Why We Fall Asleep When We Drive Steadily for a Long Time
It can be explained by cognitive and biological factors, combined to make our brain not operating at its peak performance.
Cognitive factors
Problem
It is due to the consistency in processing information.
When we can do something merely by repetition and it gives us no additional benefits to improve it, we no longer think about it and do it unconsciously to save energy.
Consequences
With a low brain activity it is easy to fall asleep and becomes unable to notice road situation.
Solution
To solve this problem, some governments are making roads more complex to keep drivers alert to the road situation.
A common way is do that is adding road curves when the shortest way to travel is a straight road, so that the problem of highway hypnosis can be prevented.
Biological factors
Problem
A potential biological cause for that is accumulation of carbon dioxide inside the car, since air may be trapped and circulated there with limited ventilation.
Our breathing rate is determined by the carbon dioxide level, which acts as an indicator of oxygen level.
Since oxygen are constantly being consumed by our body, its level cannot be accurately measured.
On the other hand, the carbon dioxide level in our body reflects the oxygen level more accurately.
In respiration, the ratio of oxygen consumed and carbon dioxide produced is 1:1, so the increase in carbon dioxide level perfectly indicates the decrease in oxygen level.
Moreover, carbon dioxide is not consumed by our body, so its level can be measured more accurately.
Consequences
So the accumulation of carbon dioxide inside leads to an increase of carbon dioxide level in our body, triggering us to breath faster to obtain more oxygen.
However, as no fresh air comes in, faster breathing still does not give us enough oxygen, so the process goes on and potentially causes breathing problems.
Thus, we are saving oxygen instead.
Body activities that are not essential may not function at its maximum performance, as oxygen is saved for essential life activities.
One symptom is feeling sleepy, as our brain does not operate fully.
Solution
A quick fix is allowing exchange of air with outside, which removes excess carbon dioxide and brings in sufficient oxygen, but it also means allowing air with poor quality to flow inside the car.
An alternative is having green plants inside the car, which produce oxygen in the sunlight by photosynthesis, but it would not work if the outside is dark as the plants consume oxygen instead.
