• listen/(watch) for approaching vehicles and see if their warning time is longer than your crossing time.
• after you've observed enough vehicles approaching, consider the range of warning times to determine if it's a Situation of Uncertainty.
  
  

• Wait till quiet/(clear), then listen/(watch) for an approaching vehicle
• Observe the warning time (detection-to-arrival time) of the vehicle
• Compare to crossing time
• Repeat till you can draw a conclusion
  

1. WAIT TILL QUIET/(CLEAR), THEN LISTEN/(WATCH) FOR AN APPROACHING VEHICLE:

While standing at the edge of the crossing, have the students who are using their vision wait until they see no vehicles approaching, and those who are using their hearing wait until it is quiet (if there is a steady noise that is considered part of the conditions of that situation, "quiet" should be when there are no temporary extraneous noises that could mask the sound of the approaching vehicles).

Examples of steady noises that are part of the situation would be the sound of an air conditioner or a fountain, or a steady noise you are creating so the student can learn about the effect of masking sounds (this will be explained in Section 4).


The students then listen or watch for traffic and report the first detection of something that MIGHT be an approaching vehicle. They should not wait until they are sure it is a vehicle before they report hearing/(seeing) something that might be coming. If they report an approaching vehicle and there are none coming, thank them and encourage them to continue doing that, rather than waiting to be sure before telling you they detected something that might be an approaching vehicle.

• If they are using their hearing, they can report when they hear a vehicle approaching in either direction.
• If they are using their vision, they can only look in one direction at a time, so they will assess each direction separately. First they watch and report their detection of vehicles in one direction until that assessment is complete, then they will turn and do the same for traffic coming from the other direction (strategies to look efficiently from one side to the other to make sure it is clear in both directions will be covered in Section 4 -- for now, you are just assessing the situation in each direction, one at a time).
  
  

2. OBSERVE THE WARNING TIME (detection-to-arrival time) OF THE VEHICLE:

Start a stopwatch when the students first suspect that they hear/(see) something that might be an approaching vehicle. While you are timing the approaching vehicle, the students should considering whether its warning time is longer than, shorter than, or about the same as their crossing time.

Stop the watch when the approaching vehicle passes in front of the student, but don't report the result until after the student guesses whether or not the warning time was longer than the crossing time.



Was it quiet when the vehicle was heard? Sometimes when assessing situations for students who use hearing, a vehicle's detection-to-arrival time is considerably less than that of other vehicles because when the student first heard it, there was extraneous masking noise (perhaps unnoticed by the student). In that case, you can't use the detection-to-arrival time of that vehicle to conclude it is a Situation of Uncertainty. However, you can take the opportunity to make students aware of the presence of a masking sound and how it can reduce their ability to hear the vehicles (this will be covered in Section 4).

3. COMPARE WARNING TIME TO CROSSING TIME:

Once the vehicle passes, ask the students if they think they would have made it across the street or lane(s) before the vehicle arrived if they had started crossing just before they heard/(saw) it. In other words, was the warning time of the approaching vehicle longer than the time they needed to cross that part of the street (the first half of the street for traffic coming in the nearest lanes, and the full street for traffic coming in the last lanes)? Let them know if they were right or not -- if they are not guessing correctly, it may be helpful to review their intuitive understanding of crossing time.

If the time recorded for a vehicle's detection-to-arrival is...
• less than the students' crossing time, then that vehicle would have reached them if they had started to cross just before they heard/(saw) it. (YIKES!)
• longer than the students' crossing time, they would have completed the crossing before that vehicle reached them, even if they had not started until just before they heard/(saw) it. (WHEW!)

4. REPEAT TILL YOU CAN DRAW A CONCLUSION

You can draw a conclusion when one of the following happens:


1. The detection-to-arrival time (warning time) of a vehicle is SHORTER than the student's crossing time even though
• you started the timer the instant the student first heard/(saw) anything that might possibly be a vehicle, and
• it was quiet/(clear) when the vehicle was first detected (no temporary sounds or blockage or glare, etc.)
  
Conclusion: The student is in a Situation of Uncertainty.


2. The full range of detection-to-arrival times for traffic coming from both directions is LONGER than the student's crossing time.
Conclusion: The student is in a Situation of Confidence.


Hey, I already know what you're asking yourself! You're saying:


It's easy to confirm I'm in a Situation of Uncertainty -- all it takes is the warning time of one vehicle that is shorter than my crossing time, even though it was quiet when I first heard it.
But to confirm that I'm in a Situation of Confidence -- how the heck can I be sure that I've measured the warning times of enough vehicles to know that the "full range of detection-to-arrival times" for traffic approaching from that direction is longer than the crossing time?


Yes, that is a HUGE issue which merits further discussion! The next few pages will address that issue.