One way streets

[dirtyoldman 0]

Streets won't "accept" changes attempted.  What is the protocol?

[beebs 129]

You need to run the one way road from intersection to intersection.. the game won't allow it to change from road/street to one way road in the middle of the road.

[SC4BOY 20]

Or delete and redraw.. not all types of transport will directly overlay another.. for example diagonal streets are no-no's for other "overdraws" . plus in some cases a "special intersection" will have to be destroyed too before you can pass through or make an intersection .. examples diagonals merging, oneways into other types, etc.. and be CAREFUL or the oneways will end up blocking traffic where you don't expect it because it didn't build quite like you thought it would.. check with the "cheat" drawpaths from the "extracheats.dll" file .. It will show arrows in most places to show continuity of traffic flow.

[elusive.aria 1]

To add to what beebs said, I have also found that it is not possible to drag a One-Way road from/to an intersection which currently involves BOTH a street and a road. A four-way street works fine, though. To get around this (as I am usually trying to pave over the road with a one-way road while leaving the street intact) I either pave road over the streets at the intersection, just one square in every direction, or I bulldoze that intersection altogether (using zone view to not bulldoze all my buildings due to my shaky mouse ...) and rebuild after placing the one-way road, as SC4BOY suggested.

As for changing a one-way road to a regular road, I suspect that similar issues arise.  It tends to be remedied by avoiding streets at the intersection itself.