What fraction of the economy do they make up?
What if efficiency gains are not 2x, but 10x? What if you'll only need to employ one trucker to do the job of 10? Do you think demand for trucking will go up 10x? This isn't a web framework.
Trucking costs are built into most products. My grocery store sells apples from California. If the cost of trucking them to me goes down, those apples will decrease in cost and they will potentially sell more apples.
Automation of driving is all about making people with lots of capital richer. Efficiency is just the dream -- this stuff will dramatically increase costs of shipping as capacity is constrained.
For example, I just requested quotes for waterjetting some stuff today. If LTL shipping were cheap enough to I'd look outside the high CoL sphincter of the country where I happen to reside but instead I'm stuck paying a premium because the local cost of everything is high. There's also a cylinder head in my garage for a 60s Ford I'd like to give to someone who needs it but nobody needs it bad enough to pay for me to ship it across the country.
At the higher volume levels similar stuff happens. A construction company may source steel from farther away to undercut it's competition. You can bet the logistics people at Walmart (and anyone else with a big fleet) are drooling over all the optimizations they could implement if trucks could run like call centers.
This is the only point I seek to make.
If salaries are 60% of the cost of shipping, and self-driving trucks make drivers twice as productive, costs will drop 30%.
This will bring a demand increase of less then 30%. Let's say 15%.
... Doing the math, it looks like 42% of truckers just lost their jobs. But at least they can buy more apples with the money they no longer have.
The bigger the productivity gain, the worse it will look for them.
Lots of products have price elasticity of greater than 1.
Shipping seems like a very elastic industry. If anything, demand would increase by more than 1% for every 1% decrease in cost.
This is because shipping costs if shipping costs are low enough, then you can build something for cheap somewhere else and then ship stuff across the country to high cost of living locations.
YOU wouldn't ship stuff more, but industry would.
IE imagine if something costs 1/3 if it is made in China.
If shipping costs are more then you save, then nobody would ship it. But if shipping costs go down, now you can easy get those cost benefits of across world or across country manufacturing.