One of the current trends in hybrids and fuel efficient cars are stop/start engines. These are engines that stop automatically when you idle for more than a few seconds, then restart when you step on the accelerator. VW pioneered this in the 1990s with one of their Golf models - I can't remember the name - Ecomotion maybe? The problem at the time was the additional stress on the engine and starter motor resulted in much less longevity for those components. Starters failed after 15,000 miles, engines had excessive wear and various other issues cropped up, all related to the constant stopping and starting of the engine. I'm left wondering if it's really worth it. Are the newer generation stop/start systems that much better? What about all the additional complexity that is required? For example when you stop the engine, you can't stop everything else - heated windows, radios, electric components - windscreen wipers and headlights etc. So you need a hugely uprated electrical system and battery (or batteries). Then there's the heater / air conditioner which run off the coolant fluid or a/c compressor respectively. To compensate for stop/start, you'd need electric a/c and electric heating too. Can all the added weight and complexity really be good for the consumer? Is it reliable?
In Hybrids, it's not an issue - they've been designed from the start to have all these systems running on electric-only if the engine is off. But on non hybrid vehicles it does seem like a lot of complexity for not very much return.