Fully opened in May 2023, the Elizabeth Line is the largest addition to London’s public transport network since the Victoria Line in 1968. Operating up to 24 trains per hour with the capacity for 1,500 passengers per train, the line has transformed how passengers use public transport within London. Transport for London (TfL) operates the line and wanted to understand future demand patterns to ensure that it would run smoothly for years to come. Due to the scale and complexity of the project, they knew that spreadsheet-based models would not be possible.  TfL used OpenPaths and LEGION to assist with conceptual creation, route selection, and final delivery of an operational railway, and continue to use it for post-opening optimization. During the pandemic, EMME provided a complex crowded assignment in two hours, a reduction of 70% from previous model run times. LEGION tested iterative station designs over the project lifecycle, ensuring optimal station design, adherence to passenger safety standards, a positive passenger experience, and sufficient capacity until 2076. TfL forecasted 10 million fewer car journeys per year to transfer to the Elizabeth line, a net reduction of 24.6 million fewer grams of carbon emissions per day.