How many seconds do you need to cross a four lane street?

I never run. They'll wait.

If it's flashing 0, or if the cars are still stopped, I will go. Not all crosswalks have the same lighting system tho.

I meander. It takes a few seconds.

Less than 1! I nah-root-oh run, or whatever the kids are saying these days

Longer than a walk signal gives you. They are meant to allow so much then cut off so the remaining traffic can get cleared before the cross traffic light goes green. If anyone ever pays attention anymore, when the walk sign starts flashing in the states the majority of them flash 13 times then the green goes yellow then red.

I don't know, I not much of a pedestrian.

You would go faster if theres less time avalible. Fasted you could make it if your in decent shape is maybe 8 seconds. Do 10 to give yourself a buffer prolly.

If the light on the other side is still red I continue. If I'm half way across and the opposing street turns yellow I speed walk across since that gives me 3 seconds to cross.

I don't know. I haven't really timed myself.