You should probably post this sort of thing under "Notebook" so it is easier to see corrections made (there are better posting options). "In 1985, the car was the most popular transportation method. Each person traveled, on average, 3199 miles per year by car. This trend continued until 2000, when the average distance traveled by car per person increased significantly to 4806 miles." --Because you are talking about all cars in transportation, you could either use "the car was" or "cars were" to describes it. --The statement is past tense, so you would use "Each person traveled" (or "People traveled") because it is something that already happened; in this case, already changed. --Use of "on average" begins and ends with commas in my example because it is added and can be omitted from the sentence. You could also say "each person traveled an average of..." --Too many commas and not enough periods to break up the run on sentence structure. When adding completely additional information that does not directly relate to the subject of a sentence, start another sentence. --I swapped the word "continued to 2000," to "continued until 2000" because you are stating that the first 'average' was the same all the way until the year 2000, where it then changed. --You would use 'distance traveled' in the final statement because you are stating the unit of measure (miles) after the number itself. --As you "travel by car" the statement is only adding 'per person' as additional clarification and would come after.

In 1985, the car was the most popular transportation method, each person travelled on average 5148 km per year by car and this trend continued to 2000, when the average distance travelled per person by car increased significantly to 7735 km.

In 1985, cars were the most popular form of transportation, and on average a person would travel 5148 km per year by car. This trend continued to 2000, at which time the average distance travelled significantly increased to 7735 km per year.