There ain't no speed limits outSol.
According to Chapter 7, Section 1.13 of the TCID's official travel manual, "The Asteroid Highway is the pathway set aside for the transit of asteroid from Out Sol, after their re-navigation by the massive Hooker ships and en route to The Dot (where they are consumed in the gravity well and realized as energy by Earth and Mars)."
Well ain't that somethin'.
Let me try and simplify this for y'all: The Asteroid Highway is couple hundred miles high and a buncha millions of miles long and wide. It cuts its way through the solar system using the gravity of large objects and planets (like big assed Saturn and Jupiter) to push masses of stuff into a long, dense tube of material aimed at the magical and mysterious Dot. Oooh!
All along the Highway you'll see Multicorp ore stripper ships and their contractors. These dudes extract ore for transport by cargo ships and, eventually, they'll head off for processing in high earth orbit factories. Multicorp security patrols the highway for broken down ships, ore pirates, and unauthorized stripping. (claim jumping, that is. Ya perv.)
The Asteroid Highway finally ends at Mars Station, where feeder rigs do the final renavigation and spin the material all nice and tidy -like into The Dot, creating a nice flow of mass and light and energy so ya'll can live happily ever after.