The Africa trade route upgrade ‘caravan trade’ has a speed of 7, and the ‘Trans-Saharan trade’ upgrade goes up to 8.50 speed, which is out of place since it would not be a railroad.
Why not just increase the delivery rate and leave the speed of 7 for the ‘Trans-Saharan Trade’ upgrade? It would make more sense since it would be camels.
You could also change the stagecoach for the camel track.