Engineers explain the four main reasons behind the altered layout.
All over the world, the most common configuration for traffic lights is a vertical one, but a select few states in America - most notably Texas, Florida, Nebraska, and New Mexico - mount theirs horizontally, and the reasons behind doing so vary depending on the place and its climate. To understand what these reasons are, YouTuber Road Guy Rob did some digging with local authorities and discovered that there is no hard and fast rule to these differences in design; it depends on a number of factors.
The main reasons are clearance, cost, and visibility. And since some road users may be color blind, there are rules governing the orientation of stoplights too. Let's take a look at the factors contributing to an unusual stoplight configuration.
One of the big factors is a lack of clearance, and the presenter cites a Californian freeway interchange that was built atop an existing intersection. Here, despite the fact that most Californian stoplights are vertically mounted, the lights are horizontal so that they can give more clearance to vehicles passing underneath, like trucks. The only other solution would have been to raise the bridge, and that would cost millions more in raw materials and labor. Therefore, horizontal stoplights were the most cost-effective solution. Similarly, a horizontal signal head can be mounted slightly lower, which saves just a little bit of metal on each mast. Over thousands of traffic lights in a state, those little bits add up.
Another big factor is the climate, which is why some coastal states prone to high winds and hurricanes - like Florida - opt for horizontal stoplights. This design is less draggy and more aerodynamic, which prevents the signal head from being dislodged or bent. It also places less strain on the mast itself. We've seen the benefits of a sleek aerodynamic design on cars like the Lucid Air, and the benefits apply to fixed objects too.
Local preference can also play a role, and then there's the surrounding architecture. An intersection's lights could be obscured by a bridge, so in some cases, mounting the lights horizontally simply makes it easier for the lights to be seen from a distance. But how will a color-blind person know which light is red? For out-of-towners, too, this can be confusing.
As with anything else, there are basic rules and regulations. In traditional stoplights, red is on top, followed by amber, and then green. Following the same logic that English speakers use when reading (start at the top of a page and work from left to right), the first light on the left is always red and the furthest on the right will be green. Other standards given in the Manual on Uniform Control Devices include that horizontal stoplights must be mounted at least 15 feet off the ground to clear tall vehicles but no higher than 25 feet. Similarly, the signal head must be between 40-180 feet from the driver and within a conical window of 40 degrees from the driver's line of sight at the stoplight line.
In the future, the design will be less important than how the architecture communicates with traffic, but we'll always need a visual aid as a backup. Unless autonomous driving technology finally makes it to market.
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