I am neither a teacher nor am i good at english but i can provide some information.
You shouldn't start a sentence with a conjunction(eg: but,so, etc...)
You should include a comma after "In our country" and leave out the "the" because you are talking about a wide range of short journeys, not a definite journey.In our country fuel is very expensive and the short journeys can cost us a lot.
"Sedentary" shouldn't be included in that same sentence because the points just do not link, the environment doesn't have anything to do with sedentary?So they contaminate the environment and become very sedentary.
Other experts please correct me if I am wrong.
Student or Learner