What goes bump every night on roads?

        Have you ever wondered about the reflective bumps in the middle of the road and why they are colored differently? These bumps are called Reflective Pavement Markers or Raised Pavement Markers (RPMs) and they serve a meaningful purpose. They come in six varieties of colors: red, green, blue, yellow, white, and then a combination between white and red. The red RPM shows that you are going the wrong way while white RPMs mean that you are going the right way down the road. Now you might ask what about the green and blue RPMs shown in the photo above? The blue are placed to catch the eye of an emergency vehicle driver and indicate the presence of a hydrant on the side of the road. Green serves many purposes, such as indicating a gated community's entrance for a emergency vehicle, utility company's roadside installation site to help their driver find it quickly, etc. They are made to withstand cars that may run over them, so they are naturally tough to move if not impossible. There are some that can be loose. These loose RPMs can be fatal as I found while researching their importance in other countries since a DJ was killed by a "cat's eye," as they are called in British areas due to their reflective nature being similar to a cat's eye when lit up at night. Not only are these RPMs used on the road, they are also used to show mailboxes at night, trail markers, and even art.
        The history of these RPMs starts back in 1934 with a British man named Percy Shaw who patented the "cat's eyes." The significance of these "cat's eyes" were made apparent during World War II because of the blackouts. In the 1960's, California came to have a fad of the road markers called Bott's Dots. These markers weren't usually reflective but described as "driving on Braille" if you ran over them. The modern RPM was born with an initial 1964 patent application, followed by another patent granted in 1986 that addressed the unique design requirements of any object that sits outside for the whole year on a busy road.
        What might I hear while I am close to these RPMs? Nothing unless I am in a moving vehicle. They make an annoying sound when you run over them and it can sound like you are riding with a flat tire. What do I see when a light reflects on it's surface? Well, it depends as I said before. I might see a soft red, white, blue, green, or yellow light reflecting back at me. What do I think when I look at these little bumps? I think nothing of them in the day time, but at night they are lifesavers since some lines aren't exactly well painted.

References: http://www.slate.com/blogs/the_eye/2014/01/23/what_s_that_thing_a_brief_history_of_reflective_pavement_markers.html

Bott's Dots













Night View of a road lit up with RPMs.

Art using raised pavement markers in a pedestrian tunnel at the Belleview RTD Station in Denver, Colo., 2008