The year 2000 radiative forcing (RF) due to changes in O₃ and CH₄ (and the CH₄-induced stratospheric water vapour) as a result of emissions of short-lived gases (oxides of nitrogen (NO_x), carbon monoxide and non-methane hydrocarbons) from three transport sectors (ROAD, maritime SHIPping and AIRcraft) are calculated using results from five global atmospheric chemistry models. Using results from these models plus other published data, we quantify the uncertainties. The RF due to short-term O₃ changes (i.e. as an immediate response to the emissions without allowing for the long-term CH₄ changes) is positive and highest for ROAD transport (31 mW m^-2) compared to SHIP (24 mW m^-2) and AIR (17 mW m^-2) sectors in four of the models. All five models calculate negative RF from the CH₄ perturbations, with a larger impact from the SHIP sector than for ROAD and AIR. The net RF of O₃ and CH₄ combined (i.e. including the impact of CH₄ on ozone and stratospheric water vapour) is positive for ROAD (+16(±13) (one standard deviation) mW m^-2) and AIR (+6(±5) mW m^-2) traffic sectors and is negative for SHIP (-18(±10) mW m^-2) sector in all five models. Global Warming Potentials (GWP) and Global Temperature change Potentials (GTP) are presented for AIR NO_x emissions; there is a wide spread in the results from the 5 chemistry models, and it is shown that differences in the methane response relative to the O₃ response drive much of the spread.