The tag may contain the official lenght of the tunnel or of the bridge.
See here 2 example:
1) Tunnel: https://www.mapillary.com/app/?pKey=1353553059314036
2) Bridge: https://www.mapillary.com/app/?pKey=1996202717536767
Can you explain why this information is "redundant"?

Wrong decision: dozens of lengths I'd inserted (because there is an official sign indicating the length of the tunnel or bridge) were also removed.
These massive, unverified edits cause more trouble than good.

Hi, AndreaDFC writing here. Why did you delete my tags?!?