> fewer people traveling
I don't think anyone says to themselves "it's a 20mph zone on the route so I'm not going, if it was 30 I would go." Lower speed limit != fewer travelers.
> less air population
Assuming you meant pollution, the same amount of cars going slower would cause more pollution in a given area, not less.
> people having more time to meditate
I'm sorry what? Most people don't meditate, and how is sitting in the car longer going to give you more time to meditate?
Longer travel times result in fewer people wanting to travel. Was not expecting this to be controversial.
> The same amount of cars going slower would cause more pollution in a given area
Drag is proportional to the square of the velocity
> Most people don't meditate, and how is sitting in the car longer going to give you more time to meditate?
Meditate is perhaps the wrong word.
In general the slower you drive the lower your mpg (and hence pollution).
But even that does not take into account secondary effects to reducing the speed limit like fewer people traveling, less air population, people having more time to meditate, etc... All in all, it's very hard to estimate the impact of such policy.