Detouring back to the ACC conversation from last week:
I almost always drive with ACC on and always monitor the instrument panel when driving. When ACC detects a vehicle ahead, a red car icon is displayed in the top center of the instrument panel. If we are approaching a vehicle ahead and the red icon does not appear when I know that it should, I disconnect ACC and take over driving. This has happened twice since we purchased our i3 in 2014, so it's no big deal.
I'm a light user of ACC since 2014 and wanted to share my first non-detection experience from last week.
Like others have said, ACC is primitive. The tech was probably validated back in 2012 or 2013 for production so it's been around a good while. I use it as an assist as I've had more than a few random disconnects in the past.
Last week I had ACC on, set for 72 with a three-brick following distance. Traffic was moving well as it was a few hours before the rush hour. Ahead of me, beyond the system's range, was a cab truck with a long flatbed, no side rails – the kind your lumber yard would use to deliver a load of drywall. It had taillights, but they weren't on and the truck was dirty (low-contrast).
It was fascinating to watch ACC fail to acquire the truck at the expected distance. Our closing speed was not more than 2-3 mph and I let the system go until there was about a car length left between us – still no "red car" icon. ACC would have happily driven me right up into the back of the truck had I not disengaged.
I give the system a short leash, but this is the first time I've seen it be completely oblivious to a vehicle.