Another reason that public transportation is the best solution to traffic jams is because it is so economical. People want to use public transportation instead of driving their own car because they can save money. Public transportation usually does not cost very much, especially for people who use it often. There are discounts for seniors and students, which makes it an even more economical way for these groups to travel around town. Using public transportation also eliminates the need to pay for parking, car insurance, and car maintenance, not to mention gasoline. All of the expenses related to owning a car are replaced with one simple fare. Because it is so economical, public transportation is a good solution to traffic jams by encouraging more people to travel together and reduce the number of cars on the road. What component of problem- and-  solution structure is this?