The question of what is the effect of extra weight is easily calculated. I used Google AI to do the calculation. The results are surprising and tie up with the statistics.
How much energy is transferred to a 100kg mass when struck by a 2000kg mass traveling at 30km/h? The amount of energy transferred to the 100 kg mass, assuming a perfectly elastic collision, is approximately 12,598 J (Joules).
How much energy is transferred to a 100kg mass when struck by a 1000kg mass traveling at 30km/h?Assuming the 100kg mass is initially at rest and the collision is perfectly elastic, approximately 11478.42 J (or 11.5 kJ) of energy is transferred to the 100kg mass.
Even being by a ten ton truck is only a bit worse. The energy transferred to the 100kg mass is approximately 13615.22 J.
An elastic collision is one in which the objects after impact become stuck together and move with a common velocity. Thats a bad pedestrian crash. In all three cases the collision is probably fatal. Crumple zones help reduce the damage.
My apologies for using Google AI for every calculation.