An examination of residual distributions in ordinary least squares (OLS) household-based trip generation models.

It is shown that the residual distributions obtained from typical OLS household-based trip generation models do not comply with the assumptions inherent in the use of ordinary least-squares. In particular, heteroscedasticity is likely to occur invalidating the estimation of coefficient standard errors by OLS procedure. A typical trip generation model is examined and it is shown that the heteroscedasticity is related to a linear function of the independent variables in the model. A transformation is suggested which would appear to yield constant residual variance.