to determine there is a crossable gap in approaching traffic
ALTERNATIVE when you cannot judge whether the traffic is far/slow enough to allow you time to cross:
I have had about a half-dozen students who were able to see the vehicles at a distance but were unable to judge their speed and distance.
There is an alternative that they were each able to use for judging whether they have enough time to cross when they see vehicles approaching.
This alternative is to choose a landmark (such as a driveway, or pole, or tree) at a distance such that, from that spot, even the fastest vehicles take more time to reach them than they need to cross.
The warning times of approaching vehicles can be measured to help determine if the landmark is far enough.
If it is, then you can be confident there is enough time to cross if there are no vehicles closer to you than that landmark.
This is an alternative strategy for those who are not able to judge the speed and distance of the vehicles.
While students are still trying to learn to judge the speed and distance of the vehicles, do not suggest that they start the timer whenever the vehicle passes a certain landmark, as this will impede their learning to judge the gaps in traffic.
In my experience, people who do not have binocular vision (for example, have only one functioning eye) have done very well with judging the speed and distance of the vehicles.
Those who cannot do it are more likely to be people with very small visual fields than people with monocular vision.
Perhaps this is because, for judging speed and distance of an approaching vehicle, even more important than binocular vision is the ability to see what is around that vehicle, such as the trees, bushes, and poles that it is passing.