However, hybrid cars make very little sense. People that are now buying hybrids are paying about $11 a gallon for the gas they don't use!
When driving in the city or accelerating say for example to pass another vehicle the electric motor kicks in on a universal drive system to compensate. These driving conditions are where your biggest emission problems occur. Starting and stopping frequently and accelerating.
You only use the electrical motor for short distances in the city and when accelerating. The combustion engine,when used, runs at its peak operating point constantly - further improving efficiency. The key is targeting the biggest inefficiencies in operating conventional vehicles.