  This paper proposes an improved Intelligent driving model (Sigmoid-IDM) to
address the problems of excessive acceleration in traffic oscillation and
following failure in free flow. The Sigmoid-IDM uses a Sigmoid function to
enhance the start-following characteristics, improve the output strategy of the
spacing term, and stabilize the steady-state velocity in free flow. Moreover,
the model asymmetry is improved by means of introducing cautious following
distance, driving caution factor, and segmentation function. The
anti-interference ability of the Sigmoid-IDM is demonstrated by local stability
and string stability analyses.
