djnekkid opened the ticket and wrote:

Supermop discribed the problem quite good here:
http://www.tt-forums.net/viewtopic.php?f=26&t=47347&p=876193# p876192
Quote:
Just noticed a quirk today while slowly financing a new dedicated Very High Speed Line, converting from planning track. The cost of converting a tunnel of x tiles in length from planning to VHSR seem to be commensurate with converting x tiles of track on the surface. However, building a new VHSR tunnel rather than converting one costs the same as building one of the same length with Very Low Speed Rail without caternary. It seems all tunnels cost the same for a given length regardless of rail type, while converting incurs the regular cost. Bridges seem to display the same behavior. I don't really see it as a big problem, as anyone who might exploit this would probably not be playing with NuTracks anyway, I just thought it was odd enough to warrant a mention.

I Just tested it myself as well on r19736(win7/64bit), and it is still there.

Reported version: trunk
Operating system: Windows

This issue was imported from FlySpray: https://bugs.openttd.org/task/3827