No, really. The T-S Railroad was a serious project, and it could have happened.
It was -- if you were French -- an obvious idea: run a rail line south through Algeria to sub-Saharan Africa, all the way to Timbuktu on the Niger River, then southwest to Bamako and eventually, Dakar. You'd avoid the long run around through the Atlantic (dominated by, ahem, the Royal Navy). You'd be able to bring trainloads of stuff from the Sahel and the upper Niger valley straight up to the Mediterranean. Dakar would be just a few days from Marseilles!
It was first proposed in the 1870s, and popped up again every couple of decades. Got seriously considered in the early 1900s; reached the Parliamentary study-and-report stage in 1928. Got within arm's reach of actually happening then, but the Great Depression intervened. Then in 1941, the Vichy government decided to build it to show that France was still, you know, virile and stuff. They actually laid a few miles of track before Vichy closed up shop.
In between, some bits actually got built: a line from Oran south to Colomb-Bechar, deep in the interior of Algeria, and another line north from Dakar to Bamako in what's now Mali. (Both lines are still in use today.) That just left a couple of thousand kilometers in between. Okay, a couple of thousand very hot, rocky and sandy kilometers.
So let's say (handwave) that the prewar Third Republic gets seriously interested in this. The Italian invasion of Libya is a precipitating incident -- OTL the French were more than a bit annoyed by this -- and ground is broken in January 1914.
Well, various things intervene, and construction is halted for almost a decade. But once the project has been started, it's going to be very hard to kill. So, more construction in the 1920s, a pause for the Great Depression, then a final effort in the 1930s, with a golden spike somewhere in what's now southern Mali in 1937.
Now what?
-- There's no way this thing is ever going to make any money. Maintenance costs are going to be off the scale. Parts of Senegal are suitable for plantation agriculture, but that will still go out by Dakar. Mali can produce dryland crops and meat from herds, but those either won't produce much profit or won't travel well. Irrigation agriculture for export on the upper Niger is probably a non-starter. Mineral resources, there aren't a lot besides rock salt. (Really.)
But hey, la gloire.
And then in 1940, there's a direct land connection from Vichy French North Africa to Dakar.
Thoughts?
Doug M.