[ljf]

I'm not too sure about your ability to gauge others speeds.

Most cyclists (or at least the average cyclist) is not doing 20mp+.

I cycled daily for nearly 10 years, and while I could sprint fast, 20mph was my standard speed, and I was faster than the majority of the East London to West London cycle traffic (and more traffic tbh) - for a good period had the Strava KoH to prove it. Those that beat me were usually coming out at night to complete set sections of the route so as not to compete with traffic.

I'm not as fit as I was, and on the flat 20mph is now my 'good speed' - I can hit 25 when going for it, and even 30 if I can draft in behind a better cyclist or a van. Was the junction at Bank on a steep downhill section for the person to do 40mph?

How are you so sure people are riding at 20 on the pavement? I would be terrified to do 20 on a London pavement - such a thin area to cycle on, and risk of doors opening, and traffic etc.