
So what they did, I imagine, is look for the brightest signal within the basic design prior to having added any controls. Once they had identified that location, they placed the most commonly-used control there.
Where else might we look for examples of this "signal location effect"?
Take a look at this picture; what types of vehicles can you see?


Here’s another view of a school bus, a Type A. The brightest signal is the words “SCHOOL BUS” at the top center. What makes them bright? Mostly these contrast effects-
Size- They are the largest letters
Case- "All caps" carries a connotation of importance
Location- Right in the middle of the top zone.
So what’s the problem? Redundancy. Most drivers already know this is a school bus, in fact we could identify one of these by shape, color or size. Why is redundancy a problem in this case? Because if you read the back of a school bus, you’ll see at least three other pieces of information that are actually quite important. They are safety-related, and violating them could cause injury and/or a hefty fine to the violator. And the bright signal of the "SCHOOL BUS" sign overwhelms these other pieces of information.
Take a look at this one. You should be able to see the following items that drivers need to be aware of;

· Unlawful to pass info- $250 fine AND license suspension for first offense
· Railroad crossing info
· Stay back 100 feet
Each of these is more important to drivers than the SCHOOL BUS sign. We know it’s a school bus; we may not be familiar with these other critical safety instructions. To complicate matters, these safety instructions have been formatted poorly. They are harder to read than they need to be because they are in sentence case. Even worse, the "Unlawful to pass" sign is not placed in proximity to the lights that will actually be flashing. The flashing lights will actually draw attention away from the signage that tells drivers what to do.
The following items are also important, and equally muted in the face of the bright SCHOOL BUS signal.
· Emergency door
· The brake and indicator lights
· The bus number, MS159
· The license plate

And, for little kids who may be walking to the bus and are unsure, I have placed the “School Bus” sign at their eye level.
When designing an interface, look for an existing signal location and build from there. The design will come together more logically and will support the task more effectively.