Hybrid electric vehicles can help reduce emissions and energy use in cars. Series hybrids control emissions better, while parallel hybrids can cut fuel consumption. Currently, parallel hybrids with small, powerful batteries are favored due to cost and marketing. New ultra high power batteries are being developed, which can improve energy efficiency and emissions. Regenerative braking and engine response smoothing can also help. Super capacitors can assist in achieving these goals. Challenges include managing battery life and finding energy-efficient strategies.