Sailing on Autopilot on the Beltway, I knew the lane to my right was open. I checked over my shoulder, looked at mirrors, checked again, then flicked the blinker on my Tesla Model S P90D.

And then from out of nowhere came the white pickup truck.

Autopilot had no answer for this. I grabbed the wheel and swerved left: Collision averted. In the name of journalism, I did not wreck a $132,700 car.

During my drive, I was hooked up to a system called “BrainWave,” software from the Bethesda-based human factors firm Spark Experience. The system measures attentiveness, emotion and emotional intensity. In May, I’d watched Spark hook voters up to the same system and try to guess for whom they would vote.

Now, Spark wanted to try the system on drivers to collect data on how people feel about semiautonomous and rapidly accelerating cars. Spark chief executive Spencer Gerrol and neuroscientist Ryan McGarry drafted me as one of their test subjects.

I’d drive a Honda Civic around Bethesda that McGarry would use to measure my baseline driving emotions.

Then I’d try the Tesla. All the while, McGarry rode shotgun tracking the data that poured out of my brain.

BrainWave eliminates biases created by focus groups or questionnaires for similar studies. Instead, experimenters harvest data directly from the brain without external interference.

That way it gets a clear reading of how the human brain feels about letting go of the steering wheel in heavy traffic, or going from zero to 60 mph in 2.8 seconds.

Attention, measured through an algorithm that collects data from the BrainWave gear, is scored on a zero to 10 scale in which zero is no attention at all and 10 is fascination. Emotion, measured through a similar algorithm, is scored on a -10 to 10 scale, where -10 is complete loathing and 10 is absolute joy.

When the Honda Civic lethargically accelerated down Old Georgetown Road, my emotional scores dropped. I was frustrated. The car didn’t zip, not even like my Toyota Camry.

I didn’t actively dislike the Honda, I told Gerrol and McGarry. But emotion is subconscious. Yes, I said one thing, but my emotions said something else.

My attention waned immediately in the Civic. I scored at about 4, or as much attention the average person pays a boring commercial. I had my eyes on the road. I checked my mirrors, the speedometer and looked over my shoulder when I changed lanes. I drove safely. But my mind was elsewhere, BrainWave detected, probably on my passengers or thinking about this story.

You actually don’t need to be that attentive to drive safely, Gerrol said, in the same way you don’t need to pay much attention when brushing your teeth. The activity is so routine, it leaves vast regions of our brains available to do other things.

That wasn’t the case when I got into the Tesla.

For one, the cockpit doesn’t look like one you’d find in a regular car. The entire middle console is a giant display screen. So is the dashboard. To put the car in drive, you engage a shaft that looks like it should control windshield wipers.

And yet I didn’t always pay more attention while driving the Tesla. I was still hovering at around 4 when driving the car normally.

The times my attention peaked, it wasn’t always positive. My emotion scores dipped to -5.5 when I couldn’t figure out how to put the car in park or turn off the radio. Drivers for generations have trained themselves to use specifically placed features in almost every car. Think about the gear shift or parking brake. When those features deviate from their standard position, that’s annoying.

Its “ludicrous speed mode,” which goes from zero to 60 mph in 2.8 seconds, is fun. There’s no delay in acceleration: Your foot hits the gas and the car takes off. The engine is silent, so there’s no revving up as the car zooms ahead. As such, it’s sometimes hard to tell how fast you’re going. It’s scary, but great-big-roller coaster scary.

The Tesla kept my attention scores high while using the new features. I paid more attention to the road — a full 8 out of 10 — after I activated Autopilot. While self-parking, I freaked out as we neared, then pulled away from, then neared again curbs and other cars and shrubs. My attention score jumped back up to nearly 10 of 10. 

“When it comes to Autopilot in particular, you’re the kind of person who is skeptical of technology but you’ll give it a chance to prove itself to you,” Gerrol told me days later after reviewing my data. “And if it does prove itself to you, you’ll want to trust it and you’ll like it.”

I was feeling good, I thought, like I could leave my Camry at Spark’s office a bit longer. And then that white pickup truck refused to let me change lanes, barreling down the exit lane like I don’t know what.

I snatched the wheel, tapped the accelerator swerved out of the way. And then I wanted my Camry back.