Perhaps it was the geek in us (a love of trains as well) but tunnel advertising always excited us, although it never seemed to whet the appetite of advertisers as much as we thought it ought.
Anyway we hear movement (geddit?) on this front in Nanjing, China.
Submedia, LLC, who install in-tunnel and walking motion picture displays in a number of places† are, we hear, in the process of launching one of the first digital tunnel displays in China.
We also heard from engineers involved in the project that it is by far, the brightest display they have ever built AND it may well be a new (conversion) format for all of their tunnel displays.
† Their web site says New York; Chicago, Illinois; Washington, DC; Boston, Massachusetts; San Francisco, California; Toronto, Canada; Tokyo, Japan; Hong Kong; Prague, the Czech Republic; Istanbul, Turkey; India; Egypt; Nanjing, China; the United Arab Emirates; Taiwan; Kiev, Ukraine; Bratislava, Slovakia; Bucharest, Romania; London, the United Kingdom; and Mexico City, Mexico.