I-610 around Houston, January 29, 2012
The first 20,000 miles are the easiest.
According to Clinched Highway Mapping, I have now traveled approximately 45% of the entire interstate highway system in the United States.
To put into perspective how difficult the remaining 55% will be to reach, let me put it this way: The new interstate mileage required to reach the 50% threshold is greater than my untraveled mileage in Arkansas, Illinois, Indiana, Minnesota, Missouri, North Dakota, Ohio, Oklahoma, South Dakota and Wisconsin combined.