Reducing fuel consumption and pollutant emissions is in high demand in the transportation sector. Developments in technological fields for having a most efficient drive train are continuing parallel to usage developments. Eco-driving is one of the recent methods to maximize the efficiency of the system by direct action of the driver. It refers to a fuel economic driving behaviour, which is the result of a trajectory optimization, to minimize fuel consumption for road vehicles.In this research we have performed a parametric study on the impact of some road and trip constraints on the optimal trajectory. The algorithm is based on dynamic programming for finding the optimal vehicle operation. Given a drive cycle, or a short defined trajectory, the optimal operation is calculated under different constraints such as trip time or road grade. The results show that optimal vehicle operation vary depending on road and trip constraints.