I doubt it would outperform EPA estimates (you can only recapture energy not create it afresh with regenerative braking), but compared to ICE cars the percentage of stated range would be very high.
It’s because air resistance is a much bigger drag on efficiency for an EV, so stop and go traffic is a bit more closer to its ideal efficiency (which is going slow without stopping).
The Chevy Volt PHEV had an estimated 53-mile all electric range. During the summer, I routinely got 56-60, and once got 67.5 miles before the engine had to kick in.
I used a Nissan Leaf as my thrice weekly commuter vehicle for several months. It couldn't quite make the full round trip on a 100% charge and there was nowhere to plugin at work. For a while, I'd go to Ikea at lunch and charge there during my lunch break. That was enough extra charge to make it all the way home but going to Ikea each day for lunch got old fast. Instead, I started stopping at charge point near a Fry's on the way home but even Fry's got boring after a few days. Then I discovered if I got off the freeway about fifteen miles earlier than my usual exit and used surface streets, I could make it home even though it was a bit longer distance and plenty of stop lights, stop signs, and traffic slower than the highway. I suspect the lower wind resistance at the slower speed is what provided the extra bit so I could get home with about nine miles of range showing on the dash. Probably wasn't good for the battery but it was the last few months of a lease and never ended up losing any bars of range. The anxiety sure was real.
My experience has been that the car does best when you’re driving at a steady speed of 25mph without having to stop. This is based on the internal chart that Tesla provides.
When you’re in stop and go, you actually use a lot more energy to go from 0->X but do not regenerate back enough when you come down to 0. On the other hand, maintaining a steady 25mph uses a lot less energy as compared to 0->X. Again, this is based on the Tesla energy usage data that they themselves show in car.
USA traffic engineers love stop lights which force idling. Fortunately some European tech to stop/start the engine is arriving in USA. In isolated cases, some USA intersections are being converted to traffic circles.
Installation of new stop lights should require a giant pollution fine paid by government.
It can be turned off, and there's very little visual indication that this has happened. The feature bugs some drivers, so if you have a second driver, they could have easily done it.
I've had this this issue on my Mercedes before, the cause turned out to be the 12V battery that never charged properly, so the system didn't want to activate.