Micro Stressors in Routine Driving Identified

Every day, commuters around the world wish for optimal driving conditions, but they rarely receive them. Traffic is frequently congested, and it worsens when the weather turns bad. Light traffic and pleasant weather are commonly regarded as elements that contribute to a stress-free commute. Unfortunately, researchers from the University of Houston and the Texas A&M Transportation Institute discovered that even under such ideal settings, daily driving results in micro stressors for many people, for mysterious reasons.

Researchers report in the journal IEEE Transactions on Affective Computing that persons who are prone to anxiety had a considerably greater heart rate when driving than those who are not inclined to anxiety. Under identical conditions, nervous drivers had a heart rate that was around five beats per minute greater than non-anxious drivers.

The researchers also discovered that when the car speed increased, so did the drivers’ pulse rate. Under comparable conditions, drivers traveling at 65 mph had a heart rate four beats per minute greater than cars traveling at 25 mph. The observed cardiovascular activation was connected to sympathetic activation, i.e. stress reactions, in both cases.

“These are substantial numbers that we would have never guessed,” said Ioannis Pavlidis, Eckhard-Pfeiffer Distinguished Professor of Computer Science, who led the University of Houston group. “Anxious people who commute at highway speeds experience, on average, heart rate elevation of nine beats per minute; this is every day for an hour or more, which is the typical commuting time in this country. It is an unexpected micro stressors that is hard to ignore because of its substantial effect and its repetitive nature.”

Both Mike Manser, senior research scientist, and Robert Wunderlich, director of the Texas A&M group’s Center for Transportation Safety, highlighted that the claimed stress effect was assessed in good weather and light traffic, i.e. ideal commuting conditions. “This significant stress effect is likely to grow even larger as conditions worsen,” they warned.

The researchers used a new affective computing paradigm called NUBI, which stands for Naturalistic and UBIquitous. According to the researchers, they recruited volunteers from Texas, where most people commute everyday, the weather is usually nice, and traffic conditions in mid-sized cities are optimal. The participants were all young (the average age was 27), healthy, and experienced drivers.

Monitoring was entirely undetectable. For a week, the drivers’ heart rates were measured every few seconds using their personal Apple Watches, while their driving data was recorded via OBD II sensors, which are popular with vehicle insurance tracking programs. When they weren’t driving, the volunteers had to complete daily psychometric questionnaires through text message.

Based on the GPS signal of the drivers, we gathered momentary weather and surrounding traffic data, as well as heart rate data, from free internet sources. The individuals were also evaluated during their non-driving hours to determine the uniqueness of any driving effects.

“Across the state, we were shadowing the participants’ real-lives moment by moment for a week,” Pavlidis said. “This is the beauty of a NUBI driving study—you can monitor participants hundreds of miles away and get insights into their natural driving and non-driving behaviors.”

The final data set was massive, with 77 hours of driving and 915 hours of non-driving observations totaling approximately four million rows of multimodal information that was evaluated using machine learning and statistical models.

The findings of this study are consistent with the findings of a prior study conducted by the same researchers, which found that certain persons experience high stress even in minor acceleration events such as stop-and-go traffic. It appears that there are segments of the population for whom even minor driving is stressful. Because NUBI-style research with unparalleled access to drivers’ internal and exterior states were not practicable until recently, these everyday micro stressors were unknown or suspected.

“Because driving is ingrained into people’s lives, even individuals who exhibit the said stress responses are not consciously aware of them. Nevertheless, the responses are there, they are substantial and their long-term implications are unknown,” said Pavlidis.

In the near term, these micro stressors appear to overwhelm the drivers who experience them, because affected drivers regularly report being more exhausted than non-afflicted drivers on similar itineraries, he added. The study’s long- and short-term findings have potential lifestyle, safety, and insurance consequences, according to the researchers.

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