OHHH God. haha street downrails scare the living crap out of me, i have done 3 in my life, i did one like 4 times, but a few close calls has me waiting til i get a helmet. I dont wanna end up paralyzed from something like that. One is awesomely low but quite long and high at the end and it moves if you hit it hard in any way so there is no room for error really, another was very scary because going up to it is very intimidating because there are 3 stairs right in front of the rail that you gotta drop then hop immediately, it was a flat rail and i did that one because i was really on one that day haha, but i dont think i could muster up the balls again really til i get a helmet because of the last one. This one was kinked at the very end and i had never done one before, i made it down the rail my second try, the first try was very very scary because i lost my footing and my bike came out and i hit my nuts and face. Not fun. I HAD to get up and do it again because if i dont land something i have to get up and do it again til i get it, but i havent done a street down rail since, i promised myself i had to get a helmet. And yeah, the trick is to get that rear peg on and keep your weight over the rail, i tend to hop really high so i dont have to worry about it as much. dont fly at it, you will get a lot of speed going down too, and pull up and lean back a bit at the end so you dont land in a nose dive (depending on the rail) if the rail is low, you really dont have to worry about coming off, you may just roll right off. haha
References: OneGuyIlluminatiEye, robinson79, Brian Griffin, The Horror Contact, StoreBoughtChild, C_Johnsonbmx, dkTechEthan, etc.