Wedges are quite effective tools for using forces in directions perpendicular to the applied force. In a collision, vertical components, if allowed to be raised, can lift the rear end of trucks and buses, thus aggravating the underride effect and consequences.

• WHENEVER THE UNDERRIDE GUARD IS WEAKER THAN NECESSARY.

• WHENEVER THE UNDERRIDE GUARD IS PLACED HIGHER THAN THE CAR FRONT BUMPER.

• WHENEVER BOTH HAPPEN SIMULTANEOUSLY.

• THE LIGHTER THE TRUCK (SMALL OR UNLOADED), THE WORSE IS THE PROBLEM.




Demonstration of the wedge effect in a real accident occurred in Australia:


NOTE: IN A CRASH TEST PROMOTED BY UNICAMP, GENERAL MOTORS AND MERCEDES BENZ, A SMALL GM CORSA WAS ABLE TO LIFT A PARKED TRUCK WITH A 10 TON LOAD, SOME 15 CM.

During braking, car front bumpers can have their height substantially reduced in relation to the ground, and as a light vehicle's suspension is soft for comfort reasons, this height reduction can be extreme, promoting even more the underride effect.

CONCLUSION: THE WEDGE EFFECT IS EXTREMELY IMPORTANT AND CAN NULLIFY AN APPARENTLY EFFICIENT UNDERRIDE GUARD. THEREFORE, IT CANNOT CONTINUE TO BE NEGLECTED IN ALL RULE MAKING PROCESSES.