Agree regarding the consequences of a bus bridge episode. Even light rail in an urban transit system can be a problem when a breakdown requires a bus bridge at rush hour when essentially everything usable and all drivers available are in service. Have experienced delays of 2 hours or more (to what should be about a 1-hour trip) in those circumstances, even if all affected trains are able to halt in stations (which are usually less than a mile apart). Also, most light rail lines are not far from roads, often running in or alongside major roads; buses have fairly easy access to any point on the line.

SMART doesn't fit those criteria: it's well away from major roads at many if not most points, stations are a mile or more apart (usually more). And it's not part of an urban transit system where no point is more than an hour or so from a dispatch yard once drivers and buses are activated. Stranding passengers out in the salt marsh between stations could be a serious issue requiring emergency response, not just a bus bridge.

IOW, the trains have to work. Period.