For some of the volume studies, there are two files.  One is labeled normally, 
and the other has "(axle)" at the end of the file name. The software that 
analyzes the raw data files loses accuracy for studies over 5,000 vehicles/day 
when using layout #41, #51, or #52. In these situations, the data must be 
analyzed using axle counts only, as in layout #11 or #21. Therefore, the "axle" 
studies should be used to more accurately determine vehicle volumes for roadways
with ADT's of 5,000 or more.

Speed and vehicle classification studies are not really effected as they deal 
in percentages instead of totals.

In addition, some studies with bi-directional volumes will also be analyzed as 
"total" volume studies with "axle" at the end of the name.  In some situations, 
the analysis software does not achieve a very high accuracy in matching up axle 
hits on the tubes.  In these cases, applying the directional split percentages 
to the total volume provides a more accurate volume number.