It sounds like you're working with a base assumption that increasing usage of cars is bad.
My base assumption is that moving people around is good. Freedom of movement and time-efficient movement. The car reigns supreme over trains, planes, and buses in those terms.
> the net impact was a slight time savings for suburban commuters for about six months, after which traffic was worse than before because more people were driving.
By the sound of it, more people were able to get where they were going because of the the Big Dig.
> Getting those people onto trains would be far more effective and cheaper
A breakdown of the numbers here would be great, but I'm not sure how much more time either of us want to spend lol. I like trains, but I'm cautious about them because they generally can't take people directly to an end destination the way an independent vehicle can. The US has also generally failed to use rail in a way that could replace cars in a meaningful way, despite rail having a decades-long head-start over the automobile.
> Similarly, delivery and garbage trucks aren’t affected at all by calming measures
I was under the (perhaps mistaken) impression that you wanted to remove or replace roads in cities to make way for alternative transportation. That's based on the statement in your original comment:
> Outside of freeways, we shouldn’t dedicate millions of dollars in public space to private car drivers,
I was not referring to traffic calming measures when I said that would be a logistical nightmare. I more meant that private cars share common infrastructure with a number of critical services; reducing their share of public space would harm those other services.