This assumes the same number of people will use them, just more slowly. But this is quite obviously false if you think it through. If the highway is so backed up you can’t get onto it then you won’t use it, will you? I would be fairly confident that this more than offsets the idling engines. Covid was a big eye opener in realizing how much traffic actually protects us from the real dangers of unfettered high speed traffic.

This individual protest may only have a small effect but it seems we’re seeing more of these as time goes on, and the more often they happen, the bigger the impact.