Many rail-to-trail projects generate large economic benefit through increased tourism, reduced costs (no tunnel/train costs), improved health, select infill development (retail, housingc etc) and improved health.
In one prominent example, NYC's Highline initially had a benefit/cost ratio of 2x but this has been revised upwards to almost 4x. This is a major financial benefit.
SANDAG should conduct a formal economic analysis of rail to trail conversion to better inform public debate.