Please send me your log file and screenshots of your graphic settings in Omsi.
I suspect either a fault in the vehicle or a wrong setting. Does this happen on all buses or only on certain ones? And on which map do you have this problem?
PS: It makes no sense to compare OMSI with other games in terms of performance because OMSI A) is shitty optimized and, secondly, is only based on 32-bit.
The second is the main reason why OMSI can never use the full power of your PC.
32-bit is limited to 4 GB of RAM, which is why Omsi can never use it again, even if you have 8, 16 or 32 GB of RAM.