Aerosols and their precursors are emitted abun-dantly by transport activities. Transportation constitutes one of the fastest growing activities and its growth is predicted to increase significantly in the future. Previous studies have estimated the aerosol direct radiative forcing from one trans-port sub-sector, but only one study to our knowledge esti-mated the range of radiative forcing from the main aerosol components (sulphate, black carbon (BC) and organic car-bon) for the whole transportation sector. In this study, we compare results from two different chemical transport mod-els and three radiation codes under different hypothesis of mixing: internal and external mixing using emission inven-tories for the year 2000. The main results from this study consist of a positive direct radiative forcing for aerosols emit-ted by road traffic of +20±11 mW m −2 for an externally mixed aerosol, and of +32±13 mW m −2 when BC is inter-nally mixed. These direct radiative forcings are much higher than the previously published estimate of +3±11 mW m −2 . For transport activities from shipping, the net direct aerosol radiative forcing is negative. This forcing is dominated by the contribution of the sulphate. For both an external and an internal mixture, the radiative forcing from shipping is esti-mated at −26±4 mW m −2 . These estimates are in very good agreement with the range of a previously published one (from −46 to −13 mW m −2) but with a much narrower range. By contrast, the direct aerosol forcing from aviation is estimated to be small, and in the range −0.9 to +0.3 mW m −2 .