That's so weird: nobody uses miles in Italy (or Europe, except the UK). I checked the article and the source is Strava Insight which probably defaults to miles. The journalist copied and pasted without converting the units into something readers would understand.

14.8 miles per hour is 23,68. I usually do 20 when I move in the city because I don't want to sweat and I don't see many bikers going faster than me. Maybe that's because only fast bikers use Strava and it skews distances and speeds.

I would never log my daily 3km ride to work in Strava, and I've had it count my after work singletrack romps as commutes. How strava thinks it can be a good source of commuter data is beyond me.

Averages are pretty useless without standard deviation.

The average speed is kinda fast but not insane, especially if most of the ride is on a stretch without many intersections (which you'd expect to be true of a 9 mile ride). I average around 15 mph in a mostly flat area where I stop every few blocks. TBF I'm probably riding a bit more aggressively than a typical Milanese bike commuter.

I wouldn't be at all surprised if the average American bike commuter averages 15 mph. But I'd also expect the average American bike commuter to be much faster than the average Milanese bike commuter because in the USA most bike commuters are dedicated enthusiasts.

18.7 miles per day seems like a really high average, but is entirely believable. I used to do something close to that, and our summers were also hot.

I can add something about Milan that could explain those data. Milan has some water channels going at least halfway into the city. Some bicycle roads follow the channels and they don't have many intersections. Some 10 miles each way are believable. People doing 10+10 miles each day on those roads could be the kind of people that also record their commutes with Strava. However people that have to commute on normal roads shared with cars probably can't be that fast.

I live inside the city and I never mount my bike computer when moving around in there. The normal cyclists that use a bicycle to go shopping probably don't do more than 12 km/h, twice as much as a fast pedestrian. Obviously they don't record their journeys.

So, still skewed data but with an explanation.

The "miles per day" would suggest 9.35miles each way, so ~40 minutes each way, which seems more likely.