Safe Following Distance for Trucks

“The Space Between” is the first instalment in a six-part road-safety series proudly developed by roadtrains.com.au in partnership with Scania Australia.

Cold, damp air hung lazily over the Windmills Rest Area near Breadalbane, south-west of Goulburn, in the pre-dawn darkness on Tuesday, June 30, 2026.

Beyond the reach of the parking-bay lights, the surrounding paddocks and hills remained hidden beneath the blackness of a midwinter morning as frost settled across the ground. Inside the rest area, truck engines ticked as they cooled, curtains were drawn across sleeper-cab windows, and drivers slept in their cabs, intending to wait for daylight before continuing their journeys north along the Hume Highway.

Out on the highway, another stream of headlights pushed steadily through the darkness.

Then, around 5am, the morning exploded.

A truck entering the northbound rest area was struck from behind. The force of the impact shunted it into four semi-trailers parked inside the bays. Within moments, six trucks were burning. Loads containing butane cans, resin, memory foam and alcohol fed an inferno that sent flames and explosions tearing through the darkness.

Emergency crews established a 300-metre exclusion zone as more than 70 firefighters and specialist personnel fought to bring the scene under control.

Somehow, all six drivers escaped without serious injury.

Police described it as nothing short of a miracle. But miracles are not a road-safety strategy.

The investigation will determine the full circumstances surrounding the Breadalbane crash. What the wreckage already demonstrates, however, is the devastating amount of energy released when a heavy vehicle collides with the vehicle ahead, with nowhere left to go.

Six trucks were destroyed, a major national freight route was closed, and an ordinary winter morning became one of the most confronting heavy-vehicle crash scenes experienced by attending police.

It all began when the space between one truck and the next disappeared.

That space is not wasted road.

It is reaction time. It is braking distance. It is visibility. It is the room required to recognise a developing hazard, decide what to do and bring a loaded combination safely under control. Once that space has disappeared, even the most experienced driver may have very few options left.

That is why roadtrains.com.au, in conjunction with Scania Australia, has developed this six-part road-safety series. Both organisations share a genuine commitment to improving safety through better information, better driving decisions and a clearer understanding of the technology now working alongside professional drivers.

In this first instalment, The Space Between, we examine following distance, reaction time, heavy-vehicle stopping distances and the growing influence of collision-avoidance technology.

Because sometimes the most important safety equipment on a truck is the empty piece of road directly in front of it.

 

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The Space Between

Understanding Truck Stopping and Following Distance

Before we talk about following distance, we need to understand stopping distance, because that is where safe spacing really begins. Every vehicle requires space to stop. The faster it is travelling, the heavier it is and the poorer the conditions, the more road it will require. For a heavy vehicle, that distance can be substantial. Once the space ahead has been used up, no amount of experience, technology or wishful thinking can put it back. Following distance is simply the driver’s way of protecting that stopping distance before it is needed.

How much road does a vehicle need to stop?

Stopping distance is not simply braking distance. It is reaction distance plus braking distance. Reaction distance is the ground covered while the driver identifies the hazard, recognises the problem, decides what to do, moves their foot to the brake and begins applying pressure. Braking distance is the ground covered after the brakes begin doing their work. Put the two together, and you arrive at the real-world space required to avoid running into whatever is happening ahead.

The accompanying stopping-distance figures should be treated as indicative rather than fixed test results, because actual stopping distances vary considerably depending on load, tyres, brake condition, road surface, gradient, weather, suspension, brake balance, driver reaction, vehicle age and the technology fitted to the vehicle. The important point is not whether a particular combination stops in 149 metres, 160 metres or 185 metres under a specific set of test conditions. The important point is that the numbers are large enough to change the way we drive.

At 100 km/h, a passenger car may require around 100 metres to stop in good, dry conditions, while a heavy combination may require significantly more. A dual-cab ute towing a caravan, horse float or boat may also need considerably more room than its driver expects, particularly if the trailer is heavily loaded, the brake controller is poorly adjusted, the tyres are ageing, or the driver has failed to allow for sway, downhill gradients or a wet road.

For the professional driver, the lesson is simple: build the space before you need it, because once the problem has started, it is too late to go looking for it.

The road disappears faster than most people think.

Most drivers think of speed in kilometres per hour, which makes sense when calculating how long it will take to travel from one town to another. But when it comes to stopping distance, the crucial figure is metres per second. That is the number that counts when a brake light comes on, a car darts into the safety gap you have deliberately created, or traffic suddenly bunches up over a crest.

At 100 km/h, a vehicle covers almost 28 metres per second. That is more than the length of a B-double in the time it takes to say, “What’s he doing?” At 80 km/h, the vehicle is still covering more than 22 metres every second, and even at 60 km/h, it is moving at nearly 17 metres every second.

Once speed is viewed this way, following distance stops being a vague road-safety message and becomes a very practical calculation. At 60 km/h, a four-second gap is approximately 67 metres. At 80 km/h, it is approximately 89 metres; at 100 km/h, it is approximately 111 metres. That may sound like a lot of empty road, right up until the vehicle ahead stops suddenly.

Reaction distance: the road you use before braking

Even an alert driver needs time to react. The driver must see the hazard, understand what is happening, make a decision and physically apply the brake. If the driver is distracted, fatigued, checking mirrors, reading the traffic ahead, watching a side road, searching for a street sign, dealing with glare or monitoring a vehicle behaving unpredictably, that reaction time can increase rapidly.

Using a practical reaction time of approximately 1.5 seconds, a vehicle will travel 25 metres at 60 km/h, 33 metres at 80 km/h and 42 metres at 100 km/h before meaningful braking has even begun.

At highway speed, more than 40 metres can disappear while the driver is still processing what is happening ahead. That is why tailgating is such a poor strategy. It removes the one part of the crash the driver can control before the trouble starts: time. For a heavy-vehicle driver, that time is everything.

When the car brakes before the driver does

But today, there is another important factor to consider: the vehicle ahead may not always be braking because its driver has made a conscious decision to do so. Many modern cars are fitted with Forward Collision Mitigation, Autonomous Emergency Braking or a similarly named collision-avoidance system. The terminology varies between manufacturers, but the basic principle is much the same: cameras, radar or a combination of sensors monitor the road ahead.

If the system detects a developing collision risk and the driver has not responded quickly enough, it can warn the driver and, in some situations, automatically apply the brakes. In a genuine emergency, that technology can be extremely effective because AEB can begin braking before an inattentive or slow-reacting driver has completed the normal perception-and-reaction process.

As we have already seen, a vehicle can cover more than 40 metres at 100 km/h during a 1.5-second human reaction period. If the vehicle’s safety system intervenes before the driver reacts, part of that reaction distance may be removed from the stopping event. From the truck driver’s seat, the car ahead may therefore appear to stop with surprising urgency because the first part of the braking response has been initiated by the vehicle’s safety system rather than the driver’s right foot.

That is the upside. The caution is that these systems are not infallible. In a complicated traffic situation, a collision-avoidance system may occasionally misread what is happening ahead. A vehicle turning out of the lane, roadside infrastructure, unusual road geometry, poor visibility, heavy rain, glare or traffic moving in an adjacent lane may trigger a warning or, in some cases, a braking response.

Inside the car, the driver may hear a sudden alarm, feel a sharp brake pulse or find the vehicle braking automatically. But the truck driver behind does not receive an explanation. All they see is the car ahead suddenly shedding speed, often with little warning and for no obvious reason.

That is the critical point for a professional heavy-vehicle driver. The car may brake hard the instant its brake lights appear. It may slow sharply for a hazard the truck driver cannot yet see, or for something the car’s sensors believe they have detected. Whether the system has identified a genuine danger or simply misread the situation makes no difference to the truck driver. The heavy vehicle still has to stop. And stop before it collides with the rear of the car in front.

This is another reason the four-second crash avoidance space is so important. The gap is not only there for the driver who brakes late. It is also there for the car that brakes early, the distracted driver, the nervous driver, the overloaded ute, the caravan that begins to move around and the modern vehicle whose collision-avoidance system suddenly decides it has seen trouble.

Braking distance: where speed, tyres and road surface join the conversation

Modern heavy vehicles can stop remarkably well compared with the trucks of old. ABS, EBS, improved braking systems, better suspension, better tyres and increasingly sophisticated stability systems have all helped, but physics has not retired.

The amount of energy a vehicle must shed increases sharply with speed. In plain English, a relatively small increase in speed can produce a much larger increase in braking distance. A vehicle travelling at 100 km/h is not simply a little harder to stop than one travelling at 60 km/h. It carries considerably more kinetic energy, and that energy must be converted into heat through the brakes, tyres, and road surface.

Then there is mass. A well-maintained heavy vehicle can stop very effectively, but it still requires room.

The driver does not get to cheat physics simply because someone in a hatchback wants the truck’s stopping gap.

The four-second crash avoidance space

For a heavy-vehicle driver, four seconds should be regarded as the starting point, not the luxury setting and certainly not the soft option.

There are, however, two different rules being discussed here, and they should not be confused.

The road rules require every driver to remain far enough behind the vehicle in front to stop safely and avoid a collision. There is also a separate minimum-distance rule for long vehicles. A vehicle measuring 7.5 metres or longer must generally remain at least 60 metres behind another long vehicle. For a road train, that minimum increases to 200 metres. The rule does not apply on a multi-lane road, on a road within a built-up area or while the driver is overtaking.

It is worth correcting a common misunderstanding here. The 200-metre requirement applies to road trains. It is not simply triggered because the vehicle happens to be operating in a road-train area.

Those fixed distances are legal minimums intended to maintain separation between long vehicles. They are not a guarantee that the driver has enough room to stop safely in every situation. The broader road rule still requires the driver to leave sufficient distance to stop without colliding with the vehicle ahead.

As we mentioned earlier, at 100 km/h, a truck travels almost 28 metres every second. That means a 60-metre gap represents only a little over two seconds. A four-second crash avoidance space is approximately 111 metres.

That distinction matters.

Official road-safety guidance in Queensland, Tasmania and most other states recommends that a heavy vehicle allow at least four seconds behind the vehicle in front. In wet weather, it recommends increasing that to at least eight seconds.

A professional driver is not merely watching the speedometer to ensure their truck’s speed limiter is set at 100 km/h, not 98 km/h, and hoping the brakes will sort everything out. They are managing mass, combination length, tyre grip, brake condition, traffic flow, visibility, road surface, gradient, load behaviour and the unpredictable actions of everyone around them.

A four-second gap gives the driver time to see the problem, understand what is happening and begin doing something useful about it. It also gives the braking system time to respond and the combination time to settle before the full braking effort arrives.

Most importantly, it provides some working room when another road user makes a poor decision.

At highway speed, four seconds is not a small distance. It is the space that allows a professional driver to turn someone else’s mistake into a controlled braking event rather than a rear-end collision.

How to work out the four-second gap

Choose a fixed point beside the road, such as a sign, guidepost, tree or bridge rail. When the rear of the vehicle ahead passes it, count steadily: “One thousand and one. One thousand and two. One thousand and three. One thousand and four.”

Your truck should not reach the same point until the count is finished. If it does, you are too close.

Using time rather than distance means the gap automatically increases with speed.

And keep looking beyond the vehicle directly in front of you. The earlier you spot trouble developing, the less braking you will need.

Takeaways for professional drivers

Following distance remains one of the few things a professional driver can control in a world filled with unpredictable motorists, nervous caravan drivers and modern cars that may brake before their drivers do. The basic principle is to leave the gap anyway, and when somebody fills it, rebuild it.

When the traffic becomes messy, ease off slightly and create more room. When you are being tailgated, increase the space ahead so you are not forced into harsh braking that the driver behind may be unable to match.

When following a modern car, allow for the possibility that its collision-avoidance system may brake sooner or more aggressively than its driver would have. When following a caravan, leave room for changing speeds, late braking, sway and an inconsistent line through corners. When following another heavy vehicle, think beyond the legal minimum and ask whether you can see enough, stop safely enough and retain an escape path if the road ahead suddenly changes.

When another road user steals your gap, do not take it personally. Rebuild the space. The gap is not there to win an argument; it is there to keep the truck, the load and everyone around it out of trouble.

The best heavy-vehicle drivers are smooth because they are looking a long way ahead. They do not rely on last-second braking because they have already seen the problem developing. That is not old-fashioned driving. That is professional driving.