You’re undermining the point you’re trying to make, @SpatzieLover. If the area to be covered was, say, a relatively flat field or meadow as it was turned into a parking lot, then your calculation of runoff would be a very high percentage of what could have and probably would have soaked into the ground. (In the exceptional storm events that @Imadethisupwithnoforethought was talking about, even the field would have eventually reached a point of saturation or inundation, at which point all of the added water would turn to runoff, too.)
But if you’re talking about paving a gravel or dirt road on a steep hill, then most of that water is already runoff. (In fact, it includes a lot of eroded material from the hill, too.) So there may, in fact, be a net reduction in total runoff, since there should be less mud and gravel from the roadway washing down.
In addition to the foregoing, a roadway improvement such as paving should definitely include some kind of method to handle runoff, either by periodically shunting it to standing pools at the side of the road where it can eventually seep into the soil, or by installing catch basins and drainage piping, or even drainage ditches and culverts to channel that water to a common point. Otherwise even the asphalt paving will eventually be eroded.