JK from Douglas County writes, “Are the lane lines on the highway that are half white and half black purposeful? At first I just thought it was how they repainted the lines but I am beginning to believe there is some purpose.”
These black lane lines are called contrast pavement markings (CPM) and are used to improve the visibility of the lane lines. What they do is provide a better contrast between the lane line and the pavement surface, especially on lighter-colored pavements. They also help during dawn and dusk. When the sun’s angle is low, such as during sunrise and sunset, its rays shine directly on the pavement markings, causing glare and thus reducing the visibility of the markings. The visibility of more traditional white lane lines as well as yellow lines on light-colored surfaces is improved with the use of black CPMs.
There are two common contrast marking designs currently used on highways - lead/lag and bordered. Lead/lag is where a 10-foot contrast strip follows a painted 10-foot white strip. Bordered is where a black edge is placed on both sides of a white line. It is more common to see lead/lag lines in Colorado. CPMs have been used for nearly 20 years and don’t just help human drivers in poor light or in adverse weather, but they're also becoming more and more crucial for lane-keeping assist systems and in autonomous vehicle detection systems.
The use of contrast pavement markings is becoming a national trend with most states expanding or adopting their use.
In a paper written by the Illinois Center for Transportation, researchers said:
“The safety effects of contrast pavement markings are of interest to all departments of transportation (DOTs) and highway agencies. Understanding the safety effects of contrast pavement markings as a crash-prevention countermeasure will add to the pool of engineering knowledge and provide design and operation engineers with a useful tool to reduce crashes on highspeed roadways, where roadway departure crashes (RwD) account for over 50% of fatal crashes.”
Contrast pavement markings are believed to provide a reduction of roadway departure crashes, based on the findings of that research. That reduction results in economic savings related to crash costs that greatly outweigh the additional cost of contrast pavement markings.
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Denver7 Traffic Expert Jayson Luber says he has been covering Denver-metro traffic since Ben-Hur was driving a chariot. (We believe the actual number is over 25 years.) He's obsessed with letting viewers know what's happening on their drive and the best way to avoid the problems that spring up. Follow him on Facebook, Twitter or Instagram or listen to his Driving You Crazy podcast on any podcast app including iTunes, iHeartRadio, Spotify and Podbean.
