Gig economy

I may have found a mistake, the gig economy situation raises car usage, but decreases motorist membership. Was it supposed to raise motorist membership?

I don’t think so.
Gig economy is particularly relevant to Uber-drivers and jobs like that. More people use Uber drivers (when they might otherwise have used public transport). More people get cars to be Uber drivers, or the ones who already have cars use them significantly more, because they drive around their customers.