My average is worked out over the whole distance of the ride. if you see my strava ride you'll see that my ride is listed as 8.8 (9.2 but strava takes off 2 tenths each end so for privacy, not relevent) and the time is 31.17.Right il post a picture of the strava app , note the diff between top speed ( which is what I'm sure folk are quoting their ave as ) and the actual average ( stopping at lights / getting going again/ gen road commuting£
This is my commute to work through Glasgow and as u can see I wasn't hanging about ( by no means fast but a few wee downhill sections )
It's one iv posted before but it illustrates what iv said
this website http://www.machinehead-software.co.uk/bike/speed_distance_time_calc.html works out the average as 16.877mph
My top speed on that ride was I think 27.7 mph but only for a couple of hundred yards.