Vehicle control and drowsiness - VTI

109Tiredness876Predicted YTiredAlert5430,1 0,2 0,3 0,4 0,5 0,6 0,7mean SDLPFigure 28 Regression plot for both alert and tired drivers without the extremesubjects.Conclusion:There is a relationship between increasing drowsiness, as measures by the KSSmethod, and increasing SDLP for both the group of tired drivers and the group ofalert drivers. The variation in SDLP for the group of tired drivers is smaller whenthe two extreme subjects are eliminated from the data. The drowsiness rating forthe tired drivers starts and ends at higher levels than for the alert drivers (seefigure 20).With the SAVE data from VTI, it was possible to make a similar regressionanalysis of the alertness versus the SDLP. However, in the SAVE study; only thetest leader rated the drowsiness of the subjects during the drive on a six-gradedscale. The subjects did not rate their own drowsiness while driving as in the”Hök” study. The analysis showed that there is a possible relationship betweendecreasing alertness and increasing SDLP. But the results had a low correlation(R=0.7). Probably because half of the driving sessions in the SAVE experimentdata were incomplete. Because of the incomplete data sets no conclusions can bedrawn, except that there are tendencies towards the same results as the analysismade on the data from the ”Hök” study a relationship between increasingdrowsiness and increasing SDLP.VTI meddelande 922A 57