wet ground

Wet road after rain. Tire grip decreases, braking distance increases by 50%. At 120 km/h, go from 60 m to 90 m safety distance.

Calculation in rain at 120 km/h

Normal distance: 120 ÷ 2 = 60 m Add 50%: 60 × 0.5 = 30 m Total distance: 60 + 30 = 90 m Verification: Say "one crocodile, two crocodiles, three crocodiles", you must pass the fixed point after.

Motorway in rain, increased distance

Snow and ice: at least 4 seconds

On snowy or icy ground, grip is extremely reduced. Safety distance must be at least 4 seconds : "one crocodile, two crocodiles, three crocodiles, four crocodiles". At 120 km/h, this represents approximately 120 to 140 m , much more than double the normal distance. In these conditions, also reduce your speed if possible.

Black ice

Very thin layer of ice on the road, often invisible. Grip almost zero. Minimum safety distance: 4 seconds at 120 km/h.

Safety distances at 120 km/h according to conditions

Condition Counting At 120 km/h Ratio to base Dry ground 2 seconds 60 m (shortcut), ≈ 67 m exact reference Wet ground 3 seconds 90 m + 50% Snow or ice at least 4 seconds at least 120 m × 2

Tip for the exam and the road

At the exam: at 120 km/h, 60 m on dry ground, 90 m in rain, at least 120 m on snow or ice. The usual trap is to give 60 m when the statement mentions rain. On the road: count in seconds rather than meters, it is the only method that automatically adjusts to speed. And remember that article 10.1, 1° requires you to adjust your speed according to weather conditions and road conditions: on ice, lengthening the distance without easing off is not enough.

Common exam trap

Many candidates forget that safety distance depends on speed AND conditions . A question may ask for the distance in rain at 120 km/h: answer 90 m , not 60 m. The doubling (or adding 50%) is mandatory.

F5

F5, Start of motorway. From this sign, the special rules of article 21 apply: maximum speed of one hundred twenty kilometres per hour, but also minimum speed of seventy kilometres per hour on the entire roadway. Access is prohibited in particular to pedestrians, cycles, mopeds, vehicles unable to reach seventy kilometres per hour on level ground, agricultural vehicles and quadricycles without an enclosed cabin.

F7

F7, End of motorway. You are leaving the motorway. The specific motorway rules, in particular the speed limit of 120 kilometres per hour and restricted access, no longer apply. Adjust your speed to the new road and remain alert to the type of road you are joining.

A15

A15, Slippery road. The road may be particularly slippery in case of rain, ice, loose gravel or fallen leaves. Avoid sudden braking and sharp steering. Increase safety distances and adjust your speed to the conditions.

A17

A17, Loose gravel projection. The roadway has been recently resurfaced. Small stones may be thrown up by the wheels. Slow down to avoid damaging your windscreen and that of the vehicles following you. Keep a good distance.

Additional factors affecting stopping distance

Other factors besides weather lengthen the stopping distance, and they all act on the same link: the reaction time . Alcohol lengthens reaction time and impairs the assessment of distances and speeds; the effect increases with the level. Drugs and certain medications , the boxes bear a coloured pictogram, produce comparable effects, sometimes longer and less predictable. Fatigue , distraction and mobile phones do the rest: a two-second glance at a screen at 120 km/h means more than 65 metres travelled blind . The precise figures that appeared here, « 5 to 8 seconds » of reaction time under drugs, are not based on any verifiable source and have been removed. What the test assesses is the direction of the effect, not a specific value.

Before a long motorway journey

Check your tyres (wear, pressure), get plenty of rest, and avoid alcohol and medications that cause fatigue. In bad weather, slow down and increase your distance. It is better to arrive 10 minutes late than to risk an accident.

Key points to remember

Motorway, 120 km/h, dry road : 60 m (shortcut « ÷ 2 »), or 2 seconds. Wet road : 3 seconds, approximately 90 m , this is a +50 % , not a doubling. Snow or ice : at least 4 seconds, or at least 120 m , there, it is indeed double. Counting in seconds adjusts itself to speed; metres do not. Alcohol, drugs, medications, fatigue, mobile phone : all lengthen reaction time , and thus the entire stopping distance. Article 10.1, 1° : speed must be adjusted according to weather conditions, road conditions, visibility and traffic, lengthening the distance does not dispense with slowing down. Useful signals: A15 slippery road, A17 loose gravel projection.

Congratulations!

First do the quiz for this lesson to validate what you have learned, then practise on the exam simulator and the multiple choice questions . You have completed this entire course. Congratulations, now for the practical part!

BelgianLicenses

Each completed lesson brings you closer to your licence: keep going, you are really making progress.