Retrofitting automobiles has always been a cost effective way to modify your vehicle. This new firm (very well funded, however!) plans to make add-on self-driving kits for Class 8 trucks. I think this is a very realistic thing to do, since semis have very long lifetimes in service.
Former employees of Google, Apple, Tesla, Cruise Automation, and others – 40 people in total – have formed a new San Francisco-based company called Otto with the goal of turning commercial trucks into self-driving freight haulers.
Source: Turning Truckers into Self-Driving Freight Haulers – Supply Chain 24/7
We have plenty of evidence of long truck lifetimes from the Clean Trucks program at the Ports of Los Angeles/ Long Beach. Emissions retrofit kits were required since so many drayage truckers were driving vehicles earlier than 2007, and had no means of affording a later model one with a less polluting engine. Failure to understand this gave rise to a prolonged dispute between the San Pedro Bay ports and truckers, leading to a Supreme Court case. The fight was not over pollution control; everyone wanted that. It was about whether the ports could compel drivers to be employees of large firms who would be more likely to afford the newer trucks. Most drayage drivers in the US are independent owner-operators who own their own truck; they work on piece rates and are usually cheaper than the mostly unionized larger drayage firms.
It is a classic example of unintended consequences of regulations and attempts to comply with them. It wasn’t the CARB (California Air Resources Board) rule on pollution that was the culprit. It was the details of the port’s reaction.
Some other posts from the same source about self-driving vehicles (the first has a report download):
The question is no longer “if” but rather “when” autonomous vehicles will appear on our streets and highways and DHL is ready to take a front seat on this journey.
Source: Self-Driving Vehicles in Logistics – Supply Chain 24/7 Paper
The Nikola Motor Company has emerged from a state of being unknown to unveiling plans for the first-ever 2000 horsepower (HP) electric class 8 semi-truck, called the Nikola One (named after Nikola Tesla).
Source: Nikola Motor Company Wants To Be the Tesla of the ‘Big Rig’ Trucking Industry – Supply Chain 24/7
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Here’s a white paper from California State University Long Beach which was used in the deliberations. 
Freight Efficiency White Papers_Final Version
Supply Chain and Logistics 