Forward collision warning systems with adaptive braking and anticipatory collision safety features can mitigate severity in 53 percent of rear-end collisions.

An evaluation of advanced brake assistance systems.

01/01/2013 12:00:00 AM
Nationwide,United States

Summary Information

This paper examined the effectiveness of forward collision assistance systems used to help drivers avoid rear-end collisions and mitigate crash severity. The systems evaluated included one or more of the following: FCW (forward collision warning), EBA (emergency brake assist), and AEB (autonomous emergency braking). AEB included subcategories of CMB (autonomous collision mitigation braking) and CIB (autonomous collision imminent braking).

Findings in this paper were based on: 1) A driving simulator experiment that examined the behavior of real world drivers equipped with forward collision warning and automated brake assist systems. 2) Field tests that looked at equipment performance and changes collision avoidance in the real world; 2) Analyses of Spare Part Calls from an OEM that can estimated changes safety based on changes in spare parts needed for repairs; 3) Analyses of property damage liability, collision, bodily injury liability, personal injury protection and medical payment coverages associated with these technologies.


Driving Simulator Tests
The effectiveness of a driver braking assistance system was assessed using a Berlin dynamic driving simulator. The system was designed to use radar to monitor vehicle headways, warn a driver if the headway was too small, and then optimizes brake force if needed to mitigate or avoid a rear-end collision.

A total of 110 ordinary drivers were recruited to participate and cope with three types of driving situations that often lead to rear-end collisions. Half the drivers drove a vehicle equipped with conventional Brake Assist System (BAS - shortens stopping distance by boosting brakes when maximum braking is applied), and the other half used BAS PLUS (conventional brake assistance plus enhanced braking based on input from forward radar system).

Field Tests
Field testing was performed on vehicles driven by non-expert drivers in Europe, United States, Japan, and South Africa. Data were collected from over 1 million km driven. Activation events were recorded using in-vehicle video and on-board data collection systems in each test car. These vehicles were equipped with both forward collision warning and adaptive brake assist systems.

Analyses of Spare Part Calls
The evaluation was based on changes in the rate of spare parts calls for the S-Class model 221 delivered by Mercedes-Benz in Germany between launch and end of 2008. In this period about 40,000 cars were sold and registered in Germany. About 40 percent of these cars were equipped with forward radar scanning adaptive cruise control and forward collision warning systems, anticipatory seat belt tensioners, adaptive brake and brake assistance, and parking assistance. The remaining 60 percent were equipped with parking assistance only.

Real-World Effectiveness With Insurance Data
Insurance claims data were analyzed for collision avoidance systems offered on Acura, Mercedes-Benz and Volvo passenger vehicles. The following specifications were excerpted from the source report.

"Acura with auto brake" includes a forward collision mitigation system that uses visual and auditory alerts to warn drivers when speeds and distance data indicate crash risk with a leading vehicle. If the driver does not respond by reducing speed, the system will automatically tug at the seat belt to get the driver’s attention and begin braking to mitigate severity , but probably not prevent a crash. This mitigation strategy becomes functional at speeds over 15 km/h and deactivates when speed drops below 15 km/h. It was bundled with an adaptive cruise control system.

"Mercedes-Benz with auto brake" means that the vehicles were equipped with forward radar scanning adaptive cruise control as well as a driver assistance system that have a low end operational speed threshold of 30 km/h.

"Volvo vehicles without auto brake" use adaptive cruise control and forward collision warning radar sensors mounted on bumpers to detect collision risk. Auditory and visual alerts, such as red lights in a heads-up windshield display, are provided to drivers. If the driver brakes the warnings are canceled. The forward collision warning system is active only between speeds of 30 and 180 km/h. Vehicles equipped with forward collision warning also have adaptive cruise control and distance alerts. "Volvo vehicles with auto brake" have a forward collision warning system that includes some autonomous emergency braking.


Driver Simulator Test
Results showed that the combination of forward collision warning (FCW) and BAS PLUS lead to a 75 percent lower accident rate (combined) compared to the conventional BAS. For those subjects who reacted too late to avoid the accident, BAS PLUS produced a mitigating effect: impact speed was reduced by 35 percent on average.

Field Test
No forward collision warning activation without any driver reaction was observed. Hence the audible/visual warning, a combination of warning tone and icon, proved to be very effective. Interestingly 44 percent of all drivers were already braking when a forward collision warning occurred. Of the drivers who responded to forward collision warning by applying the brake:
  • 65 percent acted within 0.4 second after the warning
  • 87 percent acted within 0.8 second after the warning
  • 97 percent acted within 1.0 second after the warning
Data collected specifically from the Mercedes-Benz Collision Prevention Assist (CPA) system that includes a forward collision avoidance, and adaptive braking and brake assist was found to be able to address 71 percent of all rear-end pre-crash situations.

Analyses of Spare Part Calls
The rate of repairs of front-end bumpers was reduced by 5 percent, the repair rate of a front-end bumper in combination with a cross member dropped by 15 percent and repairs involving front-end bumper, cross and longitudinal member assembly dropped by 22 percent. These data show that forward radar scanning adaptive cruise control with the included driver assistance features including anticipatory seat belt tensioners was effective at reducing the number and severity of frontal crashes.

Real-World Effectiveness With Insurance Data
Accident research shows that drivers do not always react as quickly as is necessary in critical moments. Using driver assistance packages that support FCW and advanced braking systems 53 percent of all rear-end collision could be mitigated in their severity and 35 percent could be avoided. The risk for an occupant of the striking car of being seriously injured is reduced by at least 35 percent. Claim frequency reduced by 14.3 percent in the insurance coverage property damage liability.

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Advanced Brake Assist – Real World effectiveness of current implementations and next generation enlargements by Mercedes-Benz

Author: Schittenhelm, Helmut

Published By: 23rd International Technical Conference on the Enhanced Safety of Vehicles (ESV)

Prepared by the National Highway Traffic Safety Administration (NHTSA)

Source Date: 01/01/2013 12:00:00 AM



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Benefit ID: 2015-01055