@article{ref1,
title="Laboratory visibility studies of directional symbols used for traffic control signals",
journal="Ergonomics",
year="1978",
author="Smith, Graham and Weir, Robin",
volume="21",
number="4",
pages="247-252",
abstract="<p>[Abstract unavailable]</p> <p>Language: en</p>",
language="en",
issn="0014-0139",
doi="",
url="http://dx.doi.org/"
}