This is what we've been preparing the students for - we're almost there! The whole point of all this preparation is for your students to be able to observe a few vehicles and determine if they can be confident that they have time to cross whenever it's quiet/(clear).
To be confident that, as they start to cross, there is no vehicle close enough to be able to reach them during their crossing, they need to know that the warning time of any vehicle that approaches IN THAT SITUATION will be at least as long as their crossing time. "Warning time" is the time from when the vehicle is detected until it arrives. For example, if your crossing time is 7 seconds, you want to be able to detect the vehicles before they get within 7 seconds of reaching you. If you can't do that, you might start to cross when there is a vehicle coming that could reach you and would have to slow down in order to avoid hitting you.
In other words, in order for you to be confident that you have time to cross whenever it's quiet/(clear), you need to be confident that in that situation, the warning times of all approaching vehicles that are heard when it's quiet/(seen when it's clear) will be longer than your crossing time.
So how does this process for assessing crossing situations work?
Basically, you teach your students to . . .
- listen/(watch) for approaching vehicles HEARD WHEN QUIET / (SEEN WHEN CLEAR) and compare the warning time of each vehicle to their crossing time.
- after they've observed enough approaching vehicles, they consider whether they can be confident that when it is quiet/(clear), it is extremely unlikely that approaching vehicles can get close enough to reach them without their being able to hear/(see) the vehicle.
Here's the process (described below):
- Wait till quiet/(clear), then listen/(watch) for an approaching vehicle
- Observe the warning time (detection-to-arrival time) of the vehicle
- Compare its warning time to crossing time
- Continue collecting data till you can conclude whether it is extremely unlikely that there will be any approaching vehicles that can get close enough to reach you without you being able to detect it.
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).
- 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).
- 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).
2. OBSERVE THE WARNING TIME (detection-to-arrival time) OF THE VEHICLE:
- The instructor will . . .
. . . 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 be 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.
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 as a data point to conclude whether 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 ITS WARNING TIME TO CROSSING TIME:
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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?
for traffic coming in the nearest lanes, the crossing time would be the time needed to cross the first half of the street (in other words, to get out of the path of those vehicles),
and for traffic coming in the last lanes, the crossing time is what they need to cross the whole street.
- 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!)
If they say that they would have had time to cross before it arrived, ask if it was a close call or if they would have had much more than enough time.
Then let them know if they were right or not. If not, it may be helpful to review their intuitive understanding of crossing time.
If the time recorded for a vehicle's detection-to-arrival is...
4. CONTINUE COLLECTING DATA TILL YOU CAN DRAW A CONCLUSION
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You can draw a conclusion when one of the following happens:
- 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.)
- 1. The detection-to-arrival time (warning time) of a vehicle is SHORTER than the student's crossing time even though
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Conclusion: The student is in a Situation of Confidence.