A signal of the
<a href="http://www-users.rwth-aachen.de/christoph.schmitz2/hpsignal.html">Hp
colour light system</a> seen at Gerolstein (on Cologne-Trier) on 9 October 2005.
Obviously it has two green lights at the top, the left one seems to be for the
Hp1 aspect (proceed, only a green light), and the right one for the Hp2 aspect
(slow, green above yellow), located right above the yellow light (at the
bottom).
<p>
Digital photo by
<a href="http://www-users.rwth-aachen.de/christoph.schmitz2/index.html">Christoph
Schmitz</a>
(<a href="mailto:christoph.schmitz2@post.rwth-aachen.de">christoph.schmitz2@post.rwth-aachen.de</a>)