The influence of the use of mobile phones on driver situation awarenessByAndrew Parkes, Transport Research Laboratory, Crow thorne, England. &Victor Hooijmeijer, Verkeersadviesburo Deepens en Okkema, Eindhoven, The bstractThe driving performance of 15 subjects in a simulated road environment has been studied both with and without a hands-free telephone conversation. The performance indicators used were choice reaction time, braking profile, lateral position, speed, and situation awareness. The driving task was relatively easy, and the young drivers studies were able to have a hands-free telephone conversation and perform well with respect to lateral position, the variation in lateral position of the car, and speed maintenance. However, significant differences were found in choice reaction time, especially in the beginning stages of the telephone conversation, and in situation awareness. The subjects reacted significantly slower to an unexpected event in the first two minutes of the telephone conversation and were, for a large part of the telephone conversation, unaware of traffic movements around them.
Introduction A survey in the United States has revealed that the vast majority (84%) of mobile phone users believe that using a phone is a distraction and increases the likelihood of an accident (IRC, 1999).
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The same respondents report however that 61% of them use their mobile phone while driving and around 30% use their phone frequently or fairly often. Since mobile phone use in cars is a relatively new phenomenon, and since the effects of mobile phone use on traffic safety are still unclear, laws regarding this subject vary between different countries. Some countries use a mixture of legislation and recommendation, but are not consistent about the difference in hands-free and hand-held phone use.
For example, in Italy only hands-free phones are allowed bylaw during driving. At the same time, however, the use of equipment that restricts the hearing senses (which presumably includes all types of mobile phones) is prohibited. The same situation exists in Spain, whereas in Portugal, Denmark, and Hungary only hand-held use of mobile phones is prohibited by law (Oei, 1998; United Nations, 1998).
Outside Europe, a hand-held prohibition exists in Israel, Malaysia and some states of the U. S. A.
Germany, France, and Sweden are examples of countries in which no rules or jurisprudence a reused to limit the usage of mobile phones during driving (Becker et al. , 1995; Oei, 1998; Pet ica, 1993).
Nevertheless, it is recommended in Finland and the UK to use hands-free phones only (Oei, 1998).
The situation is confused and changing continually.
Only recently, The Netherlands (June 2000) ) have jurisprudence on using handheld mobiles during driving. A driver has been found guilty causing an accident because she was having a phone conversation. It is likely that many other countries will develop case law in this way even if legislation does not exist. At one point, it looked as though the problem for legislators would become easier. Research had highlighted the potential safety problems with driving and using handheld devices, and it seemed that the market was leading to the point at which car manufacturers would integrate well-designed hands free telephones into their vehicles. Many interested experts claimed that driving and holding a car phone conversation was no more difficult than talking to passengers, and so, if the handset were removed, the problem would go as well.
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Unfortunately the market has gone in a different direction. Personal mobile phones are ubiquitous due to aggressive and cheap pricing regimes, but hands free adaption kits for use in vehicles, as yet, are not popular. So the use of handheld devices is actually increasing. Added to this is growing concern that the act of holding acar phone conversation is fundamentally different to other in-vehicle conversations with passengers (Parkes 1991 a and 1991 b).
So, we are not reducing the number of handsets, and even if we did, it is possible the problem will remain.
This paper reports experimental work focused on an aspect of driving performance that has not been looked at in-depth in previous studies. In addition to measures of performance such as driver reaction time and steering ability, we consider higher-order functions that identify not just the ability to control the vehicle, but also to maintain a clear picture of the traffic situation around the driver during a. Method In the experiment, 15 volunteer subjects were used. The subjects were all (postgraduate) students at a UK university, aged 22 to 31 (average age = 24. 0 years, SD = 2. 27 years), with more than 3 years of driving experience, and little or no experience with using a mobile phone while driving.
A static driving simulator was used. A medium sized saloon car stood in front of a purpose-built, cylindrical projection screen. Three projectors produced a horizontal forward field of view of 120^0. The vertical field of view is 40^0. An additional projector, aimed towards the rear of the car gave a 50^0 horizontal x 40^0 vertical image, and provided normal view through the vehicle’s interior and driver-side wing mirror. The images were produced with a frame rate of 20 Hz and a screen resolution of 960 x 620 pixels per channel.
The computer monitoring the car outputs also controlled various elements of feedback to the driver, such as the dashboard lights, engine, road and wind noise as well as the sound of other vehicles in the scene. The route used in the simulation was designed to keep the attention of the driver on the road. A single carriageway in a countryside environment was used, with smooth horizontal and vertical curves equally spread along the track length. Other traffic on the simulated road did not disrupt the movement of the subject car. Int his way, the subject could always drive at the desired speed. However, to make the driving environment as natural as possible a fairly high level of oncoming traffic was simulated.
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Cars also appeared in the rear-view mirror and far ahead of the subject car. The route had a total length of 15. 5 miles. Measurement of the performance indicators for each subject took place between the 4 th and the 11 th mile. Subjects were instructed to keep the vehicle in the middle of the lane and to keep closely to the mandatory speed limit, indicated by regular roadside speed limit signs, at all times. The subjects were also told that other normal road environment conditions applied, that other traffic would be present and that some severe weather conditions (like wind gusts) were likely to occur.
Subjects were asked a series of questions via the hands-free car phone, and were required to make a verbal response when they felt able to do so. A hybrid test was developed (Hooijmeijer 1999, based on Fox &Parkes 1991) that incorporated numerical and verbal memory, arithmetic and verbal reasoning. The test was extensively piloted and was aimed to be demanding for the subject group. The subjects were not under time pressure, and they were told that their scores would not be used in any part of the analysis of the trial. Two different kinds of ‘unexpected events’ requiring choice reactions were simulated. The first one was green square (presented on two occasions) that appeared on the road in front of the car for approximately 2 seconds.
Subjects had to flash the lights of the car as quickly as possible in response to the green square. The second event was a red square that represented a danger on the road, and the subjects were expected to make an emergency stop immediately. A further indication of the driver performance was given by the braking distance of the car after the appearance of the red square. This is of course directly related to the reaction time of the driver and the speed of the car, but gives extra information about the performances of the driver. Choice reaction time measurements were taken at 5 miles (1 st green square appearance), 6 miles (red square appearance) and 8 miles (2 nd green square appearance).
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Wind gusts were simulated at 5.
5 miles and at 10 miles, from the left side of the road at an angle of 90^0. Both gusts had a speed that gradually increased from zero to 15 mph and then decreased again gradually to 0 mph. In total, each wind gust lasted over a distance of around 500 m. Lateral position and variability were measured, both on straight sections and when there were simulated wind gusts from the side of the vehicle. Speed maintenance was recorded during sections not involving other measures. Another indicator of performance with respect to speed is the adjustment to a change in the mandatory speed limit.
Along the test track the mandatory speed limit changed once from 80 to 50 km / h (at 4. 5 miles) and once from 50 to 80 km / h (at 7 miles) Situation awareness (SA) has been defined as ‘a person’s perception of the elements of the environment within a volume of time and space, the comprehension of their meaning and the projection of their status in the near future’ (Endsley, 1994).
The relation between poor situation awareness and poor performance has been found in several studies (Endsley, 1990; Venturi no et al. , 1989).
There are three different levels of Situation Awareness (Endsley, 1993): Level 1 SA: Perception of the elements in the environment. Level 2 SA: Comprehension of the current situation.
Level 3 SA: Projection of future status. All three levels of SA were measured in this research by questions directed to the subject at two fixed locations at 6. 5 miles and 9 miles after the start of the test. The screen went blank and the simulation was stopped. The subject was then asked SA probe questions. At the moment the screen went blank, one car was in the rear-view mirror and three or four cars were approaching on the opposite lane.
After asking the questions, the simulation was resumed at the same position as when the simulation was stopped. Results one-sample t-test, was used to determine if there was a difference between the reaction time of the subjects in both situations. The test showed for the first green square a t-value of 2. 576 (the critical t-value is 1. 761, df = 14, = 0. 05).
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The mean reaction time to the various stimuli in the phone and no-phone situation Mean reaction time (sec. ) Stimulus Without phone conversation With phone conversation 1 st green square 1. 008 1. 1312 nd green square 1.
115 1. 187 Red square 1. 370 1. 421 The second green square showed however a non-significant t-value of 1. 169 (df = 14 and = 0.
05 = 1. 761).
The reaction time to the red square gave the same non-significant result. The mean lateral position was calculated for each subject from the lateral position of the car between the 4 th and 5. 5 th mile and the 7 th and 8. 5 th mile of track.
A one-sample t-test showed no significant difference in the mean lateral position between the phone and no-phone situation (df = 14, = 0. 05, t crit = 1. 761, t 1 = -1. 390, t 2 = 0. 879).
A further indication of the performances of the subjects is given by the variability in lateral position, estimated by the standard deviation of the lateral position.
The more the subject varies the lateral position, the more implications this might have on traffic safety. The standard deviation for each subject was also calculated for the same two sections as above. A one-sample t-test showed no significant difference between the phone and no-phone situation in each sections. The variance in lateral position was also used to measure the influences of mobile phone usage on the unexpected event of a wind gust. The standard deviation of the lateral position of each subject was calculated from the lateral position of the car from the triggering of the wind gust until 500 metre’s after. A single-sample t-test gave non-significant values of -0.
48 and 0. for wind gust 1 and 2 respectively (with df = 14, = 0. 05, t crit = 1. 761).
Speed was also used to measure driver performance.
The speed of the car in each trial was measured along part of the track. To avoid influences from the emergency stop (red squares) and the wind gusts, the speed of the car was measured in sections without these features. There was no significant difference between trials. I twas also of interest to see if there was a difference in speed adjustment between the two situations, once the mandatory speed limit changes. During the (possible) phone conversation the mandatory speed limit changed once from 80 mph to 50 km / h and once from 50 to 80 km / h . For each subject the speed was recorded every 100 metre’s from 500 metre’s before the mandatory speed limit sign until 500 metre’s after the speed limit sign.
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Analysis showed no difference in mean speeds around the 50-80 km / h change (df = 14, = 0. 05, t crit = 1. 761, t = 1. 13), but a significant difference was found when the speed changed from 80 to 50 km / h (df = 14, = 0. 05, t crit = 1. 761, t = 3.
However, although the mean speeds of the subjects around the speed limit change differed significantly, this does not say anything about how quickly the subjects reacted to the speed change. Therefore, the mean speeds of the subjects were calculated at 100 metre intervals in both the phone and the no-phone situation. These mean speeds are plotted for the 80-50 km / h and the 50-80 km / h speed changes respectively. This shows that there is no observable difference between the mean reaction to the change in speed limit from 50 to 80 km / h in the phone and no-phone situation: both lines show approximately the same pattern. The change from 80 to 50 km / h however seems to be slower in the phone situation: the mean speed of the subjects in the no-phone situation was below the speed limit after almost 100 metre’s.
Mean change in speed as a result of a mandatory speed limit change from 80-50 km / h 01020304050607080-500 -400 -300 -200 -1000 100 200 300 400 500 Distance from speed limit sign (in n metre’s) no conversation conversation Mean change in speed because of a mandatory speed limit change from 50-80 km / h Situation awareness of the subjects was measured by asking the subjects three questions at two fixed locations during the simulation. The questions asked at each location were: 1. Can you tell me what other traffic was surrounding you just before stopped the simulation? 2. Can you tell me the colour of the car that was in your rear-view mirror? 3.
Was the car in your rear-view mirror driving faster than you or not? Performances on the situation awareness task with and without phone conversation (location 1) No. of correct answers; Location 1 WithoutphoneconversationWith phone conversation 2 Critical value p-value Question 1 14 4 13. 89 12. 12.