Walk or Bike
These obvious choices are (by far) the best way reduce pollution as they produce no emissions. Many cities are experimenting with bike share programs similar to car cooperatives. While something of a challenge for a regular driver, most experts suggest not replacing a car with a bike in most cases, but rather parking the car and using a bike or walking to do errands. Most errands within about a mile (1.6 kilometers) are comfortable by foot, and anything up to 5 miles (8.1 kilometers) is doable by bike. And, in addition to polluting less, the person gets the benefit of exercise.
Making the switch isn't easy. Many streets and cities are not particularly bike- or pedestrian-friendly. Experts suggest starting small and easing into an alternate car routine. In essence, they suggest you have some experience before biking or walking in traffic.
There are several Internet sites with tips, tricks and links to maps and mapping software for pedestrians and bicyclists to avoid the worst of the pitfalls.
If a person can't bike because of bad knees or other health issues, companies now produce electric motor kits that significantly reduce the physical power needed to ride a bike.