I've cycled thru lots of their tunnels and they're certainly scary; not lit very well and the sound of an approaching moped much less a large truck can scare the crap out of you by the sound amplification/ echo effect.
not to mention they're sometimes surprisingly long and full of carbon monoxide... i took one one when i first got here and haven't since... i was betting 50/50 on my survival, as i was sprinting my ass off to reach the end and avoid getting clobbered & got super lightheaded from sucking in nothing but exhaust for 2-3 mins.