Procedure to Develop Judgment of the Detection of Traffic

NOTE:

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Timing Method for Assessing Detection of Vehicles (TMAD)

TMAD Procedure

TMAD Checklist

3 photos show a boy with a white cane stepping off a curb, walking across the street and reaching the other side of the street -- his cane has crossed the white line at the edge of the street's shoulder.

DETERMINE CROSSING TIME AND

DEVELOP INTUITIVE UNDERSTANDING OF CROSSING TIME:

the time to cross the first part of the street (for traffic coming from the left) and
the time to cross the entire street (for traffic coming from the right).

longest time

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To time the crossing:

Start the timer

Normally this means when the student starts to move into the street but in some instances, once students commit to the crossing they have to do something before stepping into the street. For example some students may be committed to crossing once they
- determine that it is clear to cross using a monocular (crossing time includes time to put down the monocular and get the cane ready); or
- give a command for their guide dog to move forward (crossing time includes time for the dog to start crossing).
For students using vision, the crossing time for traffic from the right might have to include time to look for traffic from the left (teaching students to look for traffic right and left effectively is covered in Section 4).

Stop the timer

For traffic from the left, this means when the student has stepped out of all lanes that can be used by that traffic, including turning lanes.
For traffic from the right, you and your students will need to determine where they are out of danger. For example, in some situations they may be out of danger when they reach the parking lanes or the shoulder of the street, in other situations they are not out of danger until they cross those also.

Develop intuitive understanding of crossing time

intuitive understanding

WAIT TILL QUIET/(CLEAR), THEN LISTEN/(WATCH) FOR APPROACHING VEHICLES:

If they are using hearing, this should be when it is quiet or, if there is a steady noise that is considered part of the conditions of that situation, this should be when there are no extraneous noises that could mask the sound of the approaching vehicles.

first detection

MIGHT

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 glance 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).

photo shows the boy with a white cane in one hand and a stopwatch in the other. He is standing at the curb of a street that has a bend to the right. He is looking at a truck that has just come around the bend on the right.

photo shows the truck passing in front of the boy and he is looking at his stopwatch.

TIME THE DETECTION-TO-ARRIVAL ("warning time") OF A VEHICLE:

Start

might

Stop

COMPARE TO 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!)
more than the students' crossing time, they would have completed the crossing before that vehicle reached them, even if they had started just before they heard/(saw) it. (WHEW!)

REPEAT TILL YOU CAN DRAW A CONCLUSION

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:

Situation of Uncertainty

The full range of detection-to-arrival times for traffic coming from both directions is LONGER than the student's crossing time.

Conclusion:

Situation of Confidence

How the heck can I be sure that I've measured the warning time of enough vehicles to know that the "full range of detection-to-arrival times" for traffic approaching from either direction is longer than the crossing time?

Consideration when using the TMAD:

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 less than the crossing time because when they 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).

To find out if they can hear the traffic well enough whenever it is quiet, continue steps 2-4 while making sure that when the student reported hearing the vehicles, there were no extraneous masking sounds.

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