Complex sentence: Since August 24,2001, they have been numbered in a scheme somewhat similar to that of the Interstate Highway System in the United States; the symbols of the South Korean highways are similar to the US red, white and blue.
Split into simpler sentences: Since August 24,2001, they have been numbered in a scheme somewhat similar to that of the Interstate Highway System in the United States. Furthermore, the symbols of the South Korean highways are similar to the US red, white and blue.