Human drivers also operate the turn signals on the vehicles.

Context: this was said in August 2019, about vehicles described in Brooks's post (likely semi-autonomous or self-driving test vehicles, or cars with driver-assist systems). True if the evidence shows that on those vehicles, at that time, the human driver or safety driver had to operate the turn signals themselves rather than the automated system doing it. Mostly true if this was generally the case with minor exceptions (e.g. some models or modes signalled automatically). Mixed if it varied substantially across the vehicles discussed. Mostly false if the automated system usually operated the signals and humans did so only in limited cases. False if the vehicles' automation operated the turn signals.

Set before the research began.

1. E1 ‘Self-driving’ vehicles may need human help for a while yet - The Boston Globe The Boston Globe · 18 August 2019

   “On my ride, the first thing I noticed was that the driver was triggering the turn signals. I got two answers when I asked about that: that turn signals hadn’t been woven into the company’s system, and that it helped the driver stay alert if he was responsible for a task.”

2. E2 ‘Self-driving’ vehicles may need human help for a while yet - The Boston Globe The Boston Globe · 18 August 2019

   “Optimus Ride is one of a few Boston companies that are developing technologies for driverless, or autonomous, vehicles. (The company doesn’t actually build them; they are made by Polaris, the Canadian maker of snowmobiles and all-terrain vehicles. Optimus outfits each one with cameras and sensors.)”

3. E3 Tesla introduces no-confirmation Navigate on Autopilot Teslarati · 3 April 2019

   “With the system in place, drivers could have their vehicles perform lane changes on their own without confirming the maneuver through the vehicle’s turn signal stalk.”

4. E4 No more turn-signal affirmation for Tesla Navigate on Autopilot Green Car Reports · 5 April 2019

   “Until now, though, the cars couldn't change lanes without driver approval. When they encountered slower traffic, or even need to change lanes to take an off-ramp, the car would alert the driver of the need to change lanes, and the driver would have to approve the lane change by activating the turn signal.”

The claim checks out. A Boston Globe report from 18 August 2019 (E1, E2) describes a ride in an Optimus Ride vehicle and says the safety driver was working the turn signals. The reporter was given two answers: turn signals had not been built into the company's system, and the task helped keep the driver alert [E1]. This matches the claim, made two days later, that the humans operate the turn signals. The Tesla items (E3, E4) are about a different system's lane-change confirmations, not the vehicles in the claim, so they don't change the verdict.