The major indication for Lights & Sirens (L&S) is a presumed significant decrease in response and transport time. However, multiple studies reveal a minimal decrease in transit time with L&S use, with an average of 1.7 to 3.6 minutes saved.

For most conditions, EMS providers can provide timely care on-site or en route to diminish the importance of time saved by L&S transport, thus reducing the risk to providers, patients, and the public. In greater than 90 percent of patients, there is no improved outcome from L&S use. For some conditions, such as ST-elevation myocardial infarctions, trauma with life-threatening haemorrhage, obstetrical emergencies, or ischemic strokes, the use of L&S use may improve patient outcome by decreasing transit time. However accurate prehospital notifications to the receiving hospitals may be more beneficial than L&S as this should reduce in-hospital delays waiting for therapeutic interventions. In some cases, prehospital notification has shown an evidence-based improvement in patient outcome by mobilizing the necessary resources.