FINNCONTACT 3/95

Quarterly Newsletter of the Finnish Highway Transportation Technology Transfer Center, FinnT2
Address: Finnish National Road Administration, FinnT2, P.O. Box 33, 00521 Helsinki, FINLAND
Fax Int. 358 204 44 2675. E-mail: [email protected] Editor: Arto Tevajarvi, Tel. Int 358 204 44 2032
Editor-in-Chief: Jarmo Ikonen, Tel. Int. 358 204 44 2118

EFFECTS OF STUDDED AND UNSTUDDED WINTER TYRE ON DRIVER BEHAVIOUR

The Road Traffic in Winter Research Project also included some interesting behavioural studies. The effects of studded and unstudded tyres on drivers general and operational behaviour patterns under different winter road conditions proved to be a beneficial source of information.

DATA ON THREE DIFFERENT LEVELS

The study dealt with comparing driving behaviour with studded and and unstudded winter tyres. The duration of the study was a two winter period. In the course of this time driving behaviour on three levels was monitored: 1) Effects on strategical behaviour, such as exposure and use of other transportation modes 2) Effects on tactical behaviour, such as timing of the trips and type ot route selected 3) Effects on operational behaviour, such as speed, braking and headway.

SELF-MONITORING AND UNOBTRUSIVE MONITORING

The subjects (drivers), 120 ill all were selected out of about 2 000 volunteers l)icked up from the vehicle register. The sub jects were divided into two groups by tyre types used. Each subject was given a set of winter tyres tor his/her own car. Then, the drivers were issued a log for recording all their daily trips during the period of a combined eight weeks in two winters. The actual driving tests were carried out with two instrumented cars, and 68 subjects participated in this part of the experiment. The instrumented cars were used in an unobtrusive way. So, all the measuring instruments were hidden in the cars and drivers were given a cover task. The drivers were not informed of the true meaning of the tests until the end of the last driving task.

The purpose of this arrangement was to improve the validity of results. One of the problems in driver behaviour monitoring is that the awareness of being the object of monitoring changes behaviour, and consequently produces biased results. An experimental design was used so that the baseline measurements comprised all drivers driving with studded tyres. During the first and the second winter, studless drivers were using the test car with studless tyres and those having studded tyres on their own cars were driving the test car equipped with studded tyres respectively. Totally, some 16 OOO kms of driving with instrumented cars on the fixed, preselected routes in variable winter conditions were recorded. Moreover, the studless and studded drivers were driving pairwise the same route in 10 minutes intervals without being aware of each other.

NO EFFECTS ON TRAVEL HABITS THOUGH CHANGES IN DRIVING BEHAVIOUR

It turned out that when drivers started to use unstudded winter tyres, it had no effects on travel decisions. The number of trips, the length of trips, the timing of trips and the routes selected were totally unaffected by the change in the tyre type. These results were corroborated during the second test winter.

On the other hand, there were clear behavioural changes recorded by the instrumented cars.

In general, unstudded tyre drivers were driving somewhat more carefully on slippery road surfaces and less carefully on bare road surfaces than the control drivers with studded tyres.

On motorways under good driving conditions, speed levels clearly increased during the first winter. Unstudded tyre drivers were driving 5-6 km/h faster than the control drivers using studded winter tyres. On slippery road surfaces, when negotiating steep curves and on approaches to splippery intersections, drivers using unstudded winter tyres were driving 2-4 km/h slower than the control drivers. Those using unstudded tyres were also keeping longer headways with vehicles in tront. While the mean headway for the unstudded drivers was 45 meters, the respective figure for the studded drivers was 34 meters in the platoon travelling at the speed of about 70 km/h. Moreover, unstudded drivers were braking more gently than the control drivers under very slippery conditions, but the difterence in the frequency of using the brakes was marginal between the two groups.

Drivers in both groups also recorded incidents they classified as problematic or risky when driving their own cars. There was not a statistically significant difference between the groups.

It seems, to some extent, that drivers take into account the type of tyres they are using. Also the compensation is not sufficient under all conditions, especially at intersections. Moreover, the increased speed levels of unstudded drivers under good driving conditions may potentially create more accidents when the results are projected to the whole driver population.

TAPANI M�KINEN
Technical Research Centre of Finland

Contents of FinnContact 3/1995:

Top
[Paluu etusivulle]
[Back to main page]