Section 4: Teaching to determine crossable gaps --
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When you can hear/(see) traffic at a distance:
Determine when the traffic is far/slow enough to allow you time to cross:
After enough practice with feedback, students who can hear/(see) approaching vehicles from a distance can usually judge whether or not the vehicles are far and/or slow enough that they can cross (the time-to-arrival of the traffic gives them enough time to cross).
Below is the procedure I use to provide this practice and feedback.
I call the procedure "Determining Gaps in Approaching Traffic."
I used to call it "the Timing Method for Assessing the Speed and Distance of Vehicles" but too many people confused it with the TMAD.
Determining Gaps in Approaching Traffic (was "TMASD")
Procedure:
1. Define an arbitrary length of time, which we will call "X" seconds.
- If the purpose of using this procedure is for students to learn to determine when they have a gap in traffic long enough to cross, "X" seconds should be the time needed to cross as well as some clearance time (safety margin) and a second to allow for error (this is explained in more detail on the next page).
- If you simply want assess or improve students' judgment of the speed and distance of traffic, "X" seconds can be any randomly-selected time.
2. The students stand at the curb and, as a vehicle approaches, start a stopwatch when they think it's the last possible moment that they could start a crossing without making the driver have to slow down for them.
In other words, they start the stopwatch when they think that the vehicle is exactly X seconds away.
3. Stop the watch when the vehicle reaches the students.
If the lapsed time is significantly longer or shorter than X seconds, the students did not accurately perceive or judge the vehicle's speed, or distance, or both (or they don't have a good understanding of their crossing time -- see Understand Crossing Time").
Students can use this feedback to modify when they start the timer the next time.
4. Students continue to judge the vehicles as in steps 2-3, with the goal of improving their judgment until they can discern when the vehicles, regardless of their speed, are X seconds away from the students, or when the vehicles are still just far enough to allow the students time to cross.
As students become skilled, they will start the stopwatch for faster vehicles when they are further than they will for slower vehicles.
Accuracy can be expected to be within one second of the arbitrary time "X" (see note on next page).
CAUTION: If students who are using vision simply start the timer every time the nearest vehicle passes a certain landmark, they will NOT develop and improve their judgment of the speed and distance of those vehicles.
Be sure that they are starting the timer when they think that a vehicle approaching at that speed is at a distance such that it will reach them in "X" seconds (or will allow them enough time to cross).
NOTE: If a vehicle changes speed while being timed, disregard that trial, since in that situation it isn't possible to know whether the student judged its initial speed and distance accurately.
Students who use vision to cross should learn to judge when the traffic is too close/fast in a variety of lighting conditions, including at night
(it was at night that Lorraine Evensen misjudged how close and fast the traffic was coming).
Doesn't seem to be working?
If the student's judgment does not improve, perhaps he or she is unable to perceive the speed and distance of vehicles accurately because of severely restricted visual fields or impaired acuity, or is unable to cognitively process the speed and distance.
In that case, the student could consider alternatives for determining when there is enough of a gap in approaching traffic to start crossing (an alternative is explained on page 9).