Standard operation procedures for conducting the on-the-road driving test, and measurement of the standard deviation of lateral position (SDLP)

Figures & data

Figure 1 The standard deviation of lateral position (SDLP).

Figure 2 One of the instrumented cars of Utrecht University.

Figure 3 Schematic representation of the on-the-road driving test.

Figure 4 Examples of lateral position and speed changes over distance traveled. Adapted with permisison from Volkerts ER, de Vries G, Meijer T, et al. Driving performance the day after use of loprazolam, flunitrazepam and placebo. VSC, Report VK 83-04, Traffic Research Centre, Groningen, The Netherlands, 1984.¹¹

Figure 5 Standard operation procedures to edit the raw data of the driving test. The top figure shows the mean lateral position (MLP) of the car. The bottom figure shows the mean speed (MS) of the car. Standard operation procedures: A) Start of the test: data is deleted until the subject drives 95 km/h in gear number 5. B) An overtaking maneuver: data is deleted from the start of accelerating to overtake, or moving to the left lane, until the car is returned completely back on the right lane and its speed is returned to 95 km/hour. C) Attempt to overtake: data is deleted from the first attempt to overtake. D) Between two overtaking maneuvers: data is deleted when the distance between the two maneuvers is at less than 600 meters. E) Out of the detection range: data is deleted. F) Collisions, off road crashes, other events requiring stopping or slowing speed: data is deleted from the moment of the crash until the car drives 95 km/hour in gear number 5. Cut-off points for editing are indicated by |.

Figure 6 SDLP values obtained after administration of placebo.

Data from references ², ^12–24.

Figure 7 Test–retest reliability of SDLP measurement.

Data from n = 98 healthy volunteers (data from references ², ^12–18).

Note: Driving tests were performed in the morning or afternoon following bedtime administration of placebo (9–10 hours and 16–17 hours after intake).

Figure 8 SDLP values and weather conditions.

Data from 174 driving tests of healthy volunteers who received placebo treatment (Data from references ^21–23, ²⁵).

Table 1 Data from one driving test, when using different length of segments

100 km	Segment	10 × 10 km	20 × 5 km		50 × 2 km
15.3	0–10 km	12.1	12.5	12	No data	No data	10.7	13.9	5.3
	11–20 km	13.2	10.5	12.8	8.1	11	8.3	13	13
	21–30 km	11.6	12.6	8.9	11.4	11.3	8.7	10	9.4
	31–40 km	17.7	10	12.5	7.8	11.8	12.8	8.5	12.7
	41–50 km	15.4	16.4	13.4	13.8	9.8	15.8	9.5	11.1
	51.60 km	10.3	9.9	9.4	9.4	8.4	9.1	8.1	8.4
	61–70 km	15.5	19.3	10	10.1	23.1	11	8	10
	71–80 km	13.9	13.7	13.9	12.1	15.1	10.5	11.6	12.8
	81–90 km	11	11.2	10.8	8.1	9	14.5	8.1	9.3
	91–100 km	14.5	11.5	10.7	6.8	12	6.1	11.5	8

Figure 9 SDLP values over distance traveled. The left Figure shows SDLP values calculated for 10 km segments of 214 subjects who drove after receiving placebo (Data from references ¹¹, ¹², ¹⁷, ¹⁸, ²², ²³). The right panel shows SDLP values obtained after 1, 4, and 8 hours of continuous driving (Data from reference ²⁷).

Figure 10 The impact of mean lateral position changes on SDLP.

Abbreviations: MLP, mean lateral position; SDLP, standard deviation of lateral position.

Figure 11 Subjective assessments completed after the driving test. Subjects indicate their perceived driving quality (left figure) and perceived effort (right figure) by placing an ‘X’ at the vertical line.

Figure 12 SDLP differences from placebo (cm) after administration of flurazepam (30 mg). When absolute placebo SDLP values increase, the difference from placebo does not (r = 0.16, n.s.).

Data from reference ³, ¹⁵.

Table 2 Summary of generally observed differences and similarities between the on-the-road driving test, driving simulators, and psychometric tests

	On-the-road driving test	Driving simulators	Psychometric tests
Familiarity with test	High	Medium	Low
Learning effect	Low	Medium	High
Simulator sickness	N/A	Yes	N/A
Risk of accidents	Yes	No risk involved	No risk involved
Motivation to perform test	High	Medium	Medium/low
Unexpected events	Yes	Controlled circumstances	Controlled circumstances
Measures overall vehicle control	Yes	Yes	Isolated skills tested
Duration of the test*	Long	Medium/long	Short
Vigilance decrement*	Yes	Yes	No

Notes:

* In general psychometric tests used in driving research are of short duration and not designed to measure vigilance decrement. There are however psychometric tests, such as the Mackworth Clock test, specifically designed for this purpose.

Abbreviation: N/A, not applicable.

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