A survey finds many officers find their job "very or extremely stressful" and they are being exposed to "increased risk".
Budget cuts are putting the police and public at risk as more and more officers are forced to work alone, according to the Police Federation.
A survey for the organisation, which represents rank and file officers in England and Wales, suggested almost 90% of respondents believed there were not enough of them to manage demand, while 76% of officers in front line roles were "often or always" working alone.
It also found that of the 18,000 who took part, almost every officer had been exposed to at least one "traumatic experience" in their career, with 62% saying they had experienced at least one in the last 12 months.
Police Federation national vice-chair Che Donald said: "When officers work alone they are undoubtedly exposed to increased risk, for them and the public, not to mention the detrimental effect on their overall health and well-being."
He added: "Forces are having their hands forced as they struggle to meet the increased demands placed on them, but this false economy of single crewing merely creates the illusion of public safety.
"Quite simply this is not sustainable and officers are suffering."
Mr Donald said that since 2010, cuts meant that there were 22,000 fewer officers and that the "once revered British model of policing is currently on its knees and facing extinction".