Women-only tube carriages

Do these protect women from sexual assault or harassment?  Or do they cause women to change their behaviour to avoid victimisation, instead of teaching men not to be perpetrators?

How will they be policed?  How can they stop men from entering women-only carriages?

What about women who feel safe enough to enter mixed carriages, or need to because of lack of space – are these women asking for it if they do get harassed?