With the surge of human population, the need for transportation of goods and people also concomitantly increases, resulting in urban air pollution through emission from motorized traffic especially in developing countries. The extent of environmental pollution in an urban setting is significantly influenced by the pollutants of vehicular fuel combustion. Many effective measures are required in cities to sequester carbon thereby helping to reduce automobile pollution. Roadside greeneries can serve as ecological elements which reduce the concentration of pollutants from vehicular emissions by their direct involvement in absorbing vehicular emitted carbon. In this context, in this study an attempt has been taken to assess contribution of roadside greeneries in absorbing vehicular carbon dioxide emission. A case study has been conducted on arterial roads of mega city Dhaka to quantify the vehicular carbon emission and correlate it with roadside trees to absorb the emitted carbon dioxide. It is noted that in Dhaka city, carbon dioxide is accounted for more than ninety percent of air pollution. To achieve our goals, two busiest arterial roads (namely Mirpur Road and Rokeya Shoroni Road) were taken into account to quantify vehicular carbon emission as well as assess carbon absorption by roadside greeneries. Carbon absorption by different sizes of trees has been quantified using the amount of woody biomass. In addition, absorption by grass-shrubs-herbs has been quantified by the area they cover. The results thus obtained show that indeed the road with more side greeneries absorbs more vehicular emitted carbon dioxide. It is therefore evident that plantation of more roadside trees is an effective measure of reducing air pollution and consequently turning a city to become healthier and more suitable for living.