Application of driving simulators
By means of its simulators the institute has investigated for example how new technology, sound and vibrations affect driving. The driving simulators have also been used in the planning of Stockholm's traffic system, among other things to determine where signs should be located and how the surroundings should be designed.
Areas of application
The transport sector is facing great challenges and VTI's driving simulators are an important resource in the work of improving infrastructure, traffic and transportation. They can for example be used for:
- product and system development
- road design
- developing new car concepts, e.g. electric cars
- research on behaviour and evaluating safety functions for collision situations.
Below a selection of simulator studies carried out in VTI's simulators is presented. Some of these studies are subparts of a larger project while others are the main activity of the funding project.
Accident statistics assembled by VTI have shown that buses are overrepresented when it comes to accidents on icy and snowy roads. For a better understanding of the problem, the performance of modern summer and winter tyres on winter road conditions had to be assessed.
The objective of this work has been to go beyond standard road grip studies, and instead investigate how the driver's possibility to deal with one challenging situation depends on the tyres and tyre configuration. This study utilised a novel methodology where measurements of different tyres on ice in VTI´s tyre test facility enabled a simulator study for evaluating the impact of different tyre characteristics when driving in conditions with strong side wind on a slippery road.
A driving simulator scenario was chosen where the driver is exposed to strong side wind gusts, when driving at high speed on an ice covered road. To collect data from different tyres VTI's tyre test facility was used. The measurements were used to create a model that characterises the wheel, and which could be used for a real time simulation. For this Pacejka's magic formula in combination with a model to account for the tyre relaxation length was used. A bus vehicle model was implemented in Sim II, and the experiment was conducted with five test persons. Each person had to drive on a straight ice covered road, experiencing sudden wind gusts of different strength, while using different tyre combinations.
To deal with strong side wind, good front wheel grip is most important, and while non studded winter tyres provided little or no improvement over summer tyres, studded winter tyres significantly reduced the risk to run off the road. Furthermore, it is very difficult for the drivers to judge, beforehand, whether a vehicle with a particular tyre configuration will perform good or bad.
Hjort, M. & Jansson, J. (2008). Handling of buses on slippery roads during the influence of side wind – a study of the effects of different tyres. AAP – in press
Hjort, M., Thorslund, B., Sundström, J., Wiklund, M. & Öberg, G. (2008) Traffic safety of buses wintertime. VTI rapport 618, Linköping, Sweden, VTI. (In Swedish)
Within the European project COOPERS (Co-operative Systems for Intelligent Road Safety), new safety related services have been developed. These services utilize primarily infrastructure to vehicle communication as well as an onboard unit presenting the services to the driver.
The purpose of this driving simulator study was to assess the influence of this onboard unit with some of the services on driver behaviour and user acceptance, by comparing driving with versus driving without the services activated.
The drive took place on a simulated typical Swedish motorway during normal traffic conditions and the stretch was about 40 km long, which resulted in a total driving time of 45-50 minutes for each driver. Each driver had to drive the same stretch twice, one time with the COOPERS information system activated and a second time with an inactive system. During each stretch, the driver was exposed to three different scenarios where the information system would warn the driver: congestion scenario, heavy fog scenario and rapid ambulance transport approaching from behind. At the end of the second drive a fourth scenario was also used, a so called ghost driver situation, where the driver meets a vehicle driving in the opposite direction in his lane on the motorway.
The simulator study, using 48 drivers, showed that the tested system had an effect of reducing the driving speed for all tested scenarios and thus a positive effect on traffic safety. Other changes in driver behaviour that can be considered beneficiary from a traffic safety perspective, like reduced longitudinal and lateral acceleration, were also observed. Overall, the mere presence of the system did not create any changes in observable driver behaviour. The presence of the system seems to have an effect when it is active in the warning phase. The study shows that when the system is active, the drivers adapt to the scenarios according to the information given through the system. The results also indicate that it would be possible to reduce driver stress in traffic by providing the driver with up-to-date information about upcoming traffic events.
M. Hjort, R. Kölbl, and S. Fuchs. Results of the coopers simulator study: A comparison of driver behaviour in different usage groups /simulation results. ITS World 2009 Stockholm.
COOPERS Joint deliverable SWP 4100 and 6500. In preparation.
The project's objective was to develop and test rules and concepts of HMI for multiple active safety systems where the driver will react and respond in an appropriate way to avoid the threat or threats in the specific situation. Three different safety systems were used in the project: a forward collision warning system, a lane departure warning system and a distraction warning system.
Tests with 74 drivers were done in a driving simulator (VTI's Sim III) on a double-lane motorway with a speed limit of 110 km/h. The drivers were informed that the vehicle they drove was equipped with the three active safety systems. A secondary task (Surrogate In Vehicle Information System, S-IVIS) was used to visually distract the driver from looking at the road.
In the scenarios and for the systems tested in this study, warnings did produce appropriate driver responses. This means braking for collision warning, steering for lane departure warning and looking back to the road for distraction warning, also when the warnings occurred simultaneously. There was no evidence found that "Warning Management" influences the drivers‟ reaction and response compared to "No Management" in this setup (no effect by issuing higher priority warnings earlier instead of a lower priority warning and no effect by issuing one warning instead of several). A possible explanation of the driver behaviour could be that drivers react on the warning by looking back to the road, but respond based on their own assessment of the scenario (and not on the interpretation of the warning).
Dukic, T. (2009). Driver Warnings In Time and Safety critical situations. DiWiTSAState of Art. Issue 1. Restricted report. Linköping, Sweden: VTI.
Dukic, T. (2009). Warning management for active safety systems. Restricted report. Linköping, Sweden: VTI.
Dukic, T. & Nilsson, L. (under writing). Warning management for active safety systems. To be submitted to an international journal. Linköping, Sweden: VTI.
This experiment attempts to explore the possibility of using large scale moving based driving simulators to evaluate functions like ESC. This is conducted through a simulator experiment where the subject drivers have been provoked in driving scenarios to ESC interventions.
The experiment indicates the possibility of using driving simulators for evaluation purposes. This implies that studies of the benefits can be performed with higher accuracy regarding repeatability and evaluation testing of active safety functions can be made more cost efficient and without jeopardizing safety of involved driver and other road-users.
The experiment was designed for studying the effects of ESC presence in critical situations. To cover both roll and yaw instability, a closing curve and moose scenarios, were included in the experiment. Due to the limitation to 16 test subjects, a within group design was preferred, i.e. an experimental design where all test subjects would drive both with and without ESC activated, experiencing both driving scenarios with both conditions.
This study was conducted with professional truck drivers that must be taken for highly skilled drivers which most likely makes it harder to design realistic driving scenarios where the driver has a 'loss of control' situation compared to passenger car drivers used in similar ESC simulator experiments. Overall, the subjective criticality estimates are rather low, and 'potential loss of control' was reached only in 28 per cent of curve situations and 22 per cent of moose situations. In future experiments, the scenarios should be tuned more aggressively.
N. Dela, L. Laine, F. Bruzelius, H. Sehammar, L. Renner, G. Markkula and A. Karlsson. A pilot evaluation of using large movement driving simulator experiments to study driver behaviour influence on active safety systems for commercial heavy vehicles. Proccedings of 21st International Symposium on Dynamics of Vehicles on Roads and Tracks (IAVSD'09). Stockholm, Sweden, 2009.
The objective of this study was to implement and validate a basic, yet realistic, ESC system into the VTI simulator environment. The implemented ESC system is used in a study, where the ESC system could be turned on and off, to evaluate the benefits of an ESC system after a side impact.
The experiments consist of two parts. In part 1 the test subjects are faced with a unexpected side-swipe collision. In part two the test subject, now prepared, repeatedly experience the same forces acting on the vehicle while trying to maintain control.
This study shows that an ESC system may aid the driver in such a critical situation when the driver is unaware that a side impact will occur. With the ESC system active no driver lost control while with the system inactive there were five drivers that lost control, but deviations in initial speed give statistical difficulties, thus more tests are needed. In the case where the driver knows that an impact will occur the ESC system showed to stabilize the automobile faster and it is shown that an expected improvement in stabilization time is between 40 to 62 percent. It was also seen during this part of the scenario that 2 percent loss of control occurred with an active ESC system and 45 percent without.
Andersson, A. (2009). Implementation, validation and evaluation of an ESC system during a side impact using an advanced driving simulator. Examensarbete vid Linköpings universitet, LITH-ISY-EX--09/4234--SE.
Many experimental studies use repeated lead vehicle braking events to study the effects of Forward collision warning, FCW, systems. It can however be argued that this experimental design may undermines result validity, at least in terms of generalisability to real-world emergency braking scenarios.
This study's main objective was therefore to examine whether the presence of a FCW system affects driver response times in emergency braking scenarios, and if there is an effect, whether it is moderated by repeated scenario exposure.
A critical lead vehicle braking scenario was implemented in a moving-base simulator, and the effects on driver response times of FCWpresence, two different initial time headways at visual distraction task onset and repeated scenario exposure were examined.
Overall, the study shows that when measuring the effects of a FCW in an emergency lead vehicle braking scenario, the effect size is governed by on one hand the saliency and timing of the warning, and on the other hand by the transparancy of the scenario for drivers who do not receive a warning. Also, the study shows that previous experience of the FCW system has a huge influence on driver behaviour; the unknowing driver responds only to the scenario and not at all to the FCW, while the trained and trusting driver responds primarily to the FCW and to a lesser extent to the scenario.
Ljung M., Engström J., Viström M., Andersson A., Bolling A., Hjort M., Jansson J., Källgren, L. (2009). Effects of forward collision warning, initial time headway and repeated scenario exposure on driver response in emergency lead vehicle braking scenarios. VIP Rapport (in-print), Linköping, Sweden.
One traffic safety problem that has been observed in several studies is the wear of the windscreens. The risk of dazzling increases when driving with a worn windscreen, which may have the consequence that the driver does not discover objects or people on the road in front of the vehicle.
In this simulator study driver behaviour has been studied using three windscreens, one driven 150 000 kilometres, another driven 350 000 kilometresand one unused. The experiment has a within groups design. In this case this means that all 24 test persons drive under each experimental condition, i.e. everyone with each of the three windscreens. The driver passes two obstacles during each drive. To achieve dazzling in the driving simulator a lamp was mounted in front of the windscreen in the simulator. The lamp simulated a setting sun
Already with a windscreen used during 150 000 kilometres the driver behaviour is negatively effected. When the drivers were asked to express their opinion about the experiment, they assessed both the simulated environment and the driving task as relatively realistic.
This project carried out the design and the implementation of a roll stability system for a simulated heavy vehicle. The purpose of the system is to prevent rollover. The making of the system consists of three parts; calculating the roll angle, calculating a rollover index and constructing the control system.
The benefits of the system were measured by conducting a study in which test persons drove the simulator truck both with the stability system switched on and switched off. The scenario in the study was carefully constructed so that it would test the system thoroughly.
The results were not unambiguous, in some situations the roll stability system prevented roll over, but in others it had the opposite effect.
Pettersson, U. (2010). Implementing and studying the effects of a roll stability system in heavy vehicles using a moving simulator. Examensarbete vid Linköpings universitet, LITH-ISY-EX--10/4337--SE.
By means of a driving simulator study in 2004, VTI was able to show that mobile phone calls with a hands-free kit are no safer than calls with a hand-held phone.
The simulator study primarily investigated calls while driving. The results of the study show that drivers' awareness is impacted negatively by phone calls regardless of whether they use a hands-free kit or hold the phone. The participants in the study were themselves considerably more positive to using a hands-free kit than holding the phone while driving. The test subjects perceived their own driving performance as being better when using a hands-free kit than when holding the phone. Despite this, the study showed no differences in driving performance between using a hands-free kit and holding the phone.
Surprised drivers can explain most reported traffic accidents. A simulator study was made to investigate truck drivers' behaviour in critical situations and how they are affected by surprises while driving.
In the study the test subjects drove the simulator for about 30 minutes and then experienced a sudden blow-out on the left front wheel. When the first blow-out occurred the driver was surprised. Another four blow-outs were simulated as the driver continued but on these occasions the driver was prepared.
Both field and simulator studies indicate that it is possible to brake after a blow-out on one of the front wheels. The investigation of how the element of surprise affects driver behaviour would not have been able to be conducted without risk without the driving simulators.
Pettersson H-E. , Aurell J. & Nordmark S. (2006) Truck driver behaviour in critical situations and the impact of surprise – a pilot study of a sudden blow-out on the front axle of a heavy truck. Paris.
The Swedish Transport Administration follows up the condition of state-administered roads regularly by means of road surface measurements. At the same time, questionnaire surveys are conducted among motorists and professional drivers to ascertain how satisfied or dissatisfied road-users are with the operation and maintenance of the state-administered roads. Agreement between the objective measurements that are taken and the road-users' rankings is in general not particularly good.
In order to investigate the importance of the visual, auditive and tactile impression of a rutted road and a patched road, VTI conducted a simulator study. In the study, the test subjects drove a scenario where the condition of the road surface was varied and subjectively estimated how comfortable and safe the road surface was.
The results of the study showed that there is a clear correlation between how drivers perceive a road's comfort and safety. The simulator study demonstrates unambiguously how impressions of visual, auditive and tactile information contribute to a degraded perception of comfort and safety. The results of the study also show great differences between different types of road surface.