Could you quote a transitive usage of it? I really can't fathom anything right now.
Here:
夜明けにたったひとり列車を降りて。 Step off the train all alone at dawn.
坂を下りるときに...
彼女は 乗客がバス を 降りるの を 見つめていました。She watched the passengers get off the bus.
There are also usages with で and に。
The same thing is with 流れる verb. It has a transitive pair 流す, but here is the right particle from JLPT test:
長江はちゅうごく を ながれています。
My world is shattered. What's going on? :(
Verbs of motion can take を even if they are intransitive.
https://japanese.stackexchange.com/questions/21313/why-does-%E5%87%BA%E3%82%8B-accepts-%E3%82%92-although-it-is-an-intransitive-verb
https://japanese.stackexchange.com/questions/12734/it-seems-that-%E6%B8%A1%E3%82%8B-is-categorized-as-%E8%87%AA%E5%8B%95%E8%A9%9E-intransitive-verb-yet-it-is-frequently
降りる / 下りる - intransitive or transitive or both?
Correct me if I'm wrong, as I get it 降りる is for vehicles like trains and buses, and 下りる is for high grounds like stairs and mountains. From examples you can see both transitive and intransitive usages, so shouldn't this be fixed in the description?