As mentioned above I was flirting with 20mph average speeds on a 25 mile two-way commute (most trips were ~40min saddle time, some ~35min.).
cyclist5 you are a high performance commuter in my book.

Actually, I think I'm somewhat unique in that I include all the time. It's not like the waiting at lights magically doesn't make me later for work. I'm thinking of changing it up, though, because I'm curious how much of my variance in elapsed time is due to me, and how much to the lights.

Just skipping time spent at lights isn't enough to compensate for them since you're also spending significant time decelerating for them and accelerating from a stop.

For example on one morning commute I took 47:38 of wall clock time to cover my 11.8 miles of which only 6.6 minutes were at zero speed although 10.9 minutes were at zero cadence and 12 minutes were at zero power (I spin the cranks a little to down shift approaching lights).

Looking at the ride plot one acceleration from 0-20 MPH takes about 18 seconds which wouldn't be bad; although the route includes 10 stop signs and 24 traffic lights of which only one is a right turn where I can proceed when the light is red. That ride seems to include 17 stops which would be 306 seconds accelerating or another 5 minutes that aren't at full speed.

Then there are indirect effects - stopping lets you recover and go harder when you restart; but stress is roughly proportional to the square of power so accelerating at 2-3X your one hour power is 4-9X as hard as just cruising along for the same time period.

Yeah, for me, traffic lights, and one stop sign at a busy street were a significant source of variation. Probably the worst case was +4min on my usual route, as there was only one each potentially long light & stop sign. Only other significant source of variation was wind. Just the same, the elapsed times I logged for my own reference and posted in this thread were from setting out at the beginning to dismounting at the end of my trip.

Why thanks! I just love riding fast I had to invest some cash to get faster though.

this is sooooooooooooooooooo true. my usual commute takes an hour, about 53m of moving and 7m of waiting at various intersections. then last Saturday I took off early when there was no traffic and didn't have to stop the entire 13 miles. made it in 45:30.

I have found that if I make loads more effort I get an extra mph or 2 and only cut 2 minutes off my time. So I might as well take it a bit easier and relax more!

Even so since riding fixed gear all winter, I can now easily average 20mph+ on some sections of my commute - which is fun

Agreed, increased effort yields diminishing returns. I put out the effort that I'm comfortable with (commuting being part of my exercise regimen); that resulted in my ~20mph average speed on my previous commute. My new (yet untried) commute will be ~25 miles 1-way; thankfully little elevation change, but probably some waiting at lights in the city end of it.

Cyclist5, IMO the cheapest ways to go faster are, in order of importance (Assuming you have a decent road/touring bike to begin with):

• get in better shape
• ride on the drops as much as possible & lower them as much as you comfortably can
• minimize weight & bulk of items carried along with you on commute
• optimize tires & pressure for your route
• evaluate your gearing and if necessary, re-configure the ratios to optimize them for your route & riding style

After the above, getting faster by upgrading equipment will get real expensive.

Well I found getting fitter came after getting better equipment. And by equipment I meant a road bike, kevlar slicks, and cycling clothes. I'd say it went from 10mph top to 22mph average. That and going from 40lbs to 20lbs of books and emergency gear