• Tips on examining data: 3 road sign displays

    A bright road sign is highly visible at sunset, and other traffic signs are visible in the background.

    • Many decisions, especially purchasing decisions, rely on data. When you’re responsible for public safety and road safety, your decisions can affect people's lives.

      To make an informed decision which best serves the needs of the public, always consider the bigger picture and be sure to dive into data being presented. If information appears questionable or irrelevant, you may want to take another look.


    1. Performance graphs (do they always stack up?)

    • As the old saying goes, “A picture is worth a thousand words.” And when it comes to comparing the performance of various products, graphed data is often an effective means of quickly showing a reader how they stack up, right? Well, maybe not always.

      For example, take a look at the graph reproduced below from a sales brochure. Note that the graph is reproduced as it originally appears in the brochure, except that the name of the publisher has been removed.

    A graph suggests a competitor’s sign performance is superior to 3M’s sign performance.

    A graph of retroreflective sign sheeting performance?

    • The graph is used in the context of the brochure’s message about the effects of sign sheeting orientation (the direction the sign is mounted vs. sheeting manufactured direction) on retroreflective performance.*

      It looks like straightforward data that favors one product over another, but looks can be deceiving.

    What does the graph show? What does it NOT show? (7 questions to consider)

    • When presented with data visualized in this way, the common question is “What does the graph show?” But you should also ask yourself, “What does the graph NOT show?” Let’s take a closer look.

      After a close inspection, you may be left wondering:
       

      1. Which retroreflective sheeting products are represented by this data
      2. Are these products directly comparable? Do they belong to the same ASTM D4956 Type or different Types?
      3. What are the units of measurement on the horizontal and vertical axes?
      4. Why is the spacing on the vertical axis not uniform? (Hint: Using larger increments of space near the top of the graph exaggerates differences.)
      5. What combination of entrance and observation angles were used? After all, retroreflective sheeting performance can change dramatically depending upon the angles used in the measurement.
      6. Does this data represent performance for the same products at other entrance and observation angle combinations of interest? Or perhaps for all products?
      7. If this data shows “normalized” performance, what are the ACTUAL retroreflectivity values for the samples?

      The list of questions could go on, but the point is this: a graph may give an impression of performance differences, but it can still fail to provide the whole picture.

    Ensure data is complete, accurate and scientifically valid

    • When meaningful information is missing, it leaves room for false interpretations. So, to make informed decisions, always ensure the data you’re reviewing is complete, accurate and scientifically valid.

      To learn more about retroreflectivity, check out “What is Retroreflectivity and Why is it Important?”


    2. Photos of reflective signs (do they tell the whole story?)

    • In a low-angle photo of three highway signs, some letters are less bright, making the signs difficult to read.

      Have you seen this photo of real road signs?

      When you’re responsible for public safety on roadways, you know your decisions can affect people's lives. So, when you’re presented with an image of road signs with some dimmed (non-uniform) letters, you take notice.

      We do too. And that’s exactly what happened when we saw the image in a manufacturer’s brochure. To us, something just seemed odd about it. We decided to investigate to find these exact signs and better understand what’s happening in the photo.

    See the signs for yourself (Thank you, Google™ Maps.)

    • After some digging, we found them. This Google Maps link takes you to a ground view of the same signs in the daytime, so you can see for yourself the different angles from the photo could have been taken.

    Sign pitch... from a ditch?

    • Now, take note where a photographer might have been standing for this angle.
       

      • Was the photographer on the main roadway?
      • Would a driver on this main highway ever view the sign from this perspective?

      Strangely, the photo in question appears that it may have been taken from the frontage road next to the main highway or perhaps from the nearby shoulder. While we can’t make an exact match, we’ve approximated the same pitch and perspective to help provide some context to the photo.

    Google Maps image of the same highway signs shows the other photo was likely captured from a frontage road or a ditch.

    Why show this image?

    • While the photo was intended to reinforce a story about how sheeting orientation affects the appearance of overhead signs, there are inherent problems:
       

      • From what perspective was the image taken?
      • Is the perspective relevant to drivers?

    Consider the perspective of the driver

    • Because critical decisions are made on the roadway, the perspective of the driver should be taken very seriously. We know the driver is on the road, what direction they’re traveling, where their headlights are likely to be—all of this information is critical to optimizing safety and driver experience in a maximum number of scenarios.

      The photo may create an impression of performance differences, but it falls short of providing meaningful information given its estimated irrelevance to an actual driver on the highway.


    3. Reflective sign demonstration (have you seen a spinning road sign?)

    You may have seen this image or even witnessed a spinning sign demonstration. Let’s shed some light on what it means and how it connects—or perhaps doesn’t—to the driver experience.

    • Two octagon-shaped signs are next to each other; the first is uniformly bright, and the second varies in brightness.

      What is the spinning sign demo?

      In this demonstration, two signs are displayed: one with one manufacturer’s reflective sign sheeting, and another with a competitor’s sign sheeting. Then both of the signs are spun.

      As it spins, the competitor’s sign “blinks” between brighter and dimmer sections, potentially leading observers to believe that road signs in the field may blink too.

    So what? 5 questions to ask yourself.

    • Immediately, you might wonder:
       

      • Are the two sign sheeting products of the same class?
      • Are they being used per the manufacturer’s recommendation?
      • What’s the intended effect of the demonstration?
      • Do they want you to believe that this blinking is caused by a performance disadvantage?
      • Are they suggesting it’s a real problem?

      Let’s explore the concept in a comparable context: books.

    An analogy: omnidirectional books

    • Two people are sitting next to each other; one has an upright book, and the other has a sideways book.

      Just like a fixed road sign, a book conveys information, and is typically read in an upright position.

      If you turn a book sideways (change its orientation), it’s harder to read, and is therefore less effective in doing its job (communicating information).

    • Two people are sitting next to each other; one has an upright book, and the other has a spinning book.

      With an “omnidirectional book”—one that would feature new letters and symbols that could be rotated—one could theoretically “spin” it to demonstrate how it could be read from an angle. While this might have a “wow” factor, the question would become: what problem does it solve?

      Of course this is a ridiculous example, but it illustrates the false problem of the spinning sign demonstration.

    Road signs won't spin

    • A sign mounted to a post will not spin or blink.

      Likewise, when you sit down to read, you position yourself and the book in a fixed position that’s most comfortable for you to read.

    Optimize signs for the driver's maximum benefit

    • On the roadway, there are known factors. The direction of the sign is known, and it’s known how the sign will be positioned relative to vehicles.

      With this knowledge, sign sheeting can be optimized for the driver’s maximum benefit. In the end, only the driver needs to be able to read these signs to make critical driving decisions.


    Recommendation: all sign sheeting of the same color and on the same sign should be oriented in the same direction

    • To ensure the best driver experience, it’s recommended that all sign sheeting of the same color and on the same sign be oriented in the same direction (ideally in the 0 or 90-degree orientation). This ensures the best driver experience and finished sign appearance.


    Want to learn more about sign uniformity?

    • Dive deeper into what “orientational uniformity” is and what role it plays in the efficiency of reflective sign sheeting.


    • Disclaimer: Some photos and reference materials in this blog are from a competitive reflective sheeting manufacturer

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