Personally, I do like the idea of a raised railway line being built across the Sahara, just because I love a good MegaEngineering project.
But it isn't going to work without substantial stations along the route - where the Tuaregs are going to be able to benefit from it.
Perhaps working with the Tuaregs to perform some sort of resource survey so that they can scout out good points for mines or quarries (or whatever else could be exploited) and setting these up as actual settlements where Tuaregs could get involved in the business, as well as transport - and which alongside encouragement and other deals - would create a local incentive to protect the railway.
"You mean that iron horse can move rocks that you'll pay me WHAT?! for? Fantastic, hurrah!"
"Wait, you have machines that I can dig how many emeralds out of the ground with?"
"Hmm, I like this opium, its very nice"
Obviously quarries will ONLY work if there are trains, but other resources that the Tuaregs could transport initially could create some incentive to protect new train lines. Admittedly, those doing the transport will need to be brought into the train services otherwise there is a conflict there.
The problems is that touaregs were traders, mostly interested in transporting stuff (including slaves) from one point to another with no mining industry or anything. That said I do like the idea of opium. Worked for the chinese, might work for the touaregs. Very devious though
Quite the opposite, it is said that the camels are the ones that scare horses. Note that even that may be a myth with no basis in reality (other than some horses possibly being scared by unknown animals bigger than them the first time they encounter them).
Sadly it is a long time since I last staged gladatorial combats with animals fighting each other so I don't really remember. I'm just quoting the report here, I assume they know what they're talking about but feel free to counter-source me, any knowledge is welcome
I'd like to expand on my initial post by saying that it really wouldn't have been that cost effective without something in the interior to take advantage of.
It could help in constructing earlier oil field pipelines, but I'm not even sure that this railway would be faster than shipping by boat after transporting goods to the coast.
Well there is a ton of mineral there, even if most of it is discovered later. Coast is not always an alternative cause you got to build the infrastructure to bring the goods to the coast. So no matter what, you end up building a railway, might as well build one that ends up on your side of the continent.
Plus the idea was to make it easier to colonise, and I think here we touch the most interesting possibilities. You could use the fertile lands to do agriculture, use the railway to transport water and create oasis and bore wells more easily, basically a variation of "turn the Sahara into a garden" sort of things. So the fruits would not come quite away but it was a long term project to transform inner West Africa in something actually profitable in term of tax revenues and production