I've set myself some goals related to my bike ride to work. One of those was to do the ride in a net average speed (including stops) of 20 mph. Ten years ago when I was making a similar ride to Chelmsford my record time for the summer worked out to just about exactly 20 mph; I'm older now, but the ride's only three-quarters as long so it makes a good goal.
A lot of making good time is handling the hills. The most important thing is to build up speed quickly at the top of the hill instead of taking the opportunity to rest; that makes a huge difference to your average speed and you can rest once you're actually up to speed on the downslope. But the real key on this ride is that none of the hills are very high, so it's possible to sprint over them. I've been sprinting over bigger and bigger hills, and today I sprinted over Clarendon Hill, which at 55 feet elevation gain is the highest hill on my ride home.
Today's time works out to 19.7 mph. One more minute off my time and I'll be there.