Export of TSS from highly impervious highway segments may be complicated by a number of interacting factors including wind action, vehicular deposit and removal, and atmospheric deposition. Data from our study indicate that TSS loads from impervious roadways (site I) can be fairly predicted using hydrologic variables (level-1 analysis). However, including bulk deposition data (level 2) or traffic conditions during storms (level 3) appears to greatly improve TSS estimates (Table 8). Runoff from site II drains mostly into a pervious shoulder but, in certain cases, it may bypass the pervious area and flow directly to its outlet point [31]. The pervious/ vegetated area helps attenuate TSS discharge, rendering the influence of TSS contribution from vehicular traffic not as obvious as it had been observed at the impervious site I. For roadways with low imperviousness and traffic volumes (site III), TSS loading is less sensitive to all component variables with some improvement made possible by including bulk deposition.