The Michigan Central Railway Tunnel is an international tunnel that connects Detroit, Michigan with Windsor, Ontario. It is an international tunnel because it connects two countries by railroad and because it was built for owned or leased by companies on both sides of the border. The Detroit River Tunnel Company (also very international – read below) built it in 1910 for the Canada Southern Railway; it was leased by the Michigan Central Railroad and it was owned by the New York Central Railroad. Are you confused yet?
It was built to give the Canada Southern Railway and the Michigan Central Railroad a competitive chance at business. In 1891 the Grand Trunk Railway opened the St. Clair Tunnel at Port Huron, giving it the business advantage.
When the Michigan and Canada Bridge and Tunnel Company and the Canada and Michigan Bridge and Tunnel Company from Canada merged on August 15, 1905, the Detroit River Tunnel Company was formed. This company began construction of the tunnel in October of 1906 under the engineering supervision of The New York Central Railway's engineering vice president, William J. Wilgus. The $8.5 million Michigan Central Railway Tunnel opened for passenger service July 26, 1910. Freight service began September 15th and on October 16th all rail traffic began using the tunnel. It is one and three eighths miles long and it is still in use today.
The above information was abridged from: http://en.wikipedia.org/wiki/Michigan_Central_Railway_Tunnel
Looking at the back of the post card we see that it was published by the Wolverine News Company out of Detroit, Michigan. The information is down the left-hand side of the post card.
The post card comes from the Divided Back Era; the Address Side is clearly labelled but it is taken for granted that the other side is the Message Side. I just noticed that under the T and above the R in POST CARD there is a logo that tells us that Curt Otto Teich printed this post card. The number at the bottom of the card (A-17410) then tells us that this was printed between 1908 and 1910.