With key Access Regulations you usually need to apply for a permit - if you meet the requirements.
If you don't meet the requirements, then you are not allowed access.
Some access regulation schemes require prior registration for those that are allowed entry, examples include the Italian ZTLs, Prague, Helsinki, Bucarest amongst many others.
Other access regulations are simply indicated by the road signs, which you need to comply with. Examples of these include the access regulations in Bulgaria, heavy duty vehicle transit bans Germany and Latvia.
See the Overview of key Access Regulations for an overview of the registration requirements, or or the individual city page for full details.