Disconnected vertical lines with Latex table using booktabs package

I want the vertical lines in my table disconnected like in the example below.

My attempt is getting me vertical lines like in the second table shown below, how can I reproduce the lines like in the example?

This is my code to generate my table

\usepackage{graphicx}
\usepackage{amsmath}
\usepackage{amssymb}
\usepackage{multirow}
\usepackage{array}
\usepackage{makecell}
\usepackage[table,xcdraw]{xcolor}
\usepackage{booktabs}
\usepackage{arydshln}


\begin{document}
\begin{table}[h]
\begin{center}
\setlength{\tabcolsep}{8pt}
\renewcommand{\arraystretch}{1.0}
\begin{tabular}{c|cccc}
\toprule
classes  & abs\_rel & a1    & a2    & a3    \\ \midrule
Road    & 0.138               & 0.851          & 0.917          & 0.946 \\ %\hline
Vehicle & 0.135               & 0.855          & 0.920          & 0.948 \\ %\hline
Lane    & 0.135               & 0.855          & 0.920          & 0.947 \\ %\hline
\bottomrule
\end{tabular}
\end{center}
\end{table}
\end{document}

You can replicate the incorrect usage of booktabs with vertical lines if you refrain form loading the arydshln package. This package would fix some of the incompatibilities of booktabs with vertical lines.

However please consider carefully if you really want your table to look like you made an error in coding it. It will look as if you don't know your latex.

\documentclass{article}
\usepackage{graphicx}
\usepackage{amsmath}
\usepackage{amssymb}
\usepackage{multirow}
\usepackage{array}
\usepackage{makecell}
\usepackage[table,xcdraw]{xcolor}
\usepackage{booktabs}
%\usepackage{arydshln}


\begin{document}
\begin{table}[h]
\begin{center}
\setlength{\tabcolsep}{8pt}
\renewcommand{\arraystretch}{1.0}
\begin{tabular}{c|cccc}
\toprule
classes  & abs\_rel & a1    & a2    & a3    \\ \midrule
Road    & 0.138               & 0.851          & 0.917          & 0.946 \\ %\hline
Vehicle & 0.135               & 0.855          & 0.920          & 0.948 \\ %\hline
Lane    & 0.135               & 0.855          & 0.920          & 0.947 \\ %\hline
\bottomrule
\end{tabular}
\end{center}
\end{table}
\end{document}

Here's an answer just for completeness. If your goal is to have the same gaps across the table, stick to booktabs.

However, custom gaps can be created without loading booktabs as long as they are added before tabular starts creating a new row. Essentially gaps become a part of a rule, not a part of rows/cells. It is achieved by a TeX primitive \noalign{}; it can only be used between rows! For instance, one can place the following line between rows

% ...
\hline \noalign{\vskip 3pt}
% ...

and get the 3pt skip below the \hline which breaks the vertical bar. Since you have added makecell package, \Xhline{<<rule size>>} is also available. Combined with \noalign{\vskip <<size>>} and you can have custom gaps with custom rules.

Here's the example where I made a convenient macros: \Gap and parametrised \XGap{<<size>>.

\documentclass{article}
\usepackage{makecell}
\NewExpandableDocumentCommand\XGap{m}{\noalign{\vskip #1}}
\NewExpandableDocumentCommand\Gap{}{\XGap{3pt}}

\begin{document}
\begin{table}[h]
  \begin{center}
    \setlength{\tabcolsep}{8pt}
    \renewcommand{\arraystretch}{1.0}
    \begin{tabular}{c | *4{c}}
      \Xhline{0.8pt} \XGap{1pt}
      classes & abs\_rel & a1    & a2    & a3    \\
      \Gap \hline \Gap
      Road    & 0.138    & 0.851 & 0.917 & 0.946 \\
      Vehicle & 0.135    & 0.855 & 0.920 & 0.948 \\
      Lane    & 0.135    & 0.855 & 0.920 & 0.947 \\
      \XGap{1pt} \Xhline{0.8pt}
    \end{tabular}
  \end{center}
\end{table}
\end{document}

The macros can be stack, repeated after each row and used with negative skips to achieve some special effects. For instance, consider this table

\begin{table}[h]
  \begin{center}
    \setlength{\tabcolsep}{8pt}
    \renewcommand{\arraystretch}{1.0}
    \begin{tabular}{c | *4{c}}
      \Xhline{0.8pt} \XGap{1pt}
      classes & abs\_rel & a1    & a2    & a3    \\\Gap
      \hline \Gap
      Road    & 0.138    & 0.851 & 0.917 & 0.946 \\\Gap
      Vehicle & 0.135    & 0.855 & 0.920 & 0.948 \\\Gap
      Lane    & 0.135    & 0.855 & 0.920 & 0.947 \\\Gap\XGap{-2pt}
      \Xhline{0.8pt}
    \end{tabular}
  \end{center}
\end{table}