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Current emergency braking systems are highly effective

Jun 2018

Vehicle Technology

To help distribute such systems as quickly as possible, the European Commission stipulated the multi-stage introduction of automated emergency braking systems for goods transport vehicles with a maximum authorized mass of over 3.5 metric tons and buses with more than ten seats. Even though some exceptions are necessary depending on usage (e.g. for off-road vehicles), the regulation fundamentally applies to all of these vehicles. Vehicles with a maximum authorized mass of over eight metric tons first registered in the EU from November 2015 must be equipped with an automatic emergency braking assistance system. The second stage comes into force November 1, 2018. The measure will then be extended to cover vehicles weighing over 3.5 tons. At this point, the requirements regarding the systems will increase again for all of the vehicles concerned. They will include a driver warning function, reduce the speed from 80 km/h to 60 km/h if the respective vehicle approaches a stationary obstacle and ensure that the vehicle completely avoids a collision if the vehicle approaches a vehicle driving at 15 km/h.

Systems supplied by most manufacturers already far exceed these requirements (Figure 30). This is also one of the findings determined in a test conducted by the “Allgemeiner Deutscher Automobil- Club” (General German Automobile Club) on three current emergency truck braking assist systems. Everyday driving situations were investigated to determine the effectiveness and plausibility of the warning behavior of the safety systems and how frequently warnings occurred. The test result showed that warnings occur only when it is absolutely necessary and a situation risks becoming unsafe. The test also showed that the automatic emergency braking system (AEBS) is not noticeable during normal journeys, only adaptive cruise control (ACC).

Comparing old and new braking systems

A test conducted by DEKRA Accident Research and Crash Test Center compared the braking performance of a modern articulated truck with that of an articulated truck from the 1990s. Both vehicle combinations were loaded to an overall mass of 38.5 tons. The objective of the tests was to demonstrate the differences in the braking distance from a speed of 80 km/h in identical environmental conditions. Vehicles that are on the road in this form were chosen. The fact that the vehicles had different tires, thereby resulting in slight inaccuracies, is a given but does not alter the core of the results.

The tests showed that the average deceleration of the modern articulated truck from the moment the accelerator was released and full braking was initiated was around 6 m/ s2. The braking distance at 80 km/h was approximately 41 meters. In the case of an articulated truck from 1997, the average deceleration was 4.3 m/s2. At 57 meters, the resulting braking distance was 16 meters longer. The residual speed of the older articulated truck was 43 km/h at the point at which the new articulated truck came to a stop (Figure 1–3).

Comparing the braking distance of a modern car with that of a modern articulated truck is also interesting – in a direct comparative test, the car’s braking distance was only slightly shorter (Figure 4). The reaction time of attentive drivers is around one second. In this time, a car moving at a speed of 80 km/h travels over 22 meters. It is therefore essential to maintain an adequate safety distance behind trucks (guideline: half the km/h value in meters).

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