Introduction: Emergency Department Systems Transformation (EDST) is a bundle of Toyota Production System based interventions implemented in two Canadian tertiary care Emergency Departments (ED) between June 2014 to July 2016. The goals were to improve patient care by increasing value and reducing waste. Longer times to physician initial assessment (PIA), ED length of stays (LOS) and times to inpatient beds are associated with increased patient morbidity and potentially mortality. Some of the 17 primary interventions included computerized physician order entry optimization, staff schedule realignment, physician scorecards and a novel initial assessment process ED access block has limited full implementation of EDST. An interim analysis was conducted to assess impact of interventions implemented to date on flow metrics. Methods: Daily ED visit volumes, boarding at 7am, time to PIA and LOS for non-admitted patients were collected from April 2014 -June 2016. Volume and boarding were compared from first to last quarter using an independent samples median test. Linear regression for each variable versus time was conducted to determine unadjusted relationships. PIA, LOS for non-admitted low acuity (Canadian Triage and Acuity Scale (CTAS) 4,5) and non-admitted high acuity (CTAS 1,2,3) patients were subsequently adjusted for volume and/or boarding to control for these variables using a non-parametric correlation. Results: Overall, median ED boarding decreased at University Hospital (UH) (14.0 vs 6.0, p<0.01) and increased at Victoria Hospital (VH) (17.0 vs 21.0, p<0.01) from first to last quarter. Median ED volume increased significantly at UH from first to last quarter (129.0 vs 142.0, p<0.01) but remained essentially unchanged at VH. 90th percentile LOS for non-admitted low acuity patients significantly decreased at UH (adjusted rs=-0.24, p<0.01) but did not significantly change at VH. For high acuity patients 90th percentile LOS significantly decreased at both hospitals (UH: adjusted rs=-0.23, p<0.01; VH: adjusted rs=-0.21, p<0.01). 90th percentile time to PIA improved slightly but significantly in both EDs (UH: adjusted rs=-0.10, p<0.01; VH: adjusted rs=-0.18, p<0.01). Conclusion: Persistent ED boarding impacted the ability to fully implement the EDST model of care. Partial EDST implementation has resulted in improvement in PIA at both LHSC EDs. At UH where ED boarding decreased, LOS metrics improved significantly even after controlling for boarding.