No trucks! Satellites crossing.

What in the world does this sign, found in the UK, mean?

According to Sky News, this sign means that trucks should not use their GPS systems to navigate on the signed roads. Apparently, the roads are very narrow and the GPS is not accurate enough to properly guide them. But why is the red line over the truck? Shouldn’t it be over the satellite? Or would that mean “Trucks, activate weapons and destroy all satellites.”

Road signage, thankfully, has been an area that both traffic engineers and human factors engineers have long been involved with (see the Federal Highway Administration). Most road signs in the US are clear. More text may be useful in some occasions (except for signs that say “PED XING”, which means “Pedestrian Crossing”), but images are also extremely useful.

The goal is to get drivers to immediately understand what the sign says. Reading is automatic (the Stroop effect; Stroop, 1935), but it still takes time to process the words. On the other hand, images are wonderful because the gist of an image can be determined in mere milliseconds (Potter, 1976; Friedman, 1979) - complex scenes can be reduced to words like “library” or “bedroom” in the blink of an eye. This is what gives images the advantage. A well-designed image must be easily viewed, and the gist must be extracted quickly. If the sign is confusing - such as the one above - by the time drivers understand the sign, it may be too late.