From a Physics Point of view - the solid object at 100km/h would be less impact and force than 2 cars of equal size/weight/speed hitting head on at 100km/h.
Inertia is what the big factor is....
one stationary object, and one travelling at speed of 100km/h
vs
two identical objects travelling towards each other at 100km/h
you can have all the crumple zones / airbags / safety features that you like....
but at the end of the day - the PHYSICS answer is that the 2 cars head on will be worse than hitting a solid object at 100km/h.
My old man wrote the book on Yr11 & Yr12 Physics (literally -
http://www.seekbooks.com.au/book/Phy...0701637811.htm)
It is used in 90% of schools in Australia... He knows his stuff....
I've chatted to him, and he also agrees with the above...