Research -- What did we learn from sitting in lawnchairs?

If you want some good bed-time reading material to help you fall asleep at night, you can check out the full report of our research in the December 2008 Journal of Visual Impairment and Blindness (Detecting Approaching Vehicles at Streets with No Traffic Control). But that isn't necessary -- I'll tell you what we learned in a nutshell.

As you read the following results, keep in mind that the crossing time, based on the average walking speed of 4 feet/second, is almost 4 seconds for traffic from the left (which is on the first half of the street), and to get clear of traffic from the right would take 7 seconds.

Of the 6 approaches where subjects listened for vehicles:

Several approaches were Situations of Confidence.
When it was quiet at both of the "Straight" approaches (crossing time almost 4 seconds for traffic approaching from the left and 7 seconds for traffic from the right) and at the "Trees" approach (crossing time for that traffic was almost 4 seconds), the subjects heard all the vehicles at least 7 seconds away (see Table 1 below).

This means that if pedestrians with normal hearing and an average walking speed had started to cross these approaches while it was still quiet, they could be confident that no vehicle from those directions was approaching that could reach them during their crossing (heck -- if there were such a vehicle coming, they could have heard it!).
Several approaches were Situations of Uncertainty.
To no one's surprise, even when it was quiet at the "sharp bend" approach (the site that Linda Sussman had found 22 years ago and which was shown on the videotape on page 7), the AVERAGE time from when subjects heard those vehicles until they arrived was only 5.22 seconds (the range was 4 to 19 seconds).

The crossing time for the average person there is 7 seconds, which means that more than half of the vehicles could not be heard until they were so close that if a pedestrian with average walking speed had started to cross just before hearing them (when it was still quiet), the driver would have had to slow down to avoid hitting the person. The "hill" approach (crossing time 7 seconds) was another Situation of Uncertainty, because some of the vehicles could not be heard until they were less than 7 seconds away (see Table 1 below).

Table 1: Time of detection to arrival for vehicles (heard when quiet)

Condition / site

(no. of trials)

straight

(144)

Baffle

(50)

Minor bend

(39)

Severe bend

(60)

Hill

(43)

Trees

(24)

Average (in secs)

12.02

13.24

12.45

5.22

7.58

12.31

Range (in secs)

7 to 35

5 to 32

4 to 28

4 to 19

4 to 20

7 to 26

What factors affected the subjects' ability to hear the vehicles?

MOST

(click on your guess below, or if you're too tired to guess, click here to find the answer)

LEAST

(click on your guess below, or if you're too tired to guess, click here to find the answer)

It is important to note, however, that these factors altogether accounted for only a third of the variability in people's ability to hear the vehicles approaching.

That means that no single feature or even combination of features can predict that there will be a Situation of Uncertainty.

Pedestrians who are blind "need to be aware that before they can assume that it is clear to cross when quiet in a given situation, they must first observe their ability to hear the vehicles in that situation and determine whether they can hear well enough to know that it is clear to cross."

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