Vacuum chambers are generally safer because they don't explode; they implode. Also, the maximum pressure differential is quite low, by definition, around 14psi.

Vacuum chambers are generally safer because they don't explode; they implode. Also, the maximum pressure differential is quite low, by definition, around 14psi. Although if your traveling at 500mph towards a section of tunnel which has deformed in any way your are pretty screwed.