The parents of teenager whose death has caused international controversy have met with NHS ambulance bosses to raise "concerns" over its response time.
Harry Dunn, 19, died in hospital after the crash in rural Northamptonshire in August. The suspect left the UK claiming diplomatic immunity.
The first East Midlands Ambulance Service (EMAS) staff arrived 41 minutes after the start of the 999 call.
His parents were told at a meeting the nearest available resource was sent.
Mr Dunn's motorbike crashed with a car owned by US citizen Anne Sacoolas, the 42-year-old wife of a diplomat, outside RAF Croughton, near Brackley, on 27 August.
His mother, Charlotte Charles, and father, Tim Dunn, are campaigning for justice after Mrs Sacoolas returned to the US, claiming diplomatic immunity, shortly after the crash.
Northamptonshire Police has handed a file to the Crown Prosecution Service after interviewing the suspect in the US.
The emergency call for the crash was made at 20:25 BST and, as Mr Dunn was conscious and breathing when the 999 call came, it was graded as category two,
Guidelines state those calls should be responded to at least nine out of 10 times before 40 minutes.
A doctor, who was dispatched within two minutes, arrived 41 minutes after the start of the 999 call, and an ambulance arrived two minutes after the doctor.
Mr Dunn was transferred to the Major Trauma Centre at the John Radcliffe Infirmary in Oxford but was later pronounced dead.
Richard Henderson, chief executive of EMAS NHS Trust, said after the meeting: "I wanted to take the opportunity to hear from the family at this stage, whilst recognising the complexities and sensitivities of ongoing external legal investigations.
"I understand this is a very difficult time for the family and I therefore appreciate the time I had with them."
Mr Dunn's family's spokesman, Radd Seiger, said the parents were "incredibly grateful to all the staff who worked tirelessly to save Harry's life that night".
He added: "We had a very warm and constructive dialogue with a view to shining a light on the many challenges which the service faces and which are likely to have played a part in the delay on the night of the collision.
"The parents were able to express their concerns to Richard and Nichola [Bramhall, director of quality] in a positive way with a view to working together to hopefully ensuring no other patient suffers the terrible fate that Harry did."