Up to 200 police officers are needed to provide security at interfaces across Belfast on a nightly basis.
Tensions have escalated to such a degree that a continued police presence is necessary to prevent outbreaks of violence in several areas, particularly in the north and east of the city.
There is concern within the PSNI and the Policing Board that resources are being tied up at interfaces at a time when police officer numbers are at an all-time low.
"If we weren't out there at these interfaces somebody could end up seriously injured. But it does mean that officers are being taken from other duties to maintain a presence in these areas," one PSNI officer said.
Policing Board member Jonathan Craig said: "It is a major concern that there are several interface issues across Belfast. It is chewing up massive resources and costing a fortune."
There are around 100 identified interface areas across Belfast. While many remain peaceful, there are some where violence can often erupt.
Last month three police officers were injured during three consecutive nights of sporadic trouble near an interface in the east of the city.
The most expensive interface policing operation is currently at Twaddell Avenue in north Belfast, where Orangemen have been holding a nightly protest camp over a Parades Commission decision to ban them from marching past the nationalist Ardoyne.
The police operation at the protest camp has so far cost over £7m.
Dr Jonny Byrne, a lecturer in criminology at the University of Ulster, said that major political events in recent years, such as the flag row and the failed Haass talks, have manifested into situations of public disorder.
Dr Byrne, who has carried out several studies on interface violence and peace walls, warned that the issue cannot be resolved by the PSNI.
"All that officers can do is provide a presence at these interfaces to reassure the public and to discourage outbreaks of violence. In some serious cases they are the physical barrier between two groups," he said.
Dr Byrne added: "This cannot be left a policing issue. This has to be addressed by communities themselves.
"We have travelled a great distance in the past 10 years. We do not have the same organised and continuous levels of violence that we used to have. That is down to a lot of hard work in communities to address this issue. It is only small pockets compared to what it used to be. But the problems are still there."
Some of the main interface areas include: