Alex,
In my experience, paving the road to get the crown is the most effective approach. Some folks build their roads out of sheet styrene with a strip along the center underneath. That sounds great for straight sections, but I don't see how it would work well for curves without some serious design help (i.e. engineering plans). Others use AMI instant roadbed or cork roadbed with good success, too. But what I've done in the past is basically mimic the real world process.
I cut the road profile out of plastic, usually something somewhat thick, like 0.040" or thicker sheet, to make a giant screed. I extend the profile out an inch or so past the back of curb if there's not going to be any sidewalks or an inch past the back of the sidewalks. Next, draw out exactly where the road goes on the layout and cut strip styrene or balsa wood to fit the limits of the roadway. I place these stripwood or styrene form boards on either side of the roadway to be paved making sure they're at least twice the height difference between the bottom of the gutter and the top of the curb. I mix up some Sculptamold and pour it in the forms letting it get somwhat set up, but not too much. Then I drag the screed along the paved roadway, cleaning it with a damp rag after each pass. I keep the road moist with a spray bottle, which prevents the screed from pulling chunks out of the roadway or making drag marks.
I've never mixed in color with Sculptamold, but I think I'll try it out next time. My Fort Worth modules require massive amounts of paving, so I'm sure I'll get lots of practice. Also, the current design for my modules calls for roads paved in several different eras, so I'll be learning how to do brick streets, asphalt with concrete curb and gutter, as well as the modern monolithic curb, gutter and roadway sections.
As with anything else, study the prototype to see what you can observe yourself. Your own observations are your best tools for doing any modeling job because they are the ones you remember.