It's my understanding that road bikes are faster than folding bikes because they are lighter, geared for more top end speed, and allow the rider to take a more aerodynamic stance.
For those of you who've used both types of bikes, do those advantages actually make a difference in denser areas? (where I assume most of us live)
I could be wrong but it seems to me that those benefits mainly affect the top end. I personally can't see how it would matter with the amount of car crossings to worry about. I've never used an expensive road bike though