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Flashing Brake Lights

BMW Brake Force Display (BFD) - Are they legal?

You may have noticed that certain cars brake lights will flash when the car is braking heavily. It’s a technology first introduced by BMW aimed to highlight to other drivers that a car is braking heavily, referred to as Brake Force Distribution, or BFD, it comes in various forms and is implemented differently in different markets. Whilst BFD is generally considered a step forward in safety and can actually be coded into a cars ECU (engine control unit), even if not installed as standard by the manufacturer. However it can take on various forms and it’s useful to know if flashing brake lights are legal. For example, what might be legal on a car designed and built for the EU and UK market, may not be legal for use in the USA.

What different types of BFD are there?

Flashing Brake Lights
Installed on EU market cars, the brake lights will flash under certain criteria. As the system is designed to warn other drivers, particularly those following of heavy brake application, the flashing brake lights aim to draw extra attention to the fact that the car in front is braking heavily in an attempt to stop as quickly as possible. Rather than merely to reduce speed a little, the flashing brake light BFD aim to warn other drivers of an emergency braking situation so that they can react accordingly. Under certain criteria, the brake lights will flash

Extra Bright Brake Lights
There are different types of BFD that are installed on different models, usually depending on their market. In the US (and other markets that share US specifications), the brake lights themselves are split into different sections. Under normal braking, only the main section of the brake light illuminates, however under heavy braking the full extent of the brake light illuminates including the fog light section of the rear cluster. This extra section is fitter with higher output bulbs to further increase the intensity of the brake light, further enforcing to others that the car is breaking in an emergency.

Are Flashing Brake Lights Legal in the UK?

Yes – There is no specific law within the UK’s own vehicle lighting regulations that suggests otherwise. Likewise, the widely adopted EU regulation ‘Uniform provisions concerning the approval of vehicles with regard to the installation of lighting and light-signalling devices’ sets out the requirements for emergency stop lighting, defining it as;

Emergency stop signal’ means a signal to indicate to other road users to the rear of the vehicle that a high retardation force has been applied to the vehicle relative to the prevailing road conditions.
Whilst options, where installed they must adhere to the following regulations

The emergency stop signal shall be given by the simultaneous operation of all the stop or direction-indicator lamps fitted as described as below;
  • All the lamps of the emergency stop signal shall flash in phase at a frequency of 4.0 ± 1.0 Hz.
  • However, if any of the lamps of the emergency stop signal to the rear of the vehicle use filament light sources the frequency shall be 4.0 +0.0/-1.0 Hz.
  • The emergency stop signal shall operate independently of other lamps.
  • The emergency stop signal shall be activated and deactivated automatically.
  • The emergency stop signal shall be activated only when the vehicle speed is above 50 km/h and the braking system is providing the emergency braking logic signal defined in Regulations Nos. 13 and 13-H.
  • The emergency stop signal shall be automatically deactivated if the emergency braking logic signal as defined in Regulations Nos. 13 and 13-H is no longer provided or if the hazard warning signal is activated.

Are Flashing Brake Lights Legal in the USA?

Interestingly, the US Department of Transport regulations do not permit flashing brake lights to warn of a vehicles heavy braking / emergency stop warning. Rather they permit an increased intensity of brake lights to provide other drivers with warning that the vehicle is braking heavily.

Flashing Hazard Lights under Braking?

A similar feature and much more widely used technology is the use of flashing hazard warning lights under heavy braking. The main difference between BFD and hazard lights flashing under braking is that it is not only under heavy braking where a cars hazards warning lights might flash automatically. You’ll likely notice the hazard warning lights of a car flash if the ABS has been triggered or in some cases if the traction control system has been activated.

Driving in snow and ice, particularly when you are not used to it, is likely to keep a cars ABS (anti-lock braking system) busy as the system automatically releases and reapplies a cars brakes to ensure maximum traction and minimum braking distance. However, it’s not always the case that heaving braking will trigger the system, although in normal driving conditions that is the likely cause.

Can you code BFD yourself?

Yes you can, however  you should check with local restrictions and laws to ensure your car is in compliance with regulatory specifications. Whilst many in the US consider the flashing brake light system is preferable, it is not legal to use this system and is why BMW use the extra intensity brake light system.
BMW Brake Force Distribution - Flashing Brake Lights v High Intensity Brake Lights

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