Heidi Willuhn, age 11, of Rockford, Illinois, for her question:

Do numbers on federal highways show north south, east west?

Strictly speaking, they are Interstate Highways. Their numbers do tell whether they run east west or north south. The number also may tell whether you are near the Pacific or the Atlantic, the Canadian or the Mexican border. If an Interstate Highway has an even number, you can depend on it to lead you east or west. If it has an odd number, it can take you north or south. It carries its number on red, white and blue markers. The standard marker is a blue shield, bearing the number in white, with the word 'Interstate" on a red band across the top.

Each of these routes is part of a linked network called the National System of Interstate and Defense Highways. The numbering systems begin in the south and the west. The lowest east west number is near Mexico, the highest near Canada. Interstate Highway 5 runs near the Pacific, the odd numbers get higher toward the Atlantic