People have survived (badly injured) in real life. Being crushed in a garbage truck is very dangerous but can be survivable depending on how much and what sort of garbage is in there, when the victim gets rescued and what medical care they get afterward. Also Shredder is a movie supervillain in armour so he is stronger and better protected than the average person.
Answer: He didn't escape. He just managed to survive somehow. Hence, we see him escaping at the dump after the truck drops off the garbage.
TedStixon
Then how exactly was he not crushed while inside a garbage truck?
Athletic Jason
People have survived (badly injured) in real life. Being crushed in a garbage truck is very dangerous but can be survivable depending on how much and what sort of garbage is in there, when the victim gets rescued and what medical care they get afterward. Also Shredder is a movie supervillain in armour so he is stronger and better protected than the average person.