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Timing Method for Assessing Detection of Vehicles (TMAD)

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A checklist is available for the TMAD


The last page told you to use the Timing Method for Assessing the Detection of Vehicles (TMAD) to thoroughly assess crossing situations when following the "Procedure to Develop Judgment of the Detection of Traffic."

The TMAD analyzes whether the student can hear/(see) the vehicles with enough warning in that situation to know when it's clear to cross. This analysis gives students feedback as to whether they were correct with their initial judgment that it was a Situation of Uncertainty or of Confidence. The TMAD can also be used to help students understand the effect of masking sounds, which will be explained in Section 4.

** The TMAD is not intended for use by students!

Travelers should be able to recognize Situations of Uncertainty after briefly observing the traffic whenever planning to cross streets (including familiar ones). The TMAD assessment often takes 30 minutes or more to complete, so it isn't practical for use while traveling -- it is intended only as a tool to teach students to recognize Situations of Uncertainty.


** The TMAD cannot assess crossings, it can only assess situations (see considerations below).


TMAD Procedure


• Determine crossing time
• Wait till quiet/(clear), then listen/(watch) for approaching vehicles
• Time the detection-to-arrival of a vehicle
• Compare to crossing time
• Repeat till you can draw a conclusion
  
  
1. DETERMINE CROSSING TIME:


If this is for assessing a crossing with two-way traffic, you will need two measurements:
• 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).
  
  
You can determine the time needed for the crossing by timing several crossings of the street (or an equivalent length) and use the longest time (if you want to read an example of using an equivalent length measured in a parking lot, click here).

To time the crossing:

Start the timer when the student is committed to the crossing.

• 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 when the student steps out of danger for that traffic.

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


While standing at the edge of the crossing, have the students wait until they can hear/(see) no 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.
  
  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 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 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).
  
  
  
3. TIME THE DETECTION-TO-ARRIVAL OF A VEHICLE:


Start a stopwatch when the students first suspect that they hear/(see) something that might be an approaching vehicle.

Stop the watch when the approaching vehicle passes in front of the student.

If students report an approaching vehicle and there are none coming, praise them for reporting something suspicious, and reset the watch to wait for a vehicle.


4. COMPARE:


Compare the vehicle's detection-to-arrival time with the time the student needs to cross.

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!)
  


5. REPEAT TILL YOU CAN DRAW A CONCLUSION


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


1. a vehicle reaches the student in less time than he needs to cross 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 (or the conditions were as good as they can be in that situation, such as no extraneous masking sounds, no temporary glare, etc.)
  
  Conclusion The student is in a Situation of Uncertainty.
  
  
2. the shortest detection-to-arrival time is longer than the student's crossing time even after

• you have measured the full range of detection-to-arrival times of vehicles in that situation.
  
  Conclusion: The student is in a Situation of Confidence.
  
     Hey, I already know what you're asking yourself!
  
  How the heck can I be sure that I've "measured the full range of detection times of vehicles in that situation"?
  
     Yes, that is a HUGE issue which merits several pages to discuss! The next page will start to address that issue.
  
  
Considerations 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 there were no extraneous masking sounds when the student reported hearing the vehicles. If there are constantly extraneous sounds and never any quiet, you will not be able to use that site to teach the student to recognize Situations of Uncertainty (page 9 will explain how to select good sites/situations to use the "Procedure to Develop Judgment of the Detection of Traffic").
  
  
• Can you analyze crossings? Or only situations?
  
  ** It is important to remember that the conclusion you make about a situation is true only under those conditions of the situation that was assessed. You can analyze situations, but you cannot make any conclusions about crossings. For example if the crossing is analyzed while the road is wet, the conclusion may not be the same as it would be when it is dry, or when the residual noise level is louder, or when a parked truck blocks the sound of traffic.
  
  At the crossing where Gordon Parks was killed, for example, analysis with the TMAD showed that the crossing was a Situation of Uncertainty at 4:00 Friday afternoon, but not at 8:00 the next night. Saturday night, it was possible to hear the vehicles much further, perhaps because the sound level of "quiet" was lower then.
  


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