An ageing fleet, high sickness rates and slow uptake of technology hampers the ability of the NHS to answer 999 calls quickly, a review says.
The report produced for the regulator NHS Improvement found significant inefficiencies in England.
If the problems are not addressed, it will be more difficult for ambulances to hit their targets, it said.
In July eight out of 10 services missed their seven-minute target for answering the most life-threatening emergencies.
'Simply unacceptable variation'
Lord Carter, an expert in NHS productivity who carried out the review, called for an overhaul in approach.
"An ambulance is not a taxi to A&E. Modern technology means that patients can often be treated at the scene.
"But an ageing ambulance fleet means that this is not always possible."
The review found:
- The ambulance service had the highest rate of sickness in the NHS – 20 days per person
- High levels of bullying and harassment
- Auto-dispatch technology to speed up responses to cardiac arrests was not yet fully implemented 12 years on
- Use of digital technology to access patients records is in its infancy
- One in four ambulances was more than seven years old – the point at which annual maintenance costs start rising quickly and reliability deteriorates
- A 50% difference in costs between the most economical and least economical trusts per incident attended
- Significant differences in the proportion of patients being treated at the scene
- No fewer than 32 different types of ambulances – something the report said was "simply unacceptable"
The review said tackling the problems identified could save £500m a year by 2021 – money that could then be reinvested into services.
Lord Carter said: "Paramedics and other staff have worked incredibly hard as demand for ambulances has soared.
"It is now vital that improvements are made in the infrastructure of the wider NHS to help front-line staff work as efficiently as possible."
The report said demand was predicted to increase by 38% over the next 10 years.
Martin Flaherty, of the Association of Ambulance Chief Executives, said it was clear improvements could be made.
But he also pointed out that some of the variation was down to "local geography and patient demographics".
And he said the availability and performance of other parts of the NHS also had an impact on ambulance performance.
The report echoed this too – calling for more progress in extended GP opening hours and the availability of minor injury units, as well as help from hospitals in reducing the delays at A&E when paramedics hand over patients.
The government said it was investing in the NHS, pointing out £36.3m was provided earlier this year to fund 256 new ambulances.
This is on top of the extra £20bn a year that is being invested in the health service by 2023.