According to Liverpool's Historic Rail Tunnels (http://www.liverpoolwiki.org/Liverpool%27s_Historic_Rail_Tunnels), the world's first railway tunnel was the Crown Street Stephenson Tunnel of 1829. Should the introduction date of RailTunnelStone (in tunnels.dat) be changed to 1829, and RailTunnelBrick to something like 1848, the date of the Victoria/Waterloo Tunnel mentioned there?
Sounds fair enough to me.
Excellent research!