. >> reporter: maureen fitzgerald, a trucker's trucker with 30 yars' experience. she was our safety driver, baby-sitting with no intention of gripping the wheel, but there just in case. riding shotgun an engineer, john pantella, there to monitor the software. the driverless truck was attempting a 65 mile loop in weekday traffic through tucson. the map was routed and mapped in before the run, but that's about it. the rest was up to the computer, which makes 20 decisions per second about what to do on the road. as we rolled past distracted drivers, disabled cars, slowpokes and sheriffs, our safety driver kept vigil but never disengaged the driverless system. >> watching the front targets close in. yep, got to cut in right now. 55 miles per hour bad cutoff. this guy just flagrantly cut us off. >> he really cut us off. we did not honk at him. did we disengage? >> we did not disengage. this vehicle will detect that kind of behavior faster than the humans. >> reporter: how far away are we able to pick up the faster cars passing us? >> that's joe from new jersey. we can

. >> maureen fitzgerald: is everybody buckled in?led in. >> fitzgerald: three, two, one. ...and we hit go. >> truck computer: autonomous driving started. driving started. >> wertheim: we sat in the back alongside the computer. in the front seat: maureen fitzgerald, a trucker's trucker with 30 years experience. she was our safety driver, babysitting with no intention of gripping the wheel, but there just in case. riding shot-gun: an engineer, john panttila-- there to monitor the software. the driverless truck was attempting a 65-mile loop in weekday traffic through tucson. the route was mapped and programmed in before the run, but that's about it. the rest was up to the computer, which makes 20 decisions per second about what to do on the road. as we rolled past distracted drivers, disabled cars, slowpokes and sheriffs, our safety driver kept vigil, but never disengaged the driverless system. >> john panttila: watching the front targets close in a hundred. yep. got to cut in right now. 55 mile an hour. bad cut-off. >> wertheim: this g