VCSL2015

Holy S batman. According to this info on SE im more out of shape than i thought

Speed varies widely by cyclist, depending on fitness, road conditions and traffic. Some of my observations (cruising speed based on a flat, paved road in good condition):

20km/h - many "occasional" cyclists ride around this speed
25km/h - most commuters
30km/h - fast commuters, slower roadies
35km/h - fast roadies
any faster than that on a long flat and they're probably a racer
(based on who I pass and who passes me when riding around 30km/h)

Average speed will usually be slower than you think, once traffic stops and hills are factored in, especially over longer distances (like 80km). On my 21km commute I'll hit 30+ on every long stretch I can, but my average still only works out to 24km/h. For longer rides I cruise around 27-28 km/h, which is more sustainable; averaging 22-24 over a very long ride (200km) is a great pace for me.

SpikedLemon

Consider the caveat that they talk about cruising on flat roads. Maintaining a decent pace on a flat, paved, road is vastly different than rolling hills or gravel paths.

I don't have an app or speedometer on my bike (I check the distance on google maps afterwards & note my total time) but the speeds sound reasonable to me for flat, paved, ground with no stop signs/traffic lights.

DMC707

Even among paved road surfaces, - some types of blacktop really seem to suck more power out of my legs than others --- i have a nice loop i use frequently , but it feels like i am pedalling through sand sometimes due to the road condition --- other places around town i can average 2 mph more

pdlamb

Traffic lights, stop signs, and hills can really suck the speed out of a commute. 15 mph (aka 25 kph) is fairly easy for me on a straight, flat road. Until I have to stop for traffic control devices and climb over that last hill on the way to work. Then I'm lucky to have averaged 14, and more often 13.5 mph. (22-23 kph for advanced societies.)

nkfrench 

I'm 2-3mph slower on city streets than on routes with few stopsigns. It's all about the loss of momentum.
Are the averages you cite calculated off elapsed time for the distance, or just the moving time for the distance.

Paved roads. There's normal pavement. There's rough/chipsealed/damaged pavement that you can't keep momentum on.
And I've been on quirky pavement on frontage road ramps that is very easy to climb on. Smooth concrete with tiny crosswise grooves.

IBOHUNT

There are a tonne of factors that play into average speed as some have noted. Poor @TrojanHorse has stop signs planted in the road just because they decided to put one in. The bike and wheels play a role in it as well.

If you want speed it takes work. It's fairly easy to get the average from 22 - 30 kph but getting above that the gains come all to slow.

My best solo 206K (got lost for 6K) was a very FLAT ride at about 10'/mi which I did at 80% effort and I can only average that speed here at home on my 35 mile (56k) training loop which is an average of 55'/mi and it's an all out effort.