IIRC the trend is observed over longer periods, where it feeds into people's decisions about whether to have a car or second car, and how far to commute. And even then, congestion and travel time are two different things - an extra lane probably makes no difference, but a new route or higher speed limit will get you there faster regardless.

Which this actually isn't a straight example of, exactly. Jevon's paradox says more and better roads will mean more cars operating, not less. That happens, but in this case the increase is so great, that it leads to the same level of congestion on the roads all over again.

The wiki uses the example of coal. Better boilers and engines increased the use of coal, but it's fair to say industrial Europe had better coal powered equipment afterwards, not the same or worse. (Although, to be fair, congestion is only one metric of traffic performance)

The number of car-hours per person per year isn't even close to fixed over the long run. The trend is basically that in the past, people might have carpooled, taken a bus or even hitchhiked, and usually lived close to their job. If the roads get better, they drive more.