The use of navigation systems in naturalistic driving

Figures & data

Table 1 Characteristics of trips for which participants did or did not use the navigation system

	Without navigation system		With navigation system		T-test (df = 20)
Trip characteristic	Mean	SD	Mean	SD	t	P
Number per participant	47.9	20.3	14.3	9.5	−6.32	.00
Distance driven (km)	13.8	8.8	40.7	21.3	−5.79	.00
Duration (s)	1,249.0	487.8	2,661.4	938.2	−6.48	.00
Mean speed (km/h)	31.7	7.8	52.4	11.2	−7.00	.00
% of time on urban road	64.7	12.8	48.2	15.5	3.93	.00
% of time on rural road	13.0	10.8	16.7	7.6	2.16	.04
% of time on motorway	12.6	9.6	34.4	15.6	−6.34	.00
% of time road type unknown due to incomplete map	9.7	7.3	0.7	1.8	5.46	.00

Table 2 Mean speed for several speed limits, with and without use of the navigation system

	Trips with the navigation system		Trips without the navigation system
Speed limit (km/h)	Mean speed (km/h)	SD	Mean speed (km/h)	SD
50	23.4	4.9	20.1	4.3
70	59.3	13.2	62.6	16.4
80	61.9	10.4	58.3	13.1
100	87.3	11.6	85.7	9.6
120	86.3	17.3	78.2	18.8

Table 3 Mean percentage of trips for which the navigation system was used in several time-related units

	Proportion of trips for which navigation system was used
Temporal unit	Mean (%)	SD (%)
Weekday (Monday–Friday)	24.0	17.2
Weekend day (Saturday, Sunday)	25.6	19.3
Monday	23.0	22.7
Tuesday	25.0	19.7
Wednesday	28.9	23.9
Thursday	21.4	25.9
Friday	19.3	22.2
Saturday	24.6	25.4
Sunday	34.6	33.7
First trip of the day	26.9	17.6
Last trip of the day	19.0	18.1
Other trips	27.0	20.8
Morning peak (7:00 a.m.–10:00 a.m.)^a	34.1	29.4
Afternoon peak (4:00 p.m.–7:00 p.m.)^a	21.2	20.4
Off-peak/other hours^a	25.4	19.6
Night (12:00 a.m.–6:00 a.m.)	n/a^b
Morning (6:00 a.m.–12:00 p.m.)	29.3	20.9
Afternoon (12:00 p.m.–6:00 p.m.)	25.3	18.9
Evening (6:00 p.m.–12:00 a.m.)	17.3	17.4

^aExcludes weekends.

^bOnly 9 trips fit this criterion.

Table 4 Percentage of time that drivers exceeded the speed limit, driving with or without a navigation system

		Trips with the navigation system		Trips without the navigation system
		Mean percentage	SD	Mean percentage	SD	T-test (df = 20)	Effect size (r)^a
>50% over speed limit	Overall	0.6	0.5	0.5	0.4	NS	0.13
>20% over speed limit	50	4.6	2.7	3.2	2.4	NS	0.41
	70	10.9	11.9	14.7	20.3	NS	0.17
	80	3.9	4.1	3.3	4.9	NS	0.22
	100	5.9	8.0	5.0	7.2	NS	0.17
	120	0.2	0.4	0.1	0.2	NS	0.28
	Overall	4.1	2.8	3.2	2.6	NS	0.40
All speeding (any speed above the speed limit)	50	12.2	5.4	9.7	4.1	NS	0.40
	70	29.2	17.9	31.6	21.0	NS	0.10
	80	22.2	13.4	19.2	14.0	NS	0.21
	100	34.6	20.3	37.0	22.9	NS	0.14
	120	15.2	18.4	15.5	19.7	NS	0.03
	Overall	20.4	11.7	14.8	7.8	2.61, P = .017	0.50

^aEffect size r is calculated using r

Table 5 Visual–manual task characteristics, as coded from the video data (see Methods/Data Analysis sections for definitions)

	Reach, grab, mount		Destination entry		Other operation
	Mean	SD	Mean	SD	Mean	SD
Total number of times the task was performed	11.5	10.3	18.1	14.3	31.9	28.0
Repetitive trips	2.6	3.6	5.9	8.0	7.1	10.7
Unique trips	8.9	8.2	12.2	9.2	24.8	22.8
Task completion time (s)	12.0	4.7	26.6	12.9	15.3	9.7
Number of actions performed during trips for which system was used	0.7	0.4	1.3	0.4	2.2	1.2
% of driving time engaged in task (during trips for which system used)	0.8	0.4	2.4	1.1	2.0	1.2
% of driving time engaged in task (for all trips)	0.1	0.1	0.5	0.5	0.5	0.5

Figure 1. On which part of the trip did visual–manual tasks start? (See the Data Analyses section for a detailed description of these tasks.) To determine the trip time segment to which each operating event belonged, the following formula was used: