The exact determination of subjective risk and comfort thresholds in car following

Abstract

In this study the location of vehicle to vehicle distance thresholds for self-reported subjective risk and comfort was researched. Participants were presented with ascending and descending time headway sequences in a driving simulator. This so called method of limits of ascending and descending stimuli (Gouy, Diels, Reed, Stevens, & Burnett, 2012) was refined to efficiently determine individual thresholds for stable time headways with a granularity of 0.1 seconds. Time headway thresholds were researched for 50, 100, and 150 km/h in a city, rural, and highway setting. Furthermore, thresholds for self-driving (level 0 automation: NHTSA, 2013) were compared with thresholds for the experience of subjective risk and comfort in assisted driving, similar to adaptive cruise control (level 1 automation). Results show that preferred individual time headways vary between subjects. Within subjects however, time headway thresholds do not significantly differ for different speeds. Furthermore we found that there was no significant difference between time headways of self-driving and distanceassisted driving. The relevance of these findings for the development of adaptive cruise control systems, autonomous driving and driver behavior modelling is discussed.

Comparison of Car-Following Behavior in Terms of Safety Indicators Between China and Sweden

“…Time gap shows almost no correlation with the host vehicle speed. This is analogous to the results in [38][39][40], that is, distance headway increases as the host vehicle speed increases and time headway is nearly constant in different speed ranges. However, time headway is described to decrease as the host vehicle speed increases in [22], [41,42].…”

How speed and visibility influence preferred headway distances in highly automated driving

“…A large number of studies have found that drivers follow other vehicles with a constant time headway at different speeds, and prefer constant time headway following to non-constant following when presented with a number of time headways at different speeds (Ayres, Li, Schleuning, & Young, 2001;Siebert et al, 2014Siebert et al, , 2017Taieb-Maimon & Shinar, 2001;Van Winsum & Heino, 1996). Siebert et al (2014Siebert et al ( , 2017 researched car following preferences for the use of adaptive cruise control and found stable individual time headway preferences. Most preferred headways in self-and assisted-driving are found in the range of one to two seconds in simulated as well as in real-life driving, although preferred time headways of individual drivers differ.…”

“…Most preferred headways in self-and assisted-driving are found in the range of one to two seconds in simulated as well as in real-life driving, although preferred time headways of individual drivers differ. In all earlier studies on the relation between the subjective experience of drivers and time headway, drivers either had complete control over the vehicle (Ayres et al, 2001;Taieb-Maimon & Shinar, 2001;Van Winsum & Heino, 1996), or were actively controlling the steering wheel in studies where an adaptive cruise control system was implemented (Siebert et al, 2014(Siebert et al, , 2017. It is therefore unclear how the complete absence of active control over the vehicle in highly automated driving influences the subjective experience of time headways.…”

“…1.0 vs. 1.25 vs. 1.5 vs. 1.75 vs. 2.0 vs. 2.5 vs. 3.0 vs. 3.5 vs. 4.0). Two extra time headway increments (1.25 and 1.75 seconds) were added to more finely represent typical time headways found in earlier studies (Siebert et al, 2014(Siebert et al, , 2017. The resulting 90 experimental conditions were grouped in 9 blocks, each block consisting of a randomized order of ten time headways for the same visibility and speed.…”

“…Past research suggests that time headway is a variable held constant by individual drivers in self-driving (Siebert, Oehl, & Pfister, 2014;Siebert, Oehl, Bersch, & Pfister, 2017;Van Winsum & Heino, 1996), and the individual choice of time headway has been related to the drivers' awareness of risk and comfort (Lewis-Evans, De Waard, & Brookhuis, 2010).…”