TIMING METHOD FOR

ASSESSING SPEED AND DISTANCE OF VEHICLES (TMASD)

Answers the question:

"Can I determine the speed and distance of approaching vehicles well enough to know

when they are sufficiently far or slow that it's clear enough to cross?"

Procedure:

1. Define an arbitrary length of time, which we will call "X" seconds. If the purpose of this procedure is for you to learn to judge when you have a gap long enough to cross, “X” seconds should be the time needed to cross, including some clearance time (see note below). If you simply want to improve your judgment of the speed and distance of traffic, “X” seconds can be any randomly-selected time.

2. Stand at the curb and, as a vehicle or vehicles approach, try to judge (based on their speed and distance) when you feel that you could still start a crossing and reach the other side with sufficient clearance time before the first vehicle reaches you (or try to judge when a given vehicle is X seconds away). Start a stopwatch when you think it’s the last possible moment that you could safely start a crossing (or when you think that a given vehicle will reach you in exactly X seconds).

3. Stop the watch when the vehicle reaches you. If the lapsed time is significantly longer or shorter than X seconds, you did not accurately perceive or judge the vehicle's speed, or distance, or both (or you don’t have a good understanding of your crossing time – see Program to Teach Concepts and Risk Analysis for Uncontrolled Crossings).

Use this feedback to modify when you start the timer the next time.

NOTE: If a vehicle changes speed while being timed, disregard that trial, since in that situation it isn't possible to know whether you judged its initial speed and distance accurately.

4. Continue to judge the vehicles as in steps 2‑3, with the goal of improving your judgment until you can discern when the vehicles, regardless of their speed, are approximately X seconds away from you (that is, you will start the stopwatch for faster vehicles when they are further from you than you will for slower vehicles). [Accuracy can be expected to be within one second of the arbitrary time "X" ‑‑ see note below.]

Many people will simply start the timer every time the nearest vehicle passes a certain landmark. Although this is an effective alternative strategy that can be used by people who cannot develop the ability to judge the speed and distance of vehicles, doing it during this training will not enable the development of an accurate judgment of the speed and distance of vehicles because it does not provide any feedback about that judgment.

If your judgment does not improve, perhaps you are unable to perceive the speed and distance of vehicles accurately because of impaired depth perception or acuity or you’re unable to cognitively process the speed and distance, and you should consider alternatives to determine when there is enough of a gap in approaching traffic to start crossing. One such alternative is to choose a landmark (such as a driveway, or pole, or tree) at a distance such that even the fastest vehicles take more time to reach you from that spot than you need to cross.

How to determine how many seconds is “X” seconds?

When developing judgment of gaps for crossing, “X seconds” is typically the time needed to cross either the whole street (for analyzing traffic from the right), or half the street (for analyzing traffic from the left), plus a safety margin (“clearance time”), plus an extra second to allow for error.

The one-second error margin is needed because most people can learn to make this judgment accurately within one second or less. That is, they can determine when the vehicle is X seconds away, give or take one second or less.

The safety margin / clearance time is the time from when you complete the crossing until the first vehicle passes your crosswalk. The preferred clearance time will vary, depending on the situation and the person. People may want more clearance time for fast-moving traffic than they do for slow traffic, and cautious people may want a longer clearance time than do high risk-takers.

The crossing time, preferred clearance time, and error margin should all be considered when determining how many seconds "X" will be. For example, if you need 6 seconds to cross and want a safety margin / clearance time of 3 seconds, you want to be sure the traffic is at least 9 seconds away when you start to cross. Thus your "X" should be 10 seconds, so that if you misjudge a car by one second, you'd still have the full 9 seconds of clearance that you want.

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