This was an implementation problem for this game before it was moved to the new map collection. The rules say:
The colored cards are more valuable here so forcing a player to use them for the revealed cards potentially messes up their gameplay if they were saving some for another route and now used them all when they expected to be able to use the locomotives for any extra cards. I've had to adapt my gameplay on this board in order to get around this issue. I shouldn't have to plan to claim a less important route first just because the tunnel route is going to eat my colored train cards when if I could use a combination of colored train cards and locomotives I'd be fine.
It is high time it gets addressed! There is an issue logged but the developer has called it Not a Bug, please vote for it and comment on it so we can play as we were meant to for this board without having to play through these constrictions.
https://boardgamearena.com/bug?id=192141
Therefore the player should be able to select any combination of colored train cards and locomotives to play for a tunnel route. And again for the further revealed cards.Locomotive cards complement or replace the colored cards required to claim a Tunnel route, but they can never be used to help claim a regular (non-Tunnel) route.
For each card revealed whose color matches the color used to claim the Tunnel (including locomotives), an additional card of the same color (or a locomotive) must be played to successfully claim the Tunnel.
The colored cards are more valuable here so forcing a player to use them for the revealed cards potentially messes up their gameplay if they were saving some for another route and now used them all when they expected to be able to use the locomotives for any extra cards. I've had to adapt my gameplay on this board in order to get around this issue. I shouldn't have to plan to claim a less important route first just because the tunnel route is going to eat my colored train cards when if I could use a combination of colored train cards and locomotives I'd be fine.
It is high time it gets addressed! There is an issue logged but the developer has called it Not a Bug, please vote for it and comment on it so we can play as we were meant to for this board without having to play through these constrictions.
https://boardgamearena.com/bug?id=192141