@article{ref1,
title="Photographic technique for estimating skid number and speed gradients of pavements",
journal="Transportation research record",
year="1977",
author="McDonald, L. Bruce and Blackburn, Robert R. and Kobett, Donald R.",
volume="633",
number="",
pages="13-21",
abstract="A technique has been developed for determining skid number and speed gradients of pavements from a moving vehicle. Photographs were made of the pavement by using a light at low-incidence angle to project shadows across the peaks and valleys of pavement macrotexture. The photographs were compared to standard photogrpahs of pavements with known gradients. The ratings were converted to estimated skid number and speed gradient by using a regression equation. The technique is economical, valid, and reliable.<p />",
language="en",
issn="0361-1981",
doi="",
url="http://dx.doi.org/"
}