It was Waylon Jennings instead of REO Speedwagon, but that was okay with Tim. Waylon was followed by Shooter Jennings and Marty Stuart. The two men in the mud-streaked Dodge Ram listened and watched the highway roll. Seventy miles up the line, the old guy pulled over, gave Tim a tip of his Case cap, and wished him a real fahn day.
This section is from the book, The Institute by Stephen King, chapter 2. What does "up the line" mean here? Thanks for your help!