What does

What does "redirective" mean?

Posted: 14/01/2015

The attribute "redirective" linked to a road restraint system, whether it is a crash cushion or an end terminal, refers to the way such device redirect the impacting vehicle on the carriageway, in order to avoid:

  • the possibility that such vehicle gets out from the road, which can eventually involve the fall in a slope or the impact against a wall;
  • the possibility that such vehicle becomes an obstacle on the carriageway which should result dangerous for the other vehicles.

The "redirectivity" of a road restraint system is evaluated by a set of crash tests by mean of a vehicle that impacts the side of the device in both the directions of travel. If the device works adequately, the crash is absorbed without any injury for the vehicle occupants and the vehicle is redirected onthe road without any obstruction.

Some road restraint systems - in particular: crash cushions - are available both redirective and non redirective.   

A redirective device has been designed in order to absorb the side impact and to avoid that the vehicle gets out from the road by the redirection.

For this reason, it should be installed to protect fixed obstacles in front of road and highway cusps, enctrances, and exits. Moreover, it results mandatory for the protection of obstacles near working zonesand at bypasses of tunnels.

Unlike a redirective system, a non redirective device has an unknown behavior in case of lateral impact , therefore the safety of the vehicle occupants is not guaranteed. 

On the SMA Youtube channel - https://www.youtube.com/user/attenuatoriurtoSMA - you can watch different crash tests of lateral impact.

Here you can find  the SMA 110P lateral crash test as example as example of this tests: https://www.youtube.com/watch?v=8HQS62nl-T0

The code TC 4.3.110 (in the video) indicates the type of crash test which is performed according to the normative EN 1317-3 (For infromation, pleas consult the European Normative EN 1317 document).

In summary:  

TC = indicates that it is atest on crash cushions;

4 = indicates the vehicle approach. In this case is 15°angled impact;

3 = indicates the mass of the vehicle. In this case, number 3 refers to a vehicle with a mass of 1500 Kg;

110 = indicates the vehicle speed at the time of impact in Km/h (110 Kmh = 68.351 mph).