The newest tunnels have lights installed but they are switchable, so depending on what else is going on in the tunnel they may be on or off. The Channel Tunnel for example has pretty bright lights installed, but more often than not they are off.If you watch some of the many driver's-eye view YouTubes from Europe, it seems like newly-built tunnels usually are lighted.
Pretty sure I've seen YouTubes of dark stretches in the maze under downtown Brooklyn. I don't know whether there were no lights, or they were there but not working.I can't recall any subway tunnels in the USA that are NOT lit. Most are quite dimly lit, though. For emergency purposes, once one's eyes are acclimated to the lower light levels, it should be sufficient to exit the tunnel in an emergency.
Speaking of things that would likely not be built today! I had forgotten how long that tunnel is - and seeing how creepy and narrow the first set of single bores are when not viewed from a coach.Cab ride in an AMT Electric MU from Montreal Central Station thru the 3 mile Mont Royal Tunnel. The tunnel is now being converted for use by the new REM Light-Rail.
(Just click.....watch on Youtube to view)
Speaking of things that would likely not be built today! I had forgotten how long that tunnel is - and seeing how creepy and narrow the first set of single bores are when not viewed from a coach.