Tuesday, April 19, 2022
April is National Distracted Driving Awareness Month. Throughout the month, Marc Gentzler, professor, psychology, will share his expertise on driver safety discovered through years of research. Marc, a professor at Valencia since 2013, obtained his doctoral degree in human factors psychology in 2014 from the University of Central Florida, with a focus on the neuroscientific aspects involved in driving. His dissertation was titled “Driving performance adaptation through practice with and without distracters in a simulated environment.” He has 14 peer-reviewed publications, 15 conference presentations and 14 conference poster presentations. Further, Marc reviews papers in his field and has previously done consulting analyzing the perceptual and cognitive factors involved in real car accident cases.
By Marc Gentzler, Professor Psychology
In my third article in this series, we will talk about nighttime visibility. There are more accidents at night, and some of the main reasons are less visibility, glare and fewer depth cues.
Let’s start with how headlights work. Low beams are typically used when it is raining and in dim/dark illuminations. The low beams actually point downward and to the right slightly to reduce glare to oncoming drivers. With this configuration, however, you are more likely to miss something on your left side since you have less light in that direction.
Especially as a pedestrian or bicyclist with no lights at night, be extra cautious when crossing in front of a vehicle on their left. If there is no opposing traffic or traffic close in front of you, no streetlights (or poor lighting) and clear conditions (no dense fog), it is best to use the high beams. Anecdotally, I rarely see cars use their high beams in these conditions.
Bikes, motorcycles and pedestrians are obviously smaller than vehicles and thus are harder to see at day and night. Therefore, light emanating from these road objects and/or reflective gear can help their detection in any lighting condition.
Many think that lights on bicycles, for instance, are only useful for dim/dark illuminations, but in fact can help detection during the day as well. You might notice most motorcycles on the road today have their headlights on during the day, much like cars have daytime running lights (DRLs). I would recommend bicycles have their lights on during the day as well. Modulating (flashing) lights can aid in detection. Overall though, I would argue that bicycle lighting could be improved.
I would follow this rule: always assume that you are not visible, especially if you are one of the above mentioned three road users. Many pedestrians assume that at night, if the vehicle’s headlights are shining on them and/or they are in front of the vehicle, they will be perceived by the driver. But again, as mentioned in my second article, sensation and perception are two different processes. You may be walking in front of the vehicle, but for any number of reasons, the driver does not perceive you. Even with just sensation, pedestrians are harder to see than one might think.
Many drivers also assume that if their headlights are on an object, then the object must be visible. But this is not necessarily the case. An important variable is contrast with the background. Even if the headlights are shining on a pedestrian, if the contrast between the pedestrian and background is not great enough, then they won’t be visible.
At nighttime, your eyes take time to become more sensitive to the dark. In fact, it might take up to half an hour to become fully dark adapted, and even longer as we age. Dark adaptation is the process of the photoreceptors (which capture light) in the back of the eye to become more sensitive to light.
When you turn off the lights in your room at night to go to bed, at first you can’t really see anything. But after some time, if you open your eyes or wake up in the middle of the night, you should find that you can see more details.
So how does this all relate to driving? The time when you need the most caution is when you start your drive at night. Your eyes are not dark adapted yet and are less sensitive to light, thus objects will be less visible. Unfortunately, the dark adaptation process can be reset somewhat with streetlights and especially with oncoming car headlights if they are close to you. The glare from the oncoming car at first is blinding, but after the car passes you, you lose some light sensitivity.
Further, if your eyes are dark adapted and you encounter oncoming headlights, it is a bit painful, more so than if you were not dark adapted. It is like when you are in the dark for a while and then suddenly the lights in the room turn on.
There is a problem with many dump trucks at night. Several of them have two small tail lights that are not placed at the width of the truck, but instead are placed close together (see image below).
Why is that a problem? There is a monocular (one eye) depth cue I mentioned in the previous article called linear perspective, where objects at a distance get scrunched together. Think of a railroad track in a distance where the rails appear to converge.
So how does this relate back to the tail lights on the truck? If a vehicle is further away, its tail lights will look closer together due to linear perspective. If a truck has its tail lights close together, it will create the illusion that the truck is further away than it actually is.
If the driver thinks the truck is further away than it really is, they might rear-end them, not realizing how close it is until it is too late (keep in mind these trucks can be going significantly slower than other traffic as well). Some of these trucks do have lights on the top which are placed at the width of the truck; however, they are typically not as conspicuous and not where the driver is focused.
Let’s discuss an important issue with daytime visibility. Visual angle is the size an object takes up in the back of the eye. The smaller the object, say a pedestrian versus a car, the less room it will take up, assuming equivalent distance.
But what we know about another monocular depth cue is that if the object is further away, it subtends less of a visual angle and therefore looks smaller. If a semitruck looks small, you correctly assume that it is further away and that it did not shrink.
But there is a problem with this. Assume that a car is coming toward you and will eventually cross your path. You may not be able to see it because it is covered by one of the front pillars in your car.
How can a big car get blocked by the small pillar? Because it is far enough away. Maybe you have a hangtag for parking. It says on it (or it should) not to drive with the hangtag. The reason is that it can block even a huge vehicle that is in a distance.
Can automation in cars help prevent some of the accidents caused by expectation violations discussed in the second article and visibility issues discussed in this article? Should we have fully automated vehicles? That will be the topic in my final article.