Trucking: Truckers pay, rand mcnally milemaker, digit zip code

Question
Please tell me the difference between "Practical Miles" vs. "Rand McNally Miles"?  Is it significant?  I'm a student and looking for a trucking company to apply to.  I want the best pay package available.  Someone told me that under the Rand McNally option you could end up driving some miles for free?  Is that true.  Thank you.

Answer
Chuck, it's true.  There are several ways to calculate mileage.  Carriers will use one of the major software programs.
The two most common are:
Rand McNally MileMaker: http://www.randmcnally.com/rmc/tdm/tdmProductDetail.jsp?prod_id=milemaker&cmty=0
and;
ALK PCMiler; http://www.alk.com/pcmiler/pcmiler.asp
Within each software there are various settings that will change the routes they use to calculate miles.
Shortest miles will be car routes that mat be ok for a straight truck but not all roads that a semi can travel, or it will use absolute shortest routes regardless of the kind or quality of roads.
Practical miles are commonly used as a fair calculation but there are additional settings for toll avoidance, haz mat routes that avoid tunnels, 53' routes and doubles routes.
Some carriers only pay loaded miles while others pay for empty miles dispatched.
On each route one or the other program might show shorter miles than the other, but in my experience, on average Rand McNally tends to show shorter miles overall, and neither one will be the same as the hub miles that you actually run.  That's because they use the five digit zip code and reference a database that is calculated from some specific point within the zip code.  Some may use a weighted average population center, others may use the geographic center and there may be other methods as well.
So if you are going from the furthest point in one zip code to the furthest point in another one the software will probably short you but the reverse can also happen.  The effect is more pronounced in short haul operations since it can be 20 to 30 miles across a zip code zone.  On long haul runs it's less noticeable on a percentage basis.  To help address this most carriers will have a short haul premium either in a higher rate or a flat add on.  If you are looking at local or short haul work be sure that the lower total mileage is offset by a higher rate.
Hope this helps.
Jim