I don't think it matters really - even the slightest breeze will disperse/dilute any virus to pretty much zero in no time. I was out the other day and a truck ahead of me blasted a big gout of black exhaust - don't know if it was a mis-timed "coal roll" or if he was downshifting to climb a hill and his rings were bad - in any case, even though this is only maybe 50 yds ahead of me, it had been completely dispersed by the time I got there. I understand that smoke isn't virus, but it illustrates the dispersal power of the great outdoors. I personally have no concerns driving with the roof down these days. Same with cycling - I ride on country roads avoid crowds, give riders a decently wide berth if I overtake - out on the bike is probably the safest place I can be, COVIDly speaking