Influence of optic flow field restrictions and fog on perception of speed in a virtual driving environment

Traffic Simulation and Visual Verification in Smog

Smog causes low visibility on the road and it can impact the safety of traffic. Modeling traffic in smog will have a significant impact on realistic traffic simulations. Most existing traffic models assume that drivers have optimal vision in the simulations, making these simulations are not suitable for modeling smog weather conditions. In this article, we introduce the Smog Full Velocity Difference Model (SMOG-FVDM) for a realistic simulation of traffic in smog weather conditions. In this model, we present a stadia model for drivers in smog conditions. We introduce it into a car-following traffic model using both psychological force and body force concepts, and then we introduce the SMOG-FVDM. Considering that there are lots of parameters in the SMOG-FVDM, we design a visual verification system based on SMOG-FVDM to arrive at an adequate solution which can show visual simulation results under different road scenarios and different degrees of smog by reconciling the parameters. Experimental results show that our model can give a realistic and efficient traffic simulation of smog weather conditions.

Robust Underestimation of Speed During Driving: A Field Study

Traffic reports consistently identify speeding as a substantial source of accidents. Adequate driving speeds require reliable speed estimation; however, there is still a lack of understanding how speed perception is biased during driving. Therefore, we ran three experiments measuring speed estimation under controlled driving and lighting conditions. In the first experiment, participants had to produce target speeds as drivers or had to judge driven speed as passengers. Measurements were performed at daylight and at night. In the second experiment, participants were required to produce target speeds at dusk, under rapidly changing lighting conditions. In the third experiment, we let two cars approach and pass each other. Drivers were instructed to produce target speeds as well as to judge the speed of the oncoming vehicle. Here measurements were performed at daylight and at night, with full or dipped headlights. We found that passengers underestimated driven speed by about 20% and drivers went over the instructed speed by roughly the same amount. Interestingly, the underestimation of speed extended to oncoming cars. All of these effects were independent of lighting conditions. The consistent underestimation of speed could lead to potentially fatal situations where drivers go faster than intended and judge oncoming traffic to approach slower than it actually is.

Speed choice and driving performance in simulated foggy conditions

Driving in fog is a potentially dangerous activity that has been investigated in a number of different ways; however, most have focused on identifying the underlying perceptual changes that result in an inability to perceive speed of vehicle motion. Although the previous research has identified the perceptual changes associated with driving in fog and shows that people are highly likely to perceive their speed to be higher than it actually is, these research studies have not investigated driving behavior when drivers are allowed to maintain speed as they feel appropriate and make use of the vehicle's speedometer. In addition, much of the existing research focuses on speed perception and presents a limited view of other driving performance metrics in terms of lane keeping and event detection. The current study addresses these issues utilizing a driving simulator-based method where fog is simulated as a distance dependent contrast reduction while having participants drive at speeds they feel are appropriate. A number of different instructions and speed feedback mechanisms were tested in order to determine how drivers react when driving in varying levels of fog. Results also include lane keeping measures in order to assess whether drivers are willing to drive at speeds where their lane keeping performance is degraded due to the reduced visibility. Results indicate that, in general, drivers do not tend to slow down significantly until visibility distance is drastically reduced by fog; however, lane keeping ability is maintained throughout most of the range of visibility distances. Lane keeping ability was reduced only when fog results in visibility distances <30 m. Overall, the current study shows that drivers are willing and able to maintain vehicular control at high speed when driving in fog; however, it is important to note that drivers chose to drive at speeds where they would be incapable of stopping to avoid obstacles in the roadway even if they were to identify and react to the obstacle immediately at the border of visibility distance. This research suggests that safety benefits may be gained by convincing drivers to slow down more than they would on their own when driving in fog or enhancing a vehicle's ability to identify and react to hazards that are not visible to the driver. In order to further understand the effects of driving in fog, future naturalistic driving research should focus on identifying and mitigating risky behaviors associated with driving in foggy conditions.

Effects of Reduced Contrast on the Perception and Control of Speed When Driving

Misperception of speed under low-contrast conditions has been identified as a possible contributor to motor vehicle crashes in fog. To test this hypothesis, we investigated the effects of reduced contrast on drivers' perception and control of speed while driving under real-world conditions. Fourteen participants drove around a 2.85 km closed road course under three visual conditions: clear view and with two levels of reduced contrast created by diffusing filters on the windscreen and side windows. Three dependent measures were obtained, without view of the speedometer, on separate laps around the road course: verbal estimates of speed; adjustment of speed to instructed levels (25 to 70 km h−1); and estimation of minimum stopping distance. The results showed that drivers traveled more slowly under low-contrast conditions. Reduced contrast had little or no effect on either verbal judgments of speed or estimates of minimum stopping distance. Speed adjustments were significantly slower under low-contrast than clear conditions, indicating that, contrary to studies of object motion, drivers perceived themselves to be traveling faster under conditions of reduced contrast. Under real-world driving conditions, drivers' ability to perceive and control their speed was not adversely affected by large variations in the contrast of their surroundings. These findings suggest that perceptions of self-motion and object motion involve neural processes that are differentially affected by variations in stimulus contrast as encountered in fog.