Possibly. I guess it's hard to know operation costs of RER at this point since it's yet to be implemented. And there seem to be different ways of going about how costs can be presented, whether they're presented line-by-line, or if they're presented at all.
One thing that could reduce RER's op costs compared with underground subways is manned vs unmanned stations. It's probably a drop in the buck in the grand scheme of things, but it's my understanding that with an underground station it's mandated by law that at least one personnel has to be onsite during operating hours. With an open-air platform like GO/RER that's obviously not needed.
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