Just a word of warning for the streets in downtown Williams.  There are the two main streets that are part of old RT 66.  They divide and become single lane one way streets.  Old Route 66 is a one way street for East bound traffic.  Railroad Ave. is a one way street for West bound traffic.  After you pass through the center of town Route 66 goes back to a two way and takes you back to Interstate 40.  Grand Canyon Blvd. (North) also takes you back to Interstate 40 (exit 163).