Vehicle control and drowsiness - VTI

18.4 Time to Line Crossing – TLCIn a study by Verwey and Zaidel [52] it was found that TLC is a promisingpredictor for driver impairment induced by drowsiness. TLC is defined as the timeleft until a moving vehicle crosses either side of the lane boundaries (white lines)under the assumption that the vehicle continues along the same travel path withthe current momentary motion. TLC seems to be a good cue to determine adriver’s lateral safety margins. To calculate the real TLC, road geometry data areneeded. However, in this study only lateral position data were available.Subsequently, we had to use approximations to calculate TLC. For the analysisconducted in this project it is no possible to determine the potential in using theTLC measure in this area. However, we could not find that TLC could be used ona group level to predict fatigue induced impaired driving. Furthermore, whendetecting that the driver is to close to the line it is often too late to warn the driveretc. Finally, looking at the TLC when the driver is relatively far from the laneboundaries makes the TLC calculation inaccurate.18.5 Spectral analysis of Lateral PositionThe results from the analysis of lateral position frequency conform to the resultfrom the literature study. The frequency variation was not related to the rateddrowsiness, while the amplitude of the spectral components showed association toit. We suggest that further studies should focus on modern mathematical spectralanalysis techniques, such as short time frequency transform and Wavelets.18.6 Possible measuresBelow is a table that shows a summary of measures possible to use with the givenpreferences in the previous data analysis section. Advantages and disadvantagesof the measures when used for detection of drowsiness in simulated driving aredescribed shortly.Table 10 Summary of possible measures to detect drowsy driving conditions.Measure Advantage DisadvantageLateral position and SDLP A measure that may changewith increasing drowsinessSteering movementsTLCSome steering variables arerelated to the amount ofdrowsiness (s.8–10)A measure that may changewith increasing drowsinessDifficult to see significantdifferences between tired andalert driversRoad geometry influence theresultRoad geometry may influencethe result. Difficult to calculatein real-time.The purpose was to find a method to predict when the driver is starting to drivepoorly and not to detect when the driver is drowsy. Such a method would then beused in order to investigate if a possible negative effects of a Vision EnhancementSystem on driver’s level of drowsiness. Signs of drowsiness might precedeimpaired driving behaviour. When a driver becomes drowsy is very individual.The main focus should be on how the driver handles the car and not when he istired.VTI meddelande 922A 75