Mild hybrids.
These are essentially conventional fossil-fuel vehicles equipped
with a large electric machine (one motor/generator in a parallel
configuration) allowing the engine to be turned off whenever the
car is coasting, braking, or stopped, yet restart quickly. Mild hybrids
may employ regenerative braking and some level of power assist to
the ICE, but mild hybrids do not have an exclusive electric-only mode
of propulsion. A start-stop system or stop-start system automatically
shuts down and restarts the internal combustion engine to reduce
the amount of time the engine spends idling, thereby improving fuel
economy and reducing emissions.