Introduction: The objective was to study the operational impact of an intervention comprised of simultaneous process improvements to triage, patient inflow, and physician scheduling patterns on emergency department (ED) patient flow. The intervention did not require any increase in ED resources or expenditures. Methods: A 36-month pre-/post-intervention retrospective chart review at an urban community emergency department from January 2010 to December 2012. The ED process improvements started on June 6, 2011 and involved streamlining triage, parallel processing, flexible nurse-patient ratios, flexible exam spaces, and flexible physician scheduling. The main outcomes were ED length-of-stay (LOS). Secondary outcomes included time to physician-initial-assessment (PIA), left-without-being-seen (LWBS) rates, and left-against-medical-advice (LAMA) rates. Segmented regression of interrupted time series analysis was performed on Canadian Triage and Acuity Scale (CTAS) 2 to 5 patients to quantify the immediate impact of the intervention on the outcome levels, and whether there were changes in the trend between pre-intervention and post-intervention segments. Results: 251,899 patients attended the ED during the study period. Daily patient volumes increased 17.3% during the post-intervention period. Post-intervention, for CTAS 2-5 patients, there was a reduction in average LOS by 0.64 hours (p<0.001), and 90th-percentile LOS by 0.81 hours (p=0.024). When separated by acuity and disposition, there were reductions in LOS for non-admitted CTAS 2 (-0.58 hours, p <0.001), 3 (-0.75 hours, p <0.001), 4 (-0.32 hours, p=0.002), and 5 (-0.28 hours, p=0.008) patients. For secondary outcomes, there was a decrease in overall average PIA by 43.81 minutes (p<0.001), and 90th-percentile PIA by 91.39 minutes (p<0.001). LWBS and LAMA rates decreased by 35.2% (p<0.001) and 61.9% (p<0.001), respectively. Conclusion: A series of process improvements meant to optimize flow in the ED without the addition of resources was associated with clinically significant reductions in LOS, PIA, LWBS and LAMA rates for non-resuscitative patients.