I deliver every cake on my lap, even 3 tier wedding cakes, while my husband drives. no problem if you shift weight and lift around turns. FROM your photo, what happened was a person holding the cake not tightly and a quick break job... cake slid apart and went down hill from there. I use SPS
Happened to me once when I let someone pick up cake and put it in there back seat, cake slid apart..on a turn. Never again...for me after that..