Anger and frustration around the Ardoyne flashpoint parade in Northern Ireland should not be allowed to explode into violence, police said.
There have also been tensions around a parade today through Crumlin in Co Antrim.
A spokesman for the Order and Crumlin residents said: "The Orange Order and Crumlin Residents Association have met and participated in facilitated dialogue and have come to various agreements to ensure a positive and peaceful twelfth parade in the village of Crumlin."
Orangemen celebrating the 12th of July Protestant holiday will walk past Ardoyne shop fronts in North Belfast today. There are three other protests and demonstrations by loyalists and nationalists planned within hours of each other in the same inner city area where republicans and loyalists live cheek by jowl.
Last year officers fired baton rounds and used water cannon during hours of riots at the sectarian impasse during the culmination of the loyal order marching season.
This year Orangemen have been ordered to march past by 4pm - and police have vowed to rigorously enforce the ruling.
PSNI assistant chief constable Will Kerr said: "Listening to the groups over the course of the last week there is a lot of anger and frustration and a lot of concern being voiced by both communities about various elements of the (Parades Commission) determinations."
He added: "We understand those concerns."
He appealed for civic leaders to ask for calm and said he did not want to visit injured officers in hospital.
The Parades Commission, which rules on contentious parades, has decreed that Orangemen return from their main demonstration by 4pm today. There is a republican march planned at 5.30pm in the same area.
Mr Kerr said they would uphold the Commission's determinations on the two parades.
Last year there was serious violence in the area.
Mr Kerr said: "There is no such thing as an inevitability of violence."
He said the cycle of violence for two or three days a year threatened to undermine massively good work done during the rest of the year and pointed to the improvement in overall crime levels, at a 14-year low, and Northern Ireland's efforts to attract more tourists.
He said trouble could mean less jobs and that was not what any community wanted.
"It is absurd to assume that people can come out every year in this predictable cycle and expect for two or three days they can riot without consequences.
"The consequence is they will be caught and will go to jail. If they are looking to get a job this has long term consequences and people need to understand that before they pick up the stone or brick."
He said police had adequate resources to deal with trouble from wherever it came and said he could not see any circumstances where Chief Constable Matt Baggott would override the Commission's determination.
Parading last year cost the police service £5.7 million. There were 59 arrests in July in the Ardoyne area.
The chairman of the Police Federation, Terry Spence, who represents almost 7,000 PSNI officers from the rank of constable to chief inspector, appealed for calm and restraint at tomorrow's parade.
"Police officers will do their duty as required by the law. So should everyone else. The right to parade or to protest against a parade should not be used as an opportunity for violent and sectarian confrontation," he said.
"No yard of road is worth either an injury or the death of a police officer or a member of the public. The parade should not become a day of shame for both communities. The parade should pass with dignity and the right to protest peacefully should be respected."
Northern Ireland Secretary Owen Paterson said enormous advances had been taken in securing jobs in Northern Ireland and also appealed for calm tomorrow.
"The consequences of breaking the law would not only be bad for Northern Ireland, its global reputation and attractiveness as a place to visit and do business," he said.
"It would also be immensely damaging for anybody who engages in a few moments of madness, as the recent very stiff sentences handed down to people who participated in violence last year demonstrate."
Stormont justice minister David Ford called on politicians and community leaders to continue to use their influence for a trouble-free Twelfth.
"There is no such thing as recreational rioting. Those who take to the street to cause trouble must recognise the possible personal consequences of what they do," he said.
The Orange Order holds its main Belfast demonstration, which commemorates King William III's 1690 Battle of the Boyne victory over Catholic King James II, at Barnett's Demesne, five miles away from Ardoyne. July 12 is the culmination of the loyal orders' traditional marching season.
Previously the Ardoyne feeder parade has passed through the sectarian interface on its return from the main field at about 7pm. For years rioting has broken out afterwards.
Last year many police officers were injured after petrol bombs, fireworks and stones were hurled at them by a large crowd of republican youths close to the shops. The protective clothing of two officers was set alight when they were hit by petrol bombs. Police used non-lethal plastic baton rounds, water cannon; heavily-armoured vehicles and riot officers with large shields, helmets and batons in response.
Orangemen have complained the 4pm deadline for the parade to end will not allow them enough time to participate in ceremonies at Barnett's Demesne.
A counterprotest by nationalist residents holding placards in front of the shops is expected at the same time. Later the same evening there will be a procession by the Greater Ardoyne Residents' Collective, a republican group which opposes the march. Its demonstration last year descended into violence and pitched battles with police. This year loyalists are holding a protest at the same time.
The four groups will descend upon a small area of the inner city close to several sectarian flashpoints. There have been tensions in Ardoyne in the run up to this year's parade and argument between various representative organisations.
Three mediators, former Stormont Assembly speaker Lord Alderdice and clergymen the Rev Norman Hamilton and Fr Gary Donegan, have been exploring the scope for a peaceful solution. They have claimed to have made significant progress but admitted no agreement was reached.
Loyalists spent years engaged in violent standoffs with the security forces in hopes of regaining lost ground after some parades were curtailed following nationalist resident group pressure but eventually gave up.
The Crumlin Road beside Ardoyne is the only remaining parading point in Belfast that inspires recurring violence. There, the Orangemen have no obvious alternative way to march from their lodges to central Belfast and back. Sinn Fein has suggested they disperse at the demonstration field and do not parade home again.
In 2005, IRA dissidents opposed to that organisation's ceasefire first turned Ardoyne into the major July 12 sectarian flashpoint. They hurled homemade grenades at police from Ardoyne shop rooftops, wounding more than 100 officers.