\usepackage{tikz}

\mode<presentation>

\setbeamertemplate{title page}
{
	\usebeamerfont{title}{\usebeamercolor[fg]{title}\inserttitle}\par
	\usebeamerfont{subtitle}{\usebeamercolor[fg]{subtitle}\insertsubtitle}\par
  \bigskip
  \usebeamerfont{title}{\usebeamercolor[gray]{title}\hrulefill\par}
	\bigskip
	\usebeamerfont{author}\insertauthor\par
	\usebeamerfont{institute}\insertinstitute\par
	\usebeamerfont{date}\insertdate
}

\mode<all>
\endinput