This changed the way cities are because cities are usually built to accommodate highways and roads. Built in and around highways have changed the main structure of present-day cities.
Is this a multiple choice question..?
Add some more information!
In a way, this is a double edged sword. On one hand, the animals are needed to best test the effects, but on the other hand it can be seen as very unethical. Honestly, I don't really see a way around using the animals. Unless you get human volunteers, but there is no way to fully make them understand what they are getting themselves into which can turn unethical very, very fast. If all of a sudden one of your human volunteers decides that they do not want to be a part of the test anymore, there is noting you can do to reverse what has already been done.
