Given the type of bike, I think the most practical way to get through an intersection quickly will be:
- start in quite a low gear, something you'd climb hills in
- push off, stand on the pedals for a few strokes to get off the line
- then sit and quickly spin the revs up to pretty high, like 100 rpm or so
- quickly change up one gear, revs up, change up, revs, etc.
Basic idea is using leg speed, high rpm and lower gear, instead of using leg power, low rpm, and higher gear. Like accelerating a manual shift car, you start in a low gear, keep the motor at a high rpm, and flick through the gears. OP will probably be through the intersection by the second gear change.
Reason? This is a city-type bike with upright position, high and swept back bars, platform pedals, step through frame. It isn't designed for the rider to apply big power like on a sprint. You can't get the right body position, pull down hard on the bars, or push and pull hard on the pedals. I also think the OP is a nicely dressed lady in skirts and street shoes, not in tights and cleated bike shoes. Finally, I think the OP should be able to get across the intersection quickly now, without first spending months in the weight room building thighs like steel thunder. So track start technique might be of limited relevance and a fixed gear bike would be a bad choice.
Practicing fast gear changing will be helpful. I can't recall if the bike has IGH or derailleur, but anyway it has indexed shifting so you can bang through the shifts quickly.
Good advice. Thanks. My current bike is a hybrid with flat bars and derailleur gearing. New bike is steel step-through with swept back bars and IGH (class dutch bike, but a little lighter). I think you are right that these techniques are probably going to work best. I'm still going to try the interval training though. I put a lot of miles on, so even though I'm riding in a dress and street shoes, my legs are pretty strong and surprisingly muscular. I might be able to add a little power to the mix, especially on one particularly busy and wide road crossing that I have in mind.