Thanks a lot for your suggestions again Jay.
The cost impedance I am attempting to accumulate with the OD Cost matirx is distance in kilometers.
Essentially I have 4 different road classes, which a different distance factor applies to each segment of rad class, for example:
A Class = distance(km)*1 = 10km
B Class = Distance(km)*1.25 = 2km
C Class = Distance * 2 = 4km
Length = whish is the geometric length of the segment (km)
Essentially the output w should be
A = 10km
B = 2.5km
C = 8km
Length = 16km
The resulting attributes have in the past accumlated the distances correctly but I am still at a loss as to why they are not now.
After undertaking the same process using the Closest facility option with the same networjk dataset, the distances accumlate correctly! I guess this is a solution to the problem, however if you have any ideas as to why the OD cost matrix may not be accumulating correctly please let me know.
Thanks again Jay!