One of the global issues of air pollution is global warming. Greenhouse gases (GHGs) prevent the Sun's rays from returning back into space from the Earth's surface. Transport is the main source of GHG emissions whereby CO2, CH4and N2O gases released into the atmosphere from the consumption of fossil fuels by cars. This study has been conducted in Tehran, in 2010, with the aim of determining the quantity of emissions resulting from the implementation of the Bus Rapid Transport (BRT) systems as compared with conventional buses.The research methodology is based on the method of the IPCCand using Global Emission Factors. By employing statistics obtained from the Bus Company in Tehran and the Department of the Environment, emissions per passenger, emissions from the BRT system, baselines emissions, and emission reductions due to the introduction of the BRT system in Tehran, have all been calculated for 2010. The results of this calculation show that emissions per passenger in the BRT System, on Lines 1, 4 and 7, respectively, are 188.9, 189.1 and 282.7 (gr/p). The total amount of the BRT system’s emissions in the same lines is, respectively, 3.3×1010, 0.3×1010 and 3.1×1010(tCO2 e). Baseline emissions would be 7.5×1010, 1.4×1010 and 4.8×1010(tCO2 e) if those passengers wish to be transferred by conventional buses. Emission reductions achieved by the BRT system on these lines are 4.2×1010, 1.1×1010 and 1.7×1010(tCO2 e).Results have shown that the average emissions reductions per passenger made by the BRT System over the conventional system is 300 grams per passenger. The total average amount of emissions reductions has been 2.3×1010(tCO2 e), so the BRT system, in addition to raising the quality of the transport, also reduces the level of GHG Emissions compared to the conventional system.