Level-load retrieval time: a new criterion for EMS facility sites.

A new optimization criterion for locating emergency medical care facilities, level-load retrieval time, is described and applied to Los Angeles County. Results are compared with those obtained by optimizing mean retrieval time. The new cirterion combines retrieval times from demand points served by each facility and patient load on each facility; it yields facility sets with average retrieval times 5 to 10 percent longer, but with much more uniform patient loads, than the sets obtained by optimizing mean retrieval time. The new criterion can be used as a complement to other planning criteria and may help reduce excessive demand on the emergency care services of overloaded facilities.