Section 1: Situations of Uncertainty -- Page 11 of 22        Self-Study Guide | OUTLINE | INDEX | Section 1 | Section 2 | Section 3 | Section 4 |Section 5 | REVIEW |

** The only way to determine whether you are in a Situation of Uncertainty is to
• gather data by observing the warning times of approaching vehicles detected when quiet/clear and compare those warning times to your crossing time ("warning time" is the time from when you first think you hear /see a vehicle until it arrives).
  
  
We will explain in more detail in Section 2, but basically when you've made your observation, you can determine that you are either
• in a Situation of Confidence because the shortest warning time you observed of vehicles heard when quiet / seen when clear was so much longer than your crossing time that you are confident that it is extremely unlikely that any of the vehicles approaching in that situation could get close enough to reach you without you being able to detect them,
  In this situation you can feel confident you have time to cross whenever it is quiet / clear -- if there was a vehicle close enough to reach you, you would have detected it.
  
  OR
  
  
• In a Situation of Uncertainty either because
  • even when it was quiet / clear, the warning time of at least one approaching vehicle was close to or less than your crossing time, or
  • you were unable to gather any data because you couldn't observe any approaching vehicles heard / seen when quiet / clear.
  In this situation, you don't know if you have time to cross, even when it is quiet / clear, because you can't be confident that if a vehicle was approaching that could reach you, you'd know it.
  
  
  
** But . . . but . . . aren't there other criteria that can help determine whether "cross when quiet/clear" is reliable?

No - Other than observing whether the warning times of approaching vecicles are longer than your crossing time, there are no rules or guidelines that reliably predict whether you are in a Situation of Uncertainty.     None!

Even rules that seem intuitive are not reliable! For example I once assumed that at crossings where there is nothing blocking the view of approaching vehicles, those vehicles can be heard with plenty of warning.

I was so wrong! I will illustrate this with an embarrassing story. Many years ago, I was looking for a street-crossing situation for my client to analyze, and I wanted it to be a Situation of Confidence where she could hear the approaching vehicles with plenty of warning.

I chose the crossing in the photo to the left. It seemed perfect! The road was narrow (only 2 lanes), the speed and traffic volume were low, and there was nothing blocking the sound of traffic -- I could see the traffic approaching from quite a distance.

So I brought her there for our session. As she listened to the traffic to figure out how wide the street is, she quietly said, "I can't hear the cars well enough here to know if it's clear to cross."

That session was videotaped, and I still chuckle when I see my face showing the shock and disbelief that I felt when she said that.   I thought, "This can't be true!" So I listened, and sure enough -- she was right! I could see the cars coming but neither of us could hear them until they were about 5 seconds away.