Safe Stopping Distance Calculator
Recommended Stopping Distance:
Enter values and click calculate to see your recommended stopping distance.
Key Takeaways
- New Zealand law expects you to leave at least one car length for every 10 km/h you’re travelling.
- Road surface, weather, vehicle weight and your reaction time all shift the ideal gap.
- At 50 km/h aim for roughly 2.5m (8ft); at 80 km/h about 4m (13ft).
- Heavy‑duty brakes, wet roads or night driving require extra space.
- Regularly check your mirrors and give yourself enough time to stop safely.
When you pull up behind another vehicle, the stopping distance behind a car is the space you leave between your front bumper and the rear of the vehicle in front, allowing you to stop safely without a collision becomes the single most important factor for avoiding rear‑end crashes.
What the Road Code Says
The New Zealand Road Code sets out the legal expectations for drivers on public roads, including safe following distances and stopping requirements doesn’t give a fixed number of metres. Instead it uses a rule‑of‑thumb: keep at least one car length for every 10 km/h you’re travelling. This translates to about 2.5m (8ft) at 30 km/h, 5m (16ft) at 60 km/h, and so on.
Why the rule is written this way becomes clear when you look at the science behind stopping distance.
Breaking Down Stopping Distance
Stopping distance is the sum of two components:
- Thinking distance - how far your car travels while you realise you need to stop.
- Braking distance - how far the car rolls after you apply the brakes.
Both parts are influenced by a handful of entities that we’ll explore next.
Speed
Speed is the biggest driver of distance. Kinetic energy rises with the square of speed, so doubling your speed quadruples the braking distance. The speed measured in kilometres per hour (km/h), determines the kinetic energy that must be dissipated when you stop is the primary variable in any calculation.
Road Surface
A dry, clean asphalt offers the most grip. Gravel, sand, or icy patches can double the distance needed to stop. The road surface refers to the material and condition of the pavement, influencing tire traction is therefore a critical factor to adjust for on the fly.
Weather Conditions
Rain, snow, or even strong wind reduces tyre contact and can make braking erratic. The weather conditions include precipitation, temperature, and wind, all of which affect vehicle stability and stopping performance should prompt you to increase the gap by at least 50%.
Vehicle Type and Braking System
Cars equipped with ABS (anti‑lock braking system) stop faster than those without, but heavy‑duty trucks need far more space. The braking system covers components like disc brakes, ABS, and electronic stability control that influence how quickly a vehicle can decelerate and the vehicle means the make, model, and weight of the car you’re driving, each with its own braking characteristics should be factored into your judgement.
Reaction Time
Average reaction time for a sober driver is about 1.5seconds. Distractions, fatigue, or alcohol can stretch this to 2.5seconds or more. The reaction time is the interval between perceiving a hazard and beginning to apply the brakes directly adds to the thinking distance.
Recommended Stopping Distances by Speed
| Speed (km/h) | One‑car‑length rule (metres) | Practical minimum gap* (metres) |
|---|---|---|
| 30 | 2.5 | 3.0 |
| 40 | 3.5 | 4.2 |
| 50 | 5.0 | 6.0 |
| 60 | 6.5 | 7.8 |
| 70 | 8.0 | 9.6 |
| 80 | 9.5 | 11.5 |
*These numbers add a 20% safety margin for real‑world variables such as wet roads or slight driver delay.
Practical Tips for Maintaining a Safe Gap
- Use the “two‑second rule”: pick a fixed point (a sign or tree) and make sure it takes at least two seconds for you to reach that point after the vehicle in front passes it.
- Increase to three or four seconds in rain, fog, or at night.
- When following a larger vehicle (bus or truck), give an extra car length because you can’t see far ahead of them.
- Regularly check tyre pressure; under‑inflated tyres increase braking distance by up to 10%.
- Practice gentle braking to avoid lock‑ups; abrupt stops often force the driver behind you to swerve.
- Keep a safe buffer at traffic lights; the moment the light turns green, the car ahead may accelerate, and you’ll need space to react.
Common Situations and How to Adjust Your Gap
Approaching a Stop Sign
Begin decelerating early, and aim for a gap that lets you stop without a hard brake. On a dry road at 40 km/h, a 3‑metre gap is usually sufficient.
Traffic Lights
If the light is amber and you’re close, you may need to stop. Ensure you have at least the minimum gap for the speed you’re travelling; otherwise you risk a rear‑end if the car ahead accelerates.
School Zones
Speed limits drop to 20 km/h. The required gap shrinks, but children are unpredictable-maintain at least a 2‑second buffer regardless of the rule.
Heavy Vehicles
Follow a truck with an added car length because their brakes take longer and they may stop more abruptly.
What Happens If You’re Too Close?
Being within the legal minimum can lead to a traffic infringement under the Road Code, especially if a rear‑end collision occurs. More importantly, the physics are unforgiving: at 60 km/h, a gap of only 1metre means you’ll need to brake at roughly 0.8g, a force that can cause tyre lock‑up and loss of control.
Quick Checklist Before You Move Off
- Identify your current speed.
- Apply the one‑car‑length‑per‑10km/h rule.
- Adjust for road surface and weather (add 20‑50%).
- Consider vehicle weight and brake type.
- Confirm you have at least two seconds of visual clearance.
Following this routine helps you keep a safe stopping distance behind a car and reduces the chance of an accident.
Frequently Asked Questions
What is the legal definition of a safe following distance in New Zealand?
The Road Code advises keeping at least one car length for every 10 km/h you travel. This guideline is meant to give you enough space to stop safely under normal conditions.
How does wet weather change the required gap?
Wet surfaces can double braking distance. Add roughly 50% to the one‑car‑length rule, or simply switch to a three‑second following rule.
Do larger trucks need a longer gap?
Yes. Because trucks have greater mass and longer stopping distances, you should add at least one extra car length when following them.
Is the two‑second rule enough for city driving?
In most urban settings it works, but reduce speed and increase to three seconds in rain, fog, or when the road is slippery.
What penalties apply if I cause a rear‑end collision?
You may face a traffic infringement, demerit points, and potentially higher insurance premiums. Severe cases can lead to court charges for careless driving.