My wife and I ran the local Drumstick Dash 10k on Thanksgiving day, it was 2 loops around Lake Harriet and happens to be the first "road race" that I have run in over in a year. It was so weird to be at a road race versus a trail race or an ultra. There were so many people, probably like 500 (actually I just checked and there were 852 finishers, no wonder it seemed so crowed, it was).
Anyway, this is not a race report although I should say my wife and I ran a nice consistent pace and finished with a negative split. This is a report on spitting, I have often wondered how many times I spit during a run, for this run, I counted. When I took my last spit, I was on count 61, so that pretty much averages to spitting 10 times/mile, 1 time/minute, I am not sure this is normal but it does seem to be what I do. I do know that I had to consider my surroundings (said differently my fellow runners) for each and every spit and I can safely say that to my knowledge no other runners were negatively affected.
My guess is it might be allergy related or it might just be a learned behavior, the one thing I know is that it is a whole lot easier to do on the trails, yet another reason to stay off the roads.