The phrase "deceleration forces" refers to the forces that slow down or decrease the speed of an object. These forces act in the opposite direction to the object's motion, causing it to slow down or come to a stop. Full definition
The test complements the offset deformable test as a balance must be found between a restraint system that is stiff enough to restrain a male dummy in the 64km / h test and one that is compliant enough not to put injuriously high deceleration forces on a small female. (euroncap.com)
But this means higher deceleration forces on the driver and passengers and much greater demands on seatbelts. (theaa.com)
When facing forward the acceleration / deceleration forces in a car accident can therefore do great injury to their neck and spine. (babycenter.com)