There's a lot of externalizing of costs going on. The trucks are idling because the drivers are operating at the slimmest possible margin under the assumption that idling doesn't cost anything.

What we actually would want to get to is that idling does have a cost (environmental, health, pleasantness of the area, etc). And that cost ought to be passed up the chain so that the various goods being shipped are more expensive.

But without a more centrally-managed economy, the implementation is to put all the pressure on the truck drivers and leave them responsible for passing that pressure to the next step up the chain. It doesn't work out very well in practice because the drivers need to make a bunch of capital expenses for something like adding a cab AC and adding a batter-powered lift, but they've been operating at low margins so they're not in a position to do it.