Safety & Security

Intelligent brake light: A proposal

In today's dense traffic, traditional brake lights in many situations no longer serve the purpose to warn the trailing vehicle of a slow-down – because they are on anyway during a slope, or because the traffic is so dense that the following vehicle is too close anyway. The article at hand proposes an intelligent brake light system that could do away with these shortcomings.

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i-b.l. is a safety technology that integrates with existing adaptive cruise control (ACC) and operates in tandem with conventional brake lights. ACC with i-b.l. eliminates the slow human reaction time of the host driver from the timing sequence that begins with the detection of a downstream traffic stoppage and ends with notification to the trailing driver of the pending need to brake. ACC with i-b.l. operates at all times, at all speed ranges, in both highway and city driving. ACC with i-b.l. provides the greatest possible protection from rear-end collisions. 

  i-b.l. consists of two main components: a front mounted radar like that already incorporated into many vehicles for their ACC, and a rear-mounted light integrated with the vehicle's existing brake light system such as the upper middle brake light (UMBL) as shown below. (For other i-b.l. design options, including early activation of existing brake light elements, see the discussion later in this paper).

In a combined ACC/ i-b.l. system, the ACC radar remains operating at all times the vehicle is in motion – even if the braking and accelerating features are de-activated or put on standby. ACC radar monitors the speed of the forward vehicle, and upon detection of any significant deceleration, automatically activates the i-b.l. light to alert the trailing driver of the pending slowdown. i-b.l. operates intuitively much like conventional brake lights, but informs the trailing driver of the braking status two cars in front of them instead of just one.

The system operates independently of the host driver's actions. Thus, if the host driver is distracted, the trailing driver will still be alerted to the slowdown and can begin to brake. And because the ACC/ i-b.l. system removes the host driver and their slow reactions from the operating loop, the signal is communicated to the trailing driver almost instantaneously – providing an extra .7 – 1.2 seconds of braking. At freeway speeds, that provides an extra 100 feet of braking distance. 

In today's dense traffic, most of the braking you do is a result of slowdowns or stoppages due to the traffic ahead of you. Thus, most braking events involve three vehicles: your vehicle, a forward vehicle, and a trailing vehicle. It is relevant, then, to re-ask the question: when driving in today's dense traffic and the forward traffic starts to slow, what is the best technology to prevent a trailing tailgating driver from rear-ending your vehicle when you begin to brake? Your brake lights are still good, and they will help. But the real goal now is to convey to that trailing driver that the car in front of you is slowing - and thus you both need to begin braking. The further goal is to convey that information to them as quickly as possible so braking can begin at the earliest possible moment.

With conventional brake lights, that trailing driver cannot learn of the forward slow-down until you react and apply your brakes. A typical reaction time is 0.7-1.2 seconds during which time both your vehicle and the one trailing you may have traveled 100 feet or more.

 i-b.l. taps into modern technology to offer a better solution. The first step is to take the driver, out of the signaling loop and cut out its slow reaction time. Second, let the ACC radar monitor the speed of the forward vehicle. Then, when a deceleration of that forward vehicle is observed, let that radar device automatically signal the trailing driver by activating a supplemental brake light mounted together with your upper middle brake light.

Operating independently of the driver, the trailing vehicle's driver will learn of the need to stop instantly. That trailing driver gains the 1-3 seconds of extra braking time saved by taking you out of the signaling process. If the forward stoppage is such that only a speed reduction is required, then signaling that driver early, keeps their attention on the road and making it less likely that they’ll allow themselves to be distracted until they see the lights turn off and the flow return to speed.

 ACC vs. i-b.l. or ACC with i-b.l.?

It has sometimes been argued that emerging ACC systems with Stop & Go might take away the time advantages i-b.l. offers in the braking sequence. As the argument is stated: with the advancement of ACC, the forward radar will always be operational and, thus, with the detection of any significant deceleration of the forward vehicle, the ACC system will initiate braking which instantly activates the host vehicle's brake lights and, of course, warns the trailing driver of the pending need to slow down. Doesn’t that make i-b.l. redundant?

The Dutch Ministry of Transport funded an extensive field study - presented at the 2008 IEEE Intelligent Vehicle Symposium - that analyzed driver behavior when they were using vehicles equipped with ACC. It is particularly relevant to this argument. (see references 1 & 2). They make two important observations and deductions from their extensive field study:

1) A majority of drivers transition out of ACC as soon as the traffic density reaches 20-40 vehicles/km/lane; (see article 2.)

 2) Over 40% of drivers transitioned out of ACC due to their desire to accelerate and close the gap in front of them. 72% of those reduced their time-headway (THW) to less than 1 second - meaning they were entering an aggressive drive mode by choice. Significantly, they were reducing their THW into a range deemed 'unsafe' and into a range where no auto manufacturer will allow their system to operate in and still assume responsibility for the increased likelihood of collisions.

 This limit to the utilization of ACC is perhaps stated best in their conclusions:

 "ACC systems should be seen exclusively as safety-comfort-enhancing, [for] as traffic conditions approach the road capacity, drivers will likely inactivate the system and rely on their own driving capabilities."

 As this study clearly shows, when traffic density gets heavy - at the times when advance warnings are needed the most - drivers transition out of their ACC. No auto braking initiated means no brake will be applied and no brake light will be activated, which means no advance warning will be given to the trailing driver. The host driver is put back in the loop adding their 0.7 -1.2 seconds of reaction time into the delay before warning is given.

That is 100 feet of extra travel distance that could be used for braking if that trailing driver is just given the information that the ACC radar can provide. With the proposed hybrid ACC/i-b.l. system, the ACC radar stays active and can provide that valuable information to the trailing driver at all times regardless of traffic density, traffic conditions, or driver mood. The ACC braking and accelerating control is simply put into a 'hold' mode allowing the host driver full control of (and responsibility for) his or her vehicle for aggressive driving but makes the radar data available to i-b.l. for conveyance to the trailing driver.

Further, once a driver of a vehicle equipped with ACC Stop & Go applies their brakes, no further information about the forward traffic can be conveyed since the light is on. For example, as vehicles travel along a freeway with a long downgrade, if the driver needs to apply their brakes just to remain under the speed limit, that will mask any possibility of conveying new braking emergencies. If the host vehicle is a truck or large SUV, the trailing driver will be blind to the road ahead. However, if the host vehicle is equipped with ACC that includes the i-b.l. advance warning light, then downstream emergencies can still be conveyed to trailing drivers. A hybrid ACC/i-b.l. systems gives drivers the convenience of ACC yet offers maximum protection from rear-end collisions.

Design options: a work in progress.

The light form for i-b.l. that best captures the attention of the trailing driver is still being studied. TASI is planning simulations based on several design options – including the radar-activation of standard light elements. But it is our belief that introducing a simple triangular element into the center of the Upper-Middle-Brake-Light (UMBL) will be the easiest design to implement for the following reasons:

1. Such an element is easily definable and can be standardized.

2. The light is positioned where it is most visible – together with the UMBL

3. Working in tandem with standard brake lights, it gives an intuitive understanding of its operation. 

4. It has less impact on the design of the vehicle’s other lights - in most cases this element can be added without significant revisions.

5. As a new element added to the vehicle - rather than a revision to the functioning of existing elements – NHTSA might be more quickly accepting of such a change. (Similar to how the UMBL was approved as a required added element after its safety value was demonstrated.)

Other design options include:

1. Adding a ring-shaped light element concentric to the standard brake light:

2. Adding a light element that is of contrasting color:

Each of the above designs has considerations when approaching NHTSA - for vehicle taillights and their operation fall under their jurisdiction.

Emergency flash mode

i-b.l. allows for a flashing option that can be activated when very high deceleration rates in the forward vehicle are detected. Such an easily added feature better captures the trailing driver's attention and alerts them of the need to take immediate action and hopefully avoid slamming into the host vehicle.

Time-motion study

The attached diagrams in the Appendix illustrate the time advantages that an i-b.l. equipped vehicle can offer for three frequently collision scenarios.

1.      Rear-end collision due to downstream stoppage – highway.

2.      Rear-end collision due to lane change at moment of downstream stoppage.

3.      Rear-end collision due to accordion stop point.

Concluding remarks

 Existing ACC radar already collects data about the speed of forward vehicles. But until drivers are willing to accept DAS control and until such time when full speed Stop & Go can be shown to work flawlessly – both on the highways and around town – that valuable speed data ACC collects will be underused. So, why not use that data? Why not inform that trailing driver of pending stoppages? Why not give them that extra time to brake? The hybrid ACC/i-b.l. brake light system proposes to do just that.

Steve Thorne is head of Research & Development at i-b.l. Engineering, a technology company located in California.   He was educated at the University of California in Berkeley.  He can be reached via email at:  thorne@intelligentbrakelight.com .

References:

Description of the study by the Dutch Ministry of Transport can be found in the two articles:

1.         Francesco Viti, Serge P. Hoogendoorn, Tom P. Alkim, Gerben Bootsma, Driving behavior interaction with ACC: results from a Field Operational Test in the Netherlands.

2.         Jasper Pauwelussen, Michiel Minderhoud, The effects of deactivation and (re) activation of ACC on driver behavior analyzed in real traffic.

2008 IEEE Intelligent Vehicles Symposium, Eindhoven University of Technology Eindhoven, The Netherlands, June 4-6, 2008.

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