>>1876208>they exist in sufficient numbers that they'll replace everybody in Group AThat's not the requirement. The requirement is that they exist at all. Past that point, the size of the group would be proportionate to the degree of capture Brightline can manage (increases the size), and how congestion of the corridor would expand in the no-build alternative (decreases the size). They forecasted that a consistent 50-minute delay for I-15 traffic would lead to an 18% increase in BW ridership, so the elasticity isn't terribly high, even with delay nearing 40% of optimal highway travel time, so Group B would not be large. For the purposes of ridership forecasts, they're just road traffic that doesn't get diverted, but for projects with high modal share/congestion alleviation potential, they would get more attention (if only to show stakeholders why capacity changes aren't 1:1).
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https://railroads.dot.gov/sites/fra.dot.gov/files/fra_net/166/Appendix_F_D_Ridership_Forecast_Review.pdf 