¿Cómo puedo darle forma exactamente?

Question

Estoy intentando dibujar el coche como referencia. Pero va muy difícil. No entiendo la idea ni la solución correctas. Aquí está mi coche de referencia.

\documentclass{article}
\usepackage{tikz}
\usepackage{pst-plot}
\usepackage{pst-eucl}
\usepackage{amsthm}


\usepackage{environ}
\makeatletter
\newsavebox{\measure@tikzpicture}
\NewEnviron{scaletikzpicturetowidth}[1]{%
  \def\tikz@width{#1}%
  \def\tikzscale{1}\begin{lrbox}{\measure@tikzpicture}%
  \BODY
  \end{lrbox}%
  \pgfmathparse{#1/\wd\measure@tikzpicture}%
  \edef\tikzscale{\pgfmathresult}%
  \BODY
}
\makeatother

\makeatletter
\newcommand*\setupscalewithtikz[1][\linewidth]{%
\newsavebox{\box@tikzpicture}
\newlength{\newwidth}
\setlength{\newwidth}{#1} 
}
\NewEnviron{tikzpicture*}[1][]{%
  \begin{lrbox}{\box@tikzpicture}%
  \begin{tikzpicture}[#1]
     \BODY
  \end{tikzpicture}% 
  \end{lrbox}%
  \pgfmathsetmacro\width@scale@picture{\newwidth/\wd\box@tikzpicture}%
  \begin{tikzpicture}[#1,scale=\width@scale@picture]
    \BODY
  \end{tikzpicture}% 
}%
\makeatother

\begin{document}
  \begin{figure}
      %\centering
      \begin{center}
      \begin{scaletikzpicturetowidth}{.8\textwidth}
          \begin{tikzpicture}[scale=\tikzscale, declare function={
              excitation(\t,\w) = sin(\t*\w);
              noise = rnd - 0.5;
              source(\t) = excitation(\t,20) + noise;
              filter(\t) = 1 - abs(sin(mod(\t, 50)));
              speech(\t) = 1 + source(\t)*filter(\t);
            }]
            \draw
            [draw=black,rounded corners=6ex,very thick] (3.6,0.5) -- (1.5,.5) -- ++(0,2.5)-- ++(3,0);% --  ++(15,0) -- ++(0,-2.5)--++(-2.5,0);
            \draw[draw=black,rounded corners=5ex,very thick](14.1,3) -- (16.1,3) -- ++(0,-2.5) -- ++(-2.1,0);

            \draw[draw=black,rounded corners=1.2ex,very thick](6,0.5)--(11.6,0.5);

            \draw[very thick, rounded corners=5ex,thick]  (4.5,3) -- ++(2,2) -- ++(6.6,0) -- ++(1,-2);


            \draw [draw=black,very thick](6,.5) arc (0:180:12mm);
            \draw [draw=black,very thick](14,.5) arc (0:180:12mm);


        \end{tikzpicture}
        \end{scaletikzpicturetowidth}
      \end{center}

      \caption{Sensitivity analysis for cut Model of car}
      \label{fig:sens_1ncar}
  \end{figure}
\end{document}