they are quite a bit different. yes you can get lucky and find the perfect mellow rail with natural speed in run and the snow packs really well for the take off. but that isnt too common.
most of the time youre dealing with a slow in run that you have to use a drop in ramp/bungee/hand pulls whatever to get speed. the speed will usually be inconsistent and the in run wont stay as nice as it usually does in a park.
urban rails are generally higher. sure you can build a tall ramp up onto it but thats cheating and when youre actually on the rail youre going to be higher off the ground. if you come off early watch out for everything and anything to stop you or make you crash. in a park you can just hop off early and ski off to the side, not so much with stairs/rocks/trees around you.
the painted/sticky rails shouldnt be that big of a consider. you can use your edge to scrape any ice/paint off the rail before hand and then it should be slick enough.
i dont want this to discourage anyone because hitting street spots is a lot of fun when it goes right. the key points i would suggest you focus on are
1: find a low and mellow rail for your first. flat rails are actually more difficult because you will need more speed to balance. a nice 10-15 stair rail that isnt very steep is optimal.
2: take time to build a good in run and take off. you want to make sure the lip isnt going to give way when you go to pop on. also note building a higher lip may seem like the best way to make it easier, a higher lip will just take away speed from you. when youre jumping on to the rail, youre not jumping up to it right next to you. youre jumping out and down the rail. so if you have decent speed you dont need a very high lip at all.
3: if someone kicks you out be polite and do as they ask. even if they are being ridiculous.
4: clean up the spot when youre done.
