Those familiar black-and-yellow road markers quietly tell drivers which direction to take around roadside obstacles.
That black-and-yellow striped marker you sometimes see along U.S. roads is more than a warning—it tells drivers which way to go around an obstruction.
Drivers encounter dozens of road signs and markers during a typical trip. Many are so familiar that motorists recognize them almost instinctively. Others are rarely seen, even though they can provide important information about what is ahead.
One example is the black-and-yellow striped marker used on or near roadside obstructions. In the U.S., these are classified as Type 3 object markers under the Federal Highway Administration's Manual on Uniform Traffic Control Devices, or MUTCD. They are used to identify obstructions within or next to the roadway.
The striped markers can be found near bridge supports, bridge abutments, guardrails, handrails, utility poles and other objects that could affect a vehicle's path. They can also mark roadside conditions such as narrow shoulders, drop-offs and abrupt changes in the road's alignment.
The most important detail is the direction of the diagonal stripes. They are set at a 45-degree angle and slope downward toward the side where traffic should pass the obstruction. In other words, the stripes essentially work like a built-in directional arrow.
It can be easy to overlook the purpose of these markers during daylight. If a bridge support or other obstruction is clearly visible, a driver may wonder why an additional marker is needed.
The situation changes at night or in poor weather. The yellow portions of these markers are retroreflective, making them much easier to see when illuminated by headlights. That gives drivers an additional visual reference to identify the edge of the roadway and the safe path around an obstruction before they reach it.
If an obstruction can be passed from either side, the MUTCD specifies a different Type 3 design with yellow-and-black chevrons pointing upward. The federal standard also allows directional signs to be used instead of an object marker when appropriate.