Smr Simple!

You can select what type of tunnels you want in your map and when do you want them.
The starting date and the ending date of each type (Wood or masonry) can be specified.
In the sample below constructions of the wood tunnels will stop in year 1999. The already existing wood tunnels will stay unless you redraw them.
Also the masonry tunnels will be built at shallow locations where wood was used before.
You have to add the red marked lines to C:\Users\User\Documents\My Games\Sid Meier's Railroads!\UserMaps\Mars\RRT_Tunnels.xml file.
<Tunnel>
<szName>Masonry Tunnel</szName>
<nYearStart>0</nYearStart>
<nYearEnd>3000</nYearEnd>

<Tunnel>
<szName>Wood Tunnel</szName>
<nYearStart>0</nYearStart>
<nYearEnd>1999</nYearEnd>
Jancsika

The same seems to apply to the Bridges.
If you don’t want to use certain type of bridge or tunnel you can set the date, so that it will end before the scenario starting date.
These will have to be tested, but what I’ve tried it worked.
Jancsika

Sorry if I'm necroing here, but this is exactly what I am trying to do, but cannot get it to work. I have a RRT_Bridges.xml in my map folder and for example adjusting prices works flawlessly. I have set nYearStart and nYearEnd on all bridges, starting year 0 to year 3000. I want for example only wood bridges untill 1870. What happens is all bridges is enabled from the start, when i am at 1850. Does anyone see any error or know what to do?

My RRT_Bridges.xml
http://pastebin.com/gFiFVUKp