by IncanusGURPS has a pretty much detailed set of rules fo overland long distance travel on page B187; however, the way they are written in the Basic Set can leave one pretty confusing, and it's quite difficult to find the information you need quickly. Also, it covers only general long distance travel, like which could be expected from a slow-moving caravan or an adventuring party not in the hurry, but are inadequate in situations when a long distance must be covered quickly -- this is described under Running, exactly 99 pages earlier in the book.
To make things easier for me and my players, I have designed a small table which covers most of the situations that can arise when traveling long distances, using primarily muscle power, on an Earthlike world. The table requires you to have the freely available Adobe Acrobat Reader.
You can download the LongDist.pdf here (112 kB).