Pro Pilot I believe is "level 2" autonomy so it can only drive on the freeway, single lane travel and for very short periods of time only.
You need to have your hands on the wheel but you don't have to provide steering control. During my test drive, if I took my hands off the wheel in about 3 seconds the car starts a series of warnings and alerts that will eventually bring the car to a stop in its lane and turn on emergency flashers. So no taking naps but if you need a 5-10 second break, the LEAF does very well for that.
Pro Pilot is scheduled for upgrades in 2020 and 2022 which you may be able to get on the 2018 for a price. I have no info on that (nor does anyone at Nissan yet when asked if hardware upgrades would be required but realize I pretty much only had access to media people)
I will say the car tracked VERY well even on fairly sharp curves at freeway speed. I have been in other "somewhat" autonomous cars and they tended to wander quite a bit in their lane. The LEAF was dead center steady the whole time.
Now all this comes from a 20 min stint behind the wheel on a predetermined course so no real idea how it would work in the wild but will say the freeways we were on only had rumple strips for lane markers.
2011 SL; 44,598 miles. 2013 S; 44,840 miles.2016 S30 (build 10/2016)"low water marks" 24,261.3 miles.363 GIDAhr 80.66Hx95.95%kwh28.1QCs205,L2's 226
My Blog; http://daveinolywa.blogspot.com
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