To my understanding, newly applied pavement markings are expected to meet the ASTM D 6359
(250 millicandela (mcd) minimum for white, and 175-mcd minimum for yellow). The material
slowly degrades over time. At this point, no minimum level of retro reflectivity has been set.
According to past studies, most motorists report that the stripes become more difficult to see
when the retroreflectivity falls between 80-100 mcd.
The Excel spreadsheet (NC summary.xls) shows the average values for the sections of roadway
in your region. Due to the variability in striping and the retroreflectometer used for collecting data,
an average over a stretch of roadway is the best way to observe the values. Here is an example
of the retroreflectivity across an entire section. This data was collected on 8/20/2003. This stripe
was painted on 4/28/2003. It appears to be maintaining its retroreflectivity with an average value
2
of about 200 mcd/m /lx.
SR 2 WB MP 138-128 White Edge Line
300
250
Retroreflectivity
(mcd/m^2/lx)
200
150
100
50
0
126 128 130 132 134 136 138 140
MP
We will collect more data from these sections of roadway through the fall and winter to observe
how the paint stripes degrade as time passes. I also attached another spreadsheet
(Nccomparison.xls) comparing the sections of roadway in your region with data collected in other
regions. I grouped the information by the AADT for the sections of roadway.