HM Inspectorate of Constabulary in Scotland (HMICS) was charged with carrying out an urgent review of procedures following the death of Ms Bell, 25, and her partner John Yuill, 28, in a car crash on the M9 near Stirling in July.
Police took three days to follow up a reported sighting of their wrecked car.
Mr Yuill died in the crash and although Ms Bell, who had a five-year-old son Kieran Burt, was conscious when officers arrived at the scene she died four days later in hospital.
HM Inspector of Constabulary Derek Penman said staffing levels at the Bilston Glen contact, command and control centre – where the initial call regarding the fatal crash was received – were insufficient and had resulted in “low levels of performance”.
As well as problems with staffing, the report also highlighted concerns regarding the IT system and staff training.
Mr Penman said: “I have highlighted a number of weaknesses in Police Scotland’s approach to the roll-out of its new national call handling model.
“This model is a critical element in the delivery of front line policing and a key part of the bringing together of Police Scotland post-reform.”
But he added: “The oversight of this project has been inadequate with key risks and other issues not being identified or highlighted to senior managers.”
Kieran’s father Lee Burt and the boy’s grandfather James McMillan said: “Today’s report delivers a damning indictment on Police Scotland’s call handling processes. Lamara Bell was not an isolated incident, despite what they wanted everyone to believe.”
In a statement released by lawyer Aamer Anwar, they added: “It is clear that Police Scotland was not ready for national changes in call handling but went ahead despite concerns for safety and introduced ‘unacceptably high levels of pressure’ on staff.
“Of course human error is inevitable, but the fact that Police Scotland does not even have ‘systematic processes for recording adverse incidents or near misses’ suggests a dangerously cavalier approach to such incidents. Sadly it took Lamara’s death to expose a systemic crisis at the heart of the call handling system.”
They said Kieran is “at the heart of this tragedy”, describing him as boy who “never stops speaking about his mum”.
The statement said: “Some mornings he will wake up a happy boy because he dreamt of Lamara, but it is heart-breaking when a little boy tells you he misses his mum and the sound of laughter changes to silence.
“Kieran’s family will try their best to fill his life with love but they will never be able to fill the void left by Lamara.
“The family have two primary concerns, the first is that such a catastrophe should never happen again, but second is the question of accountability.
“Police Scotland are guilty of failing communities across Scotland, whilst their approach to the complaints of call handlers can be described as at best ‘ad-hoc’ and at worst ‘shambolic’.
“Lives still remain at risk and if the authorities genuinely care about Kieran’s loss and what happened to Lamara, then they must hold to account those in the leadership of Police Scotland who appeared to have had such a reckless disregard for public safety.”