quicko: the harbour tunnel

So there is a huge tunnel under the Sydney Harbour, rather predictably, for traffic.  I really dislike taking it, partially because it means you can't go over the bridge and see the pretty harbour (a friend once driving me into the city asked if we should take the bridge or the tunnel.  "The bridge!" I exclaimed, happily.  "Kim," she said.  "You know this isn't purely an aesthetic choice, right?").  However, the other part of the problem is that universal difficulty that tunnels beneath bodies of water could -- could -- at any moment give way and crash, filling themselves with water and leading to the prompt and painful death of anyone within, namely, when I am within them, me.  Thus, I have asked around and developed this handy plan to help:  (ahem) instead of trying to remember the distance and how far in you are (and which way is closer for escape, should escape become necessary), in the Sydney Harbour Tunnel, it is necessary only to look at the walls and see if you are angling down or not.  To escape, simply swim UP!  You might still die, but at least you'll die trying, hey?

Never hurts to be prepared, eh, boy scouts?