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D.8.4.1) Ambulance Stations


There are currently eleven ambulance stations serving West Sussex:
  • Chichester,
  • Bognor
  • Littlehampton
  • Crawley
  • Durrington
  • Lewes
  • Burgess Hill
  • Horsham
  • Midhurst
  • Pulborough
  • Shoreham
SECAMB have proposed combining Midhurst, Bognor and Pulborough stations into a 'superhub' at Tangmere. I wanted to know what effect this might have on response times, focussing from the Manhood Peninsular to Brighton.


The following are the isochronal maps for time-to-travel from each station (assuming travel at 'car speed' which is slower than an ambulance but it is probably a reasonable assumption that the two are roughly in proportion). other assumptions include:
  • All locations in the county need to be accessed by ambulance.
  • Ambulances are always available at every station.
  • The dispatcher will always send an ambulance from the nearest available station.
  • The ambulances are all at stations, not deployed to 'wait' locations.

Green = 0 minute; Red = 1 hour or more. The positions were taken from Google Maps. The effects of traffic were excluded - lets assume that an "ambulance minute" is of smaller duration than a normal minute.

Burgess Hill
Burgess Hill


Crawley
Crawley


Durrington
Durrington


Bognor


Horsham
Horsham


Pulborough


Midhurst


Burgess Hill
Lewes


Shoreham


St Richard's, Chichester


At each point on the map the lowest time-to-arrival can be used to determine the station that can get to the location soonest:


The average duration of the journey is 13.0 "ambulance minutes" (remember this is not an absolute value, but can be used to compare figures with those of the super-hub). "Ambulance minutes" are of shorter duration that normal minutes.

With Midhurst, Pulborough and Bognor removed the map becomes:


The average duration of the journey is now 18.1 "ambulance minutes" or about 40% greater: however, this is mitigated by basing ambulances at Community Response Posts where ambulance crews can wait and that will be located at:
  • Arundel
  • Billingshurst
  • East Preston
  • Midhurst
  • North Chichester
  • Lancing
  • Selsey
  • Storrington
  • Westgate
  • Broadwater.
If there was an ambulance at each of these the same style of map becomes that as below:


The average time to arrive is 10.3 "ambulance minutes".

However, this still assumes that the demand for an ambulance is uniform over the whole area, which patently isn't the case and that an ambulance is always available at the nearest CRP. Ignoring any increased need for ambulances at accident blackspots, etc., the need can be assumed to be a function of the number of people.

Using data from the WSCC data the electoral wards were represented by circles having the same area as the ward, located at the approximate centroid of the ward and with the same population as the ward. This analogue is shown below:


This allowed the people in need of an ambulance to be weighted proportionately to the distribution of population. Selecting 100,000 random 'people' and investigating the time from the various ambulance stations allowed a more accurate model to be developed.

The sample points are shown in the figure below; this has a striking similarity to the above figure, with the samples biased toward the more densely populated areas.


Equally, the cumulative distribution of modelled population correlates reasonably well with the actual numbers.




The average time-to-arrive is 8.1 "ambulance minutes", this distribution being that shown below:



The distribution of the number of times that each site is the nearest to the modelled 'person' is shown below:


The second most effective place to have an ambulance (or ambulances) stationed is Bognor. Its almost as if having some some sort of ambulance station there would be a good idea...


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