One of the great things about comparative essays is that they can largely use any two topics to form the basis of the paper. Ultimately, with a comparative paper you are trying to outline any similarities and differences between the two topics and, therefore, the topics that you can write about can be as similar or different as can be. Nevertheless, it is often good to choose to topics that could be classed as coming from a similar general category, such as cars and walking, which can be associated with a category such as transport, or travel.
In fact, the topics of cars and walking provide a range of different possibilities when writing a comparative essay. For example, you may wish to look at the speed and convenience side of things. Of course, cars will usually be quicker than walking, and will enable you to carry more things; however, when travelling in a busy town with lots of traffic, sometimes walking can be easier. Furthermore, people can often walk in places cars cannot go, and there is no need to worry about parking, unlike when driving a car.
When walking, there are very few costs that you need to worry about. In fact, just about the only cost involved is the wear and tear suffered by any shoes that are worn whilst walking; however, this is a relatively minimal cost. On the other hand, running a car can be very expensive, with the need to pay for fuel, as well as any costs associated with taxes, insurance, maintenance, and more.
Therefore, cost can be a particularly interesting thing to compare when discussing cars and walking.
Another thing that you may wish to discuss when trying to write a quality comparative essay about cars versus walking is the issue of pollution. Whilst people who are walking may drop litter or pollute the environment in various other similar ways, when looking solely at the act of walking itself, there is very little pollution caused; however, the drivers of cars will often cause a great deal of pollution. Not only does the petrol used by cars create a lot of pollution, but the production of cars also creates a lot of pollution. Therefore, even environmentally friendly cars will have caused a great deal more pollution than someone who chose to walk instead.
In fact, these are just three possible ideas that you could discuss, although there are plenty of others that you can use in order to create a quality piece of work.