Table 1.

Effects of caffeinated coffee in comparison to decaf on simulated driving performance and subjective sleepiness

	Time	Decaffeinated coffee	Caffeinated coffee
Driving test results
Standard deviation of lateral position (cm)	1	21.43 (4.37)	22.11 (3.67)
	2	23.65 (5.90)	24.13 (4.76)
	3	22.92 (4.61)	21.08 (3.74)*
	4	23.69 (4.72)	22.41 (4.37)*
Standard deviation of speed (km/h)	1	0.85 (0.44)	0.88 (0.35)
	2	0.98 (0.51)	1.1 (0.61)
	3	1.03 (0.72)	0.78 (0.34)*
	4	1.15 (0.77)	0.87 (0.56)*
Mean lateral position (cm)	1	−18.04 (12.71)	−18.03 (10.47)
	2	−19.24 (12.60)	−18.98 (9.98)
	3	−18.63 (12.31)	−20.16 (11.05)
	4	−18.17 (11.54)	−18.93 (10.80)
Mean speed (km/h)	1	95.40 (0.19)	95.42 (0.21)
	2	95.46 (0.16)	95.40 (0.26)
	3	95.44 (0.31)	95.54 (0.18)
	4	95.53 (0.15)	95.54 (0.25)
Subjective driving assessments
Driving quality	1	9.75 (3.66)	9.08 (4.10)
	2	9.01 (2.81)	8.48 (3.46)
	3	9.70 (3.89)	11.84 (2.82)*
	4	9.23 (3.02)	10.60 (3.41)
Mental effort	1	5.33 (2.30)	5.70 (2.47)
	2	5.84 (2.76)	6.39 (2.50)
	3	5.89 (2.82)	4.50 (2.36)*
	4	5.72 (2.38)	4.90 (2.93)*
Subjective sleepiness scores
Karolinska sleepiness scale	Baseline	3.25 (0.94)	3.33 (0.87)
	1	6.08 (1.67)	5.83 (2.16)
	2	6.17 (1.95)	6.29 (1.97)
	3	6.13 (2.11)	4.21 (1.47)*
	4	5.79 (1.59)	4.54 (1.86)*

Mean (SD) is shown for each parameter. Driving quality ranges from 0 (“I drove exceptionally poorly”) to 20 (“I drove exceptionally well”). For mental effort, higher scores indicate higher effort; higher KSS scores indicate increased subjective sleepiness

*p < 0.05 compared to decaf