España

Various kinds of feedback from ISA equip- ment have been studied. Intervening ISA resulted in speeding virtually disappea- ring unless an override function was im- plemented. Informative ISA, on the other hand, seems to have rather little effect on speeding. The effect was in most cases higher when information was combined

with various kinds of warnings in the case of speed violation. In the PROSPER trial it was found that AAP had a consider- ably higher effect than the combination of visual and auditory feedback regarding mean speed and 85 percentile speeds but not regarding speed distribution. In the

Borlänge and Lund trials it was found that

AAP and the combination of visual and auditory feedback had almost the same effect on driving behaviour, but with a slightly better effect of AAP. However, Vlassenroot (2006) found that, in the case of speed violation, the AAP used did not provide sufficient counter pressure to pre- vent speeding. In the INFATI trial it was found that auditory warnings and a flash- ing diode in combination with informative ISA had a significant effect on driving be- haviour. Much smaller effects were found from warning ISA in the TAC Safecar trial, but it might have been due to the fact that there was major focus on speeding in Vic- toria during the trial, and that the drivers were quite conservative. As a general rule, the higher the speed limit, the higher the effect of ISA. However, on roads with low speed limits (30 km roads/20 mph roads) driving behaviour seems to be affected differently from one ISA trial to another. The same tendency can be seen regarding motorways (110, 120, and 130 km roads). Moreover, in the majority of the trials, it was found that the 85 percentile speed de- creased more than did the mean speed - thus, reduced speed deviation and hence a positive safety effect besides the reduced high speeds, could be expected from ISA. Many ISA trials had shown significant re- sults regarding speeding, but results differ from one trial to another, and one should be careful about benchmarking. Different

types of ISA equipment were used as well as different approaches for measuring the effect, but also different driving cultures and other elements might have affected the results. After long-term use of ISA the effect in general decreases. However, the amount of speeding was in most trials still kept far below the level reached without ISA, as long as ISA was active. Incentive for drivers to avoid speeding seems to in- crease the effect and make it last longer, however, the size of the incentives seems to be less important. In a few trials, the effect of ISA on transportation time was studied. Even though it reduces speeding substantially, ISA has virtually no effect on transportation time.

The safety effects of ISA are considerable. It was estimated that informative ISA can reduce the number of injury accidents by 10%, while the reduction in fatal accidents was estimated at 18%. Most estimation suggested a reduction in the number of in- jury accidents of 18 to 25% when AAP or similar efficient ISA equipment was used. However, lower estimates were found for less busy road types. Regarding interven- ing ISA, the estimated effects are a reduc- tion by between 23 and 42%, and an even bigger reduction can be archived if vari- able or dynamic speed limits are imple- mented. Moreover, when approximately 10% of the cars in Umeå were equipped with warning ISA, an uncertain reduction of 5 to 7% in the number of fatality and injury accidents on roads in built-up areas was reached.

The studies of attitudes towards ISA were carried out in a number of different ways. Therefore, one should be careful when

comparing the drivers’ experiences from different trials. However, where the at- titudes among ISA drivers and non-ISA drivers were compared it was in most cases found that participating drivers were more positive towards ISA than other dri- vers. Also, it was found that the more in- tervening an ISA system was, the lower was the acceptance of it. Furthermore, in studies where the rating of usefulness and satisfaction was the focus of interest, use- fulness was found to be higher than satis- faction. This might mean that the drivers would like ISA to be used by some groups of drivers, but not by themselves. The lat- ter fits well with the results of more gene- ral studies of attitude to driving behaviour and risk, which also show discrepancy be- tween how people assess their own driving compared to other drivers’. E.g. Várhelyi (1996) found that a clear majority (76%) of Swedish road users found that it was less risky if no one violates the speed limit. However, only 36% found that the same problem was associated with their own speed limit violations. Also, in the Euro- pean questionnaire-based study SARTRE

III, on average 63% of the respondents

found that their driving behaviour was less dangerous than the average driver’s (Cau- zard 2004). Furthermore, in the Belonitor trial, 11% of the respondents saw speed- ing as a social problem, but only 2% saw it as a personal problem (Hattem, Mazureck 2005). Obviously, not all these statements can be reliable. Driver attitudes combined with the significantly higher rating of use- fulness than of satisfaction among drivers in some ISA trials are presumably the key reason why ISA has not caught on among the general public so far. In a number of trials, the youngest drivers were underre-

presented for various reasons. Thus, in one trial the drivers had to be at least 25 years old. Also, low interest and high drop out rates have been found regarding young drivers. Furthermore, young drivers own older vehicles in which integration of ISA is difficult, which resulted in a lower pro- portion of young drivers in some of the Swedish ISA trials.

Reliability of the results

Even though most results of ISA were tested regarding statistical significance, there might be an issue regarding reli- ability of the results. In some trials the number of participating drivers was low (15 in the TAC Safecar trial, 20 in each of the PROSPER trials, and 24 in the INFATI trial) (Regan et al. 2006b, Adell, Várhelyi & Hjälmdahl 2008, Lahrmann, Madsen & Boroch 2001). The small groups of drivers might yield less reliable results because a single driver reacting differently could af- fect the results more than if the group of drivers was big. On the other hand regard- ing most trials it was found that the drivers who needed ISA most, e.g. young novice drivers, were underrepresented. Also, it was found in several trials that the partici- pants were more positive towards ISA than was the average driver. Despite this possi- ble bias, it seems reasonable to consider results based on a low number of drivers as reliable. The fact is that, according to studies, most drivers have more or less the same attitude to speeding and speed li- mits. Also the fact that almost all results of ISA are consistent with each other (posi- tive effect of ISA on speeding) indicates that the results are reliable. Another issue is whether a penetration rate of 100% for ISA will result in the same total effect on

driving as it did for the participating dri- vers. On the one hand there might be a bigger effect because the average driver is liable to speed more than the participating drivers. On the other hand there might be a reduced effect because the average driver has a lower acceptance of ISA than have the participating drivers.

2.5 Initiating problem identifi-