【Car Knowledge】How to judge the safe distance on highways
🚗 Editor's honest opinion: Hong Kong's highway safety distances aren't as long as you might think.
While speed limits on Hong Kong's expressways (such as Tolo Highway, Tuen Mun Highway, Tsing Sha Highway, and West Kowloon Highway) are generally 70–110 km/h, actual speeds often exceed the limit by 10–20 km/h. Furthermore, there are numerous exits and diversions. Many people shorten their lanes, thinking they're "leaning too far ahead of others," but then suddenly get into an accident when the car ahead brakes.
I once tried driving at 100km/h on Tolo Highway. Suddenly, a car cut in from the front and decelerated rapidly. I was too close at the time and had to use ABS to stop it. After that, I never dared to get too close.
📐 The core principle of safe distance
The safety distance refers to the total distance your car needs to travel from the time the driver sees the car in front slow down to the time it comes to a complete stop .
It consists of two parts:
- Reaction distance : The distance it takes for your brain to react and your foot to brake (approximately 0.75–1 second).
- Braking distance : The distance required for the vehicle to come to a complete stop after the braking system is activated.
🔢 The faster the speed, the distance added together increases exponentially , not simply by addition or subtraction.
⏱ The most practical "2-second/3-second rule" for Hong Kong highways
step:
- Choose a fixed reference point (lamppost, road sign, road marking) that the vehicle ahead of you has passed.
- When the current car passes this point, the timing starts immediately;
- If you reach that point in less than 2 seconds (good weather) or 3 seconds (bad weather/night time), you are too close.
Why does it work?
- Both reaction distance and braking distance are considered;
- It is not affected by your actual vehicle speed because the time interval is automatically adjusted according to the vehicle speed.
📊 Speed and safety distance comparison (based on Hong Kong)
| Speed (km/h) | Recommended distance in good weather (meters) | Bad weather/wet road (m) | It takes about seconds |
|---|---|---|---|
| 70 | 40–45 | 60–65 | 2–3 seconds |
| 80 | 50–55 | 75–80 | 2–3 seconds |
| 100 | 70–75 | 105–110 | 2–3 seconds |
| 110 | 85–90 | 125–130 | 2–3 seconds |
Simple method: Speed number × 0.7 ≈ safe distance (meters) (Sunny day)
🛣 Common variables and responses on Hong Kong's expressways
1. Dense export and diversion
- Example: On West Kowloon Highway near the Western Harbour Crossing exit, vehicles may suddenly cut off from the exits in a short distance.
- Countermeasures: Increase the safety distance in advance and leave space for vehicles entering and exiting.
2. Large vehicles block the view
- Example: Container trucks are densely packed on Tuen Mun Highway, making it difficult to judge the road conditions ahead;
- Countermeasure: Add an extra 1-2 seconds of distance to buffer for unseen changes ahead.
3. Rain/slippery road
- Example: When it rains on Qingsha Highway, the bridge surface is extremely slippery;
- Solution: Upgrade the 2-second rule to 3–4 seconds.
4. Driving at night
- With low visibility, reaction time is naturally slower;
- Strategy: Allow 0.5–1 second more space than usual.
❌ Common Mistakes Hong Kong Drivers Make
- "If you follow closely, you won't be cut off" → Being cut off is normal. A safe distance is a lifeline, not a "position-occupying line".
- Ignore the weather influence → Using the sunny distance when it is raining will more than double the braking distance.
- Underestimating reaction time → You are not a robot. A 0.5 second slow reaction time can mean a difference of several meters.
- Following a large vehicle too closely → You cannot see what is ahead and cannot predict in advance.
💡 Editor's private practice method
- Practice the 2-second method daily : Even if you are not on the highway, you can practice it in the city to develop good habits.
- Try to experience the ABS actuation distance (in a safe and enclosed area): Understand the differences in braking performance of your vehicle model at different speeds and road conditions.
- Observe the distance to the car behind you : If the car behind you is too close, you can lightly turn on the brake lights or gradually increase the distance between you and the car in front to avoid being hit when you stop suddenly.
📍 Common highway safety distance sections in Hong Kong where they are often overlooked
- Tolo Highway near Tai Po Market Toll Plaza : Traffic jams are common after turning, and vehicle speeds vary greatly.
- The front section of the West Kowloon Highway leading to the Western Tunnel : There are many vehicles merging and exits are densely packed, so novice drivers tend to follow too closely.
- The downhill exit of Chengmen Tunnel on Qingsha Highway : the line of sight is short and the braking distance is longer after accelerating downhill.
✅ Summarize the editor's four-word tips
Remember "second, acceleration, preparation, and stability" for safe distance at high speeds:
- Seconds : Measure using the 2-second/3-second method, rather than estimating by eye.
- Plus : In case of rain, at night, or with poor visibility, increase the distance.
- Pre-emptive : Observe exits, slowing vehicles, and road conditions in advance.
- Steady : Maintain a steady speed and avoid frequent sudden braking and acceleration.
