[EN] This paper deals with optimizing embedded carbon dioxide (CO2) emissions using metamodeling, whether it is the deck of a lightened post-tensioned slab bridge or any other design structure. The main contribution of this proposal is that it allows optimizing structures methodically and sequentially. The proposed methodology is general and can optimize any structure with different objective functions. The approach presents two sequential phases of optimization, the first one of diversification and the second one of intensification of the search for optimums. Specifically, the type of concrete used, the amount of active and passive steel, the lightweight volume, and the area of formwork used. Finally, with the amount of CO2 emissions and the differentiating characteristics of each design, a heuristic optimization based on a Kriging metamodel is performed. An optimized solution with lower emissions than the analyzed sample is obtained. If CO2 emissions were to be reduced, design recommendations would be to use slendernesses as high as possible, in the range of 1/30, which implies a more significant amount of passive reinforcement. This increase in passive reinforcement is compensated by reducing the amount of concrete and active reinforcement. Another important conclusion is that reducing emissions is related to cost savings. Therefore, optimizing the cost would be sufficient to reduce the environmental aspects. Furthermore, it has been corroborated that for a cost increase of less than 1 %, reductions for emissions emitted into the atmosphere of more than 2 % can be achieved., Grant PID2020-117056RB-I00 funded by MCIN/AEI/ 10.13039/501100011033 and by ERDF A way of making Europe.