One of the most important research interests in the automotive sector is energy consumption and pollutant emissions reduction. Usage developments are continuing in parallel to technological evolution to maximize the efficiency of the system. One of the recent methods in usage field is eco-driving. It refers to a fuel economic driving behaviour which is the result of a trajectory optimization. In this research a parametric study on the impact of some optimization constraints on the optimal operation of a gasoline powered vehicle is presented. A vehicle model is described and the optimization algorithm based on dynamic programming is introduced. The optimization results on a defined trajectory under different road and trip constraints are discussed in this paper. These constraints include trip time and road grade, as well as the impact of state discretization. With the results, impact of these constraints on fuel consumption and CO2 emissions is presented and the trade-off between fuel consumption and trip time is discussed. The results show that optimal vehicle operation vary depending on road and trip constraints.