I drove a dedicated route that had me back home every 4-5 days. This was back during the Clinton era.
Union drivers comprise more of the industry than you realize. Kroger Inc., for example, is a closed shop; you want to work, you’re union. UPS ground transport, same thing. Organized trucking services the urban areas, the places most affected during a shutdown.
I don’t doubt there are unionized truckers. You were lucky by the way to have one of those dedicated routes. Sure beats sitting at a terminal waiting or a truck stop waiting days for a load. Just the same, I would say that the percentage of union long haul drivers is very low. But, why guess when we can know. Shall we look it up. We are both speaking from anecdotal information.
By the way, thanks for the job you did. I will always have an appreciation for truckers ever since the day our family got in distress along a highway and it was only a trucker that stopped to help.