To enhance traffic flow stability, the intricacy dynamic of road geometry characteristics on traffic safety is explored in this paper. And an extended macro traffic flow model is proposed coupled with electronic throttle (ET) dynamics effect for a single lane system. Based on the linear stability analysis, we can distinctly find that the stable region will varies due to the change of slope angle when the electronic throttle opening angle is fixed. Characteristics of density wave propagation near the neutral stability lines are described by means of the KdV equation, which is obtain from nonlinear analysis method. The new model also captures the evolution characteristics of shock and rarefaction waves. The simulation example verifies that the road geometric characteristics have a marked impact on the total energy consumption of the transportation system. The traffic congestion can be restrained efficiently by introducing the ET dynamics effect. The numerical simulation shows a good agreement with the analytical result.