Automatic Emergency Braking in EVs and the Speeds It Covers

A reader emailed me after a near miss on a wet ring road. Traffic ahead stopped suddenly, he was doing about 70 mph in a two year old electric crossover, and he assumed the car would brake for him. It flashed a red warning, gave a short sharp pulse of braking, and left the rest to his right foot. He stopped with about a car length to spare and asked me, quite reasonably, whether his automatic emergency braking was broken.

It was not. Automatic emergency braking in EVs is designed around specific speeds, specific targets and specific conditions, and most owners never read where those limits sit. The system in your car is very good at the job it was built for, which is usually the low and medium speed rear end crash. Here is what it covers, where it backs off, and how the extra weight of an electric car changes the picture.

What Automatic Emergency Braking in EVs Actually Does

AEB uses a forward radar, a windscreen camera, or both, to measure the distance and closing speed to whatever is ahead. Most systems work in stages:

Forward collision warning. A chime and a red symbol, usually around 2 to 3 seconds before a predicted impact.
Brake prefill. The system builds hydraulic pressure so your pedal press bites harder and faster.
Partial braking. A pulse or moderate braking to get your attention and shed speed.
Full automatic braking. Maximum braking if you still have not reacted and a crash looks unavoidable.

In an EV, this happens through the friction brakes, not regenerative braking. Regen alone cannot deliver the deceleration an emergency stop needs, so the car calls on the pads and discs just like a petrol car would.

The Speeds It Is Built and Tested For

Speed is where expectations and engineering drift apart the most. Many current systems are tuned to fully avoid a crash only up to roughly 30 to 40 mph, and to reduce impact speed above that. Owner's manuals usually state the working range, and it often differs between vehicles, pedestrians and cyclists.

Situation	What many current systems do	US rule for new cars from September 2029
Stopped car ahead, city speeds	Often avoids the crash fully	Must avoid contact up to 62 mph
Stopped car ahead, motorway speeds	Usually warns and reduces speed	Must brake automatically up to 90 mph
Pedestrian crossing in daylight	Varies widely by model	Must work up to 45 mph
Pedestrian at night	Often weaker than daytime	Must also work in darkness

The US standard, known as FMVSS 127, was finalised in 2024 and is far tougher than the voluntary commitment carmakers made for 2022. Some manufacturers have argued the timeline is too short, so the details could still shift, but the direction is clear: today's cars generally do less than the cars of 2029 will be required to do.

Why a Heavy EV Changes the Braking Maths

A mid size electric SUV can weigh 2,300 kilograms or more, often 400 to 600 kilograms heavier than a similar petrol model. Brakes and tyres can handle it, but physics still applies. More mass means more energy to shed, and in the wet that can add metres to a stop. Braking energy rises with the square of speed, so going from 50 to 70 mph nearly doubles the energy the brakes must absorb, whatever the car weighs.

Two habits that matter more in an EV than people think:

Tyre condition. AEB can only brake as hard as the tyres can grip. EV tyres wear faster under instant torque, and a set at 3 millimetres stops noticeably worse in rain than a new set.
Following distance. Use at least a three second gap, more in rain. The system calculates from the gap you give it.

Where AEB Hesitates or Gives Up

Every system has blind spots in what it recognises. These are the situations owners most often report in my inbox:

A stationary vehicle partly in your lane at motorway speed, such as a broken down van on the hard shoulder edge.
Motorbikes, which present a small radar target.
Turning across oncoming traffic at a junction, which older systems were never designed to handle.
Low sun straight into the camera, heavy rain, snow or road salt covering the radar badge.
Reversing, which needs a separate rear AEB system that many cars still lack.

The opposite problem exists too. If your car brakes for shadows or overhead signs, that is a false activation, and I covered it in detail in phantom braking in EVs and how to handle it.

Why Turning AEB Off Is the Wrong Fix

Some owners switch AEB sensitivity to its lowest setting, or turn it off, after one false alarm. Forum advice often encourages this. I disagree. Research by the Insurance Institute for Highway Safety found that forward collision warning with AEB cut police reported rear end crashes by around half. One awkward braking pulse is a small price against that.

A better approach is to set sensitivity to the middle or early warning setting, which gives you the alert sooner without making the car brake more often. Most systems turn themselves back on at every restart anyway, which is deliberate.

How AEB Works Alongside Adaptive Cruise

People often assume adaptive cruise control and AEB are the same system. They share sensors, but they do different jobs. Adaptive cruise uses gentle braking, typically limited to around 0.3 to 0.4 g, to keep a gap. AEB is the emergency layer on top, able to brake far harder. If cruise cannot slow you enough, it hands over with a warning, and AEB steps in only when a crash is imminent. Understanding what adaptive cruise control actually does on the highway makes this handover far less surprising.

Frequently Asked Questions

How do I know the speed range of my car's AEB?

Check the driver assistance section of the owner's manual, which usually lists the working speeds for vehicles and pedestrians separately. Euro NCAP and IIHS test results for your model also show how it performed at specific speeds.

Does AEB work when one pedal driving is on?

Yes. One pedal mode only changes how strongly the car regenerates when you lift off. AEB still applies the friction brakes when it detects an imminent crash.

Should AEB be checked after a windscreen replacement?

Yes. The forward camera usually needs recalibration after a new windscreen or front end repair. Ask the fitter to confirm calibration was done, because a camera aimed a degree off can misjudge distance.

Treat AEB as the Last Line, Not the Plan

Find your car's AEB speed range in the manual tonight, keep it switched on at a middle sensitivity, and give yourself a three second gap with tyres above 4 millimetres. Do that and the system becomes what it was built to be: a backstop for the moment you miss something, not a reason to look away from the road.