Out in the countryside - without time-killing (and door-to-door ET) average stoplights, you can get away with this... Imagine being stopped at just ONE stoplight for over a minute.

My work commute is 12.5 miles - with 10 straight-through stoplights (not counting my commute's two right-turn-on-reds-after-stop) My commute times are somewhere between 42 and 45 minutes, thanks to time spent waiting at those lights. I have NEVER - in seven years - been lucky enough to hit it where all of the lights are green... ...and no, I do not blow through ANY traffic lights! 42 minutes is 17.86mph AVERAGE door-to-door speed. 45 minutes would be 16.67mph door-to-door speed. 41min=18.3mph 40min=18.75mph 39.5min would be your target 19mph (actually 18.987mph)...

Still, I think that I'm doing OK for an asthmatic 63-yr-old near-Clyde, riding a 24+ pound steel-frame 35+ yr old bike!