Why do some states install traffic lights horizontally? – Jalopnik

Traffic lights help promote traffic flow by allowing certain lanes to pass and others to stop. Some are more complex and include signals for buses. But ultimately, they are devices with red, yellow and green lights, designed to prevent accidents at intersections. You’d think there would be rules for how they should look and work, and you’d be right. However, they are not always the same.

As you drive through Ohio, you will see traffic lights mounted vertically on a light pole, with the red light on top. When traveling to Texas, the lights are often mounted horizontally on the pole, with the red light on the left. So what gives? Why are they different? It could be several things, including ease of movement, resistance to wind damage, or simply aesthetics.

A traffic light mounted on a pole above an intersection is sensitive to wind. If it is mounted vertically on that pole, there is a limited surface area to keep the light stable. Vertical lights also have a flat surface that is easily caught by the wind and moved. In some ways, you might think of a vertically mounted traffic light as a sail on a sailboat. If the gust of wind is strong enough, it can dislodge the lamp from the pole, damaging the lamp and the area around where it lands. When lamps are mounted horizontally, wind plays less of a role, reducing the risk of damage or injury.

Clearance is also a factor. Semi-trucks can be quite large, and engineers don’t want the trailer roof to rip the traffic light off its pole every time a truck drives under it. Signals must be at least 4.5 meters above the roadway. Mounting them vertically can save a few inches of space under the mounting post, and in some cases those extra inches can make all the difference. When the traffic light is under a highway overpass, there is a physical limit to how high it can be mounted due to the overpass. A horizontal orientation can also provide more breathing room around the mounting post in these situations.

On a viaduct, horizontal mounting can also improve the visibility of the signal. Structural elements of the viaduct are less likely to obscure the light.

For traffic lights that are closer to the ground, such as those mounted on poles on the side of the intersection, you will likely find that these lights are mounted vertically. Those are easier to mount vertically because there is less wind to worry about, and if mounted on the side of the road a vertical light would be easier to see by traffic. Some intersections even have lighting on a pole above the intersection and also on the sides.

The only real constant with traffic lights is that they have a red light, a yellow light, and a green light (unless it’s Japan, where the lights are blue instead of green). In addition, state and local governments determine how and where most of them are mounted. That’s why if you’re driving in one state, the lights may be mounted vertically, and if you’re driving in another state, they’ll be mounted horizontally. That’s also why you might notice cameras and sensors mounted on certain lights, but not others.

For example, in Washington State, traffic lights must be mounted vertically unless there is a clearance problem or to match the orientation of other lights at the intersection. The State Traffic Engineer must approve all horizontal installations. And in some areas, such as parts of Michigan, the traffic signal housings may be black, while in other parts of the state they are yellow.

Although specific signage is required nationally to look a certain way, many decisions are made at the local level. Now you have something new to think about while you stopped at the next red light.