Escaping from a modern jail is possible but it's also not very easy.
Modern Jails have several security measures and doors to prevent escape and cameras are all around as well.
The modern jails also have doors that separate the inmates from the local lobby area and the regular door that remains open.
So you cannot just walk out of the jail because you have to get past the security door.
Also in the night the inmates are locked down in their jail cells to prevent escape during the night.
The same is true with prisons as the inmates in the prison are locked down and counted to ensure they are in the cells.
Then in the morning the inmates are counted again at a certain time.
So escaping from modern jail or modern prison is possible but it's very hard now.