The parameter estimates for two different analyses are
included in Table 5 The fit of the first model, which only
includes maintenance costs, is once more excellent with
R2 ¼ 83% and the results from general specification tests
(heteroscedasticity, non-normality and outliers) reveals no
model misspecification.
The track length coefficients bpy
and byy; are significantly
different from zero, but the corresponding coefficients for
traffic load bpu
and buu are not. Still, the bpu
coefficient has