Originally Posted by hoadie72
Let's put this in perspective. A typical family might start and stop their car engine 20 times over a weekend and god knows how many times during the week. That starter motor will last 20+ years. So starting and stopping it during a few times during a commute isn't going to make a lot of difference.
The average trip length for urban vehicles is something like 10km/6miles; the average traffic light interval is probably more like 0.5km/0.3miles. Restarting at every second traffic light instead of just once per trip has the potential to reduce the life of starter motors and ring gears by a factor of ten, bringing your hypothetical 20 year starter life back to just 2 years.
Automated engine off and restart at stops in traffic lights has only become viable with larger batteries and starters.