Alessandro Calvi

Analysis of driver speeds under night driving conditions using a driving simulator

PROBLEM Accident statistics demonstrate that there should be a greater focus on nighttime driving to improve our knowledge of driver behavior under poor lighting conditions. However, the current geometric design criteria do not take into account driving at night. Moreover, studies that propose predictive models of operating speed only consider daytime driving conditions. METHOD This study compares driver speed behavior during daytime and nighttime driving and models operating speeds and speed differentials, identifying significant factors that influence speed behavior under different lighting conditions. The research was carried out using a driving simulator for a section of an existing two-lane rural road composed of 39 tangent-curve configurations. Speed profiles were recorded for 40 drivers under simulated daytime and nighttime driving conditions. RESULTS New predictive speed models, differentiated for daytime and nighttime driving, are proposed that highlight the effects of different geometric predictors under different visibility conditions. Specifically, predictive models for operating speed on curves identified the inverse of the radius and the deflection angle of the curve as predictors under both driving conditions. For speed differentials based on the 85th percentile for maximum speed reduction (85 MSR), we found that the inverse of the approaching tangent length and of the curve radius significantly explained the dependent variable in both cases, with a higher dependence of nighttime 85 MSR on the curve geometry than on the tangent length. Tangent length had a significant effect on operating speed for independent tangents only for the daytime model, whereas the inverse of the previous radius was confirmed as a predictor for both visibility conditions. PRACTICAL APPLICATIONS This research may influence design considerations for nighttime driving by providing evidence of the effects of nighttime conditions on driver speed choices and road safety.

Effects of simulated day and night driving on the speed differential in tangent-curve transition: a pilot study using driving simulator

Objective: The pilot study described in this article aimed to analyze the driver speed profile for evaluation of road design consistency during simulated day and nighttime driving. The research, carried out using a driving simulator, was developed with the overall objectives of evaluating the speed differential during simulated nighttime driving for the identification of critical road situations not detected by design consistency evaluation during simulated daytime driving. Methods: An existing 2-lane rural road, where high accident rates were recorded during nighttime, was implemented in the driving simulator of the Inter-University Research Centre of Road Safety (CRISS) and the drivers’ speed profiles were recorded in both simulated day and nighttime driving conditions over the 39 tangent–curve configurations that composed the road alignment. Results: The analysis of the speed differential based on the 85MSR (Maximum Speed Reduction) indicator during simulated daytime driving was not able to identify critical road situations that the same analysis revealed during the simulated nighttime driving. Such results occurred for most of the tangent–curve configurations. Conclusions: The study demonstrated that limiting the speed analysis only to daytime driving conditions cannot exclude the possibility that during nighttime driving some road configurations could become unsafe. The findings of the study highlight the need to carry out design consistency evaluations for nighttime driving conditions.

Effects of Mobile Telephone Tasks on Driving Performance: A Driving Simulator Study

Mobile phone use while driving is increasing among road users. Although the most of countries made illegal the cell phone use while driving, the drivers still use it both for calling and texting. Several studies investigated the distraction factors related to the use of mobile while driving and the effects on road safety. The main findings of these studies generally demonstrated an increasing of reaction time and decreasing of driving performance especially during not critical driving conditions, while the evaluation of the effects of mobile use during critical driving conditions is not so much investigates. The overall objective of this work is to contribute to the evaluation of the effects of the mobile phone use on driving safety. Specifically the effects of using cellular phone at the same time the driver is faced with making a critical stopping decision are investigated. The experiments are carried out using an interactive driving simulator. Three different road scenarios (urban road, rural road and motorway) are simulated. Thirty subjects take part to the experiments and drive four times each scenario: one time without calling (control scenario) and the other three times answering the calls by hand-held mobile, hands-free mobile and hands-free voice device. The drivers reaction time, the deceleration rate, the speed and the following distance are evaluated. The main effects of driving and calling are observed in the urban scenario, where the decreasing of driving performance is much more evident than in the rural and motorway scenario. Not significant differences on driving performances are found across the three telephone modes. Keywords - mobile phone, hand-held, hands-free, reaction time, driving simulator, driver distraction Language: en

A Study of the Effects of Road Tunnel on Driver Behavior and Road Safety Using Driving Simulator

The present paper wants to contribute to the knowledge of the tunnel effects on driving performance and safety using the advanced technology of driving simulator. Specifically this study presents the first results of a wider research aimed at establishing how drivers behave inside road tunnel as well as approaching it and exiting from it. Moreover the study verifies a correlation between accident rates and an advanced indicator of simulation computed inside tunnel sections. A highway scenario with eight existing tunnels is reproduced in CRISS driving simulator and several driving parameters are recorded among a sample of twenty-five drivers. Tunnel scenario (TS) data are processed and compared with those of a control scenario (CS), characterized by the same road geometries and alignment of the first one, but without any tunnels. Results confirm previous findings of naturalistic and simulator driving studies about drivers performance inside road tunnels, with significant differences of longitudinal speeds, acceleration and lateral position recorded along the TS and the CS. Moreover the literature safety indicator of driving simulation Pathologic Discomfort (PD) is computed in order to 1) assess the length of approaching and exiting sections of road tunnel and 2) verify PD correlation with the accident rate recorded inside each tunnel. Simulator limitations and future directions of the research are discussed in order to provide guidelines for practical application to road tunnel design and safety measures, taking in account driving performance.

Driver Behavior on Acceleration Lanes: Driving Simulator Study

Acceleration lanes provide access to freeways with the aim of improving traffic flow conditions and safety. Therefore, provision of an appropriate entrance ramp and acceleration lane geometry that allows the entering vehicle to accelerate to a speed closer to the main flow speed is crucial for comfortable and safe merging maneuvers. This paper presents an analysis of driver behavior on different acceleration lanes in various traffic conditions performed on an interactive driving simulator. Three different traffic volumes combined with two lengths of acceleration lane were simulated and their effects on driving performances have been studied. It has been observed that driver behavior during merging maneuvers is significantly influenced by traffic volume on the main lane and that the acceleration lane length does not show any significant effect on drivers’ speed, trajectories, and accelerations. In particular, as the traffic volume increases, so does the merging length of the driver; the acceleration oscillations and the number of gaps rejected also increase. The general results show that the advanced techniques of driving simulation can disclose the relationships between road design parameters and behavioral aspects important to create safer road infrastructure. Further simulation studies are planned to confirm the findings and to strengthen and generalize the results.

A Study on Driving Performance Along Horizontal Curves of Rural Roads

Several studies have indicated that road crashes are more likely to occur on horizontal curves than on straight roadway segments for a good number of reasons, the most important of which is associated with the drivers behavior along the curve depending on his or her perception of the road geometry. However, the evaluation of the effects of curve features on driving performance still remains a critical issue for road safety and design. The main objective of this study is to investigate drivers behavior and his perception of road curves, which is directly related to road safety. Specifically, the effects of some curve features (radius, transition curve, visibility, cross-section) on driving performance are investigated through a multifactorial experiment based on driving simulation. The driving speeds and trajectories of a sample of 34 drivers were statistically processed over 72 different curves distributed along three test scenarios. The main and interaction effects of the independent variables are described and discussed in the Results section providing a significant improvement of the actual knowledge in this field of research. In general, the results confirm that driving simulation can disclose the relationships between road design features and driver behavioral aspects that are crucial issues in creating a safer road infrastructure.

Diverging Driver Performance Along Deceleration Lanes: Driving Simulator Study

Highway diverge areas are often characterized by high crash rates. Worldwide, geometric design guidelines propose deceleration lanes with a parallel or tapered layout to promote a free-vehicle condition, while the guidelines neglect the potential effects of traffic flow and risky driving behaviors that are induced by the wrong perceptions of road geometry and vehicle interference. A driving simulation study was conducted to analyze the effects of traffic flow and deceleration lane geometry on the driving performance of diverging drivers. Two types of deceleration lanes (parallel and tapered) were implemented in a simulator, and two traffic conditions (low and high traffic flows) were simulated for each type of lane. Thirty-one drivers took part in the experiments. The effects of traffic flow on driving performance while drivers approached the diverge area and during their deceleration were investigated. The study found that lane type significantly affected the speeds of diverging drivers, independent of traffic conditions, with greater interference with the through traffic on the tapered lane. Traffic conditions were found to influence the drivers trajectory along the tapered lane, and this trajectory delayed the exiting maneuver under heavy traffic conditions. This effect was not found to have been significant for parallel deceleration lanes on which the deceleration rates were significantly affected by traffic conditions: higher decelerations were recorded under light traffic conditions. No significant traffic effects on deceleration rates were found on the tapered lane.

Laboratory investigations for the electromagnetic characterization of railway ballast through GPR

Ballast material typically employed in rail track bed construction has been herein physically and electromagnetically characterized. Several ground-penetrating radar (GPR) tests have been carried out in a laboratory environment, wherein a proper set-up was realized. Four GPR systems comprising five different central frequencies of investigation have been used for the measurements. The impacts brought to the values of relative dielectric permittivity by the combination of several parameters, namely, i) radar systems, ii) frequencies of investigation, iii) scenarios of ballast stones arrangement, and iv) methods of dielectric permittivity estimate, have been here analyzed. The results have proved the sensitivity of the antenna frequencies and radar systems here employed towards some critical factors.

An empirical study on traffic safety indicators for the analysis of car-following conditions

The likelihood that a car-following driving condition can lead to a rear-end collision is usually assessed through the Time Headway (TH) and Time To Collision (TTC), considered as safety indicators of traffic conditions. The present study computed and compared TH and TTC on the basis of data recorded by means of a traffic control system of an Italian highway. Specifically four measurements sites were investigated for two days and almost 200000 travelling vehicles were collected. About 50% of vehicles were travelling in car-following conditions. The overall objectives of this paper consisted in verifying if, on highways, TH and TTC are independent of each other and, therefore, do not provide the same information on the driver behaviour in car-following situation but could be used for evaluating different conditions. Moreover the effects of different visibility conditions (day or night driving), the type of lead vehicle (passenger car or heavy vehicle) and the type of travelling lane (left or right) on TH and TTC were evaluated in order to increase the knowledge of drivers behavior in car-following conditions. The results demonstrated that TH and TTC provide different information on driver behaviour in carfollowing conditions as they can be considered practically independent of each other. Moreover it was found that shorter THs are used by the following driver during daytime, behind passenger vehicle and driving on the passing lane. On the contrary only few cases with critical TTC values were recorded, demonstrating that TTC is more effective for detecting impending dangerous situations. Language: en

Evaluating the effects of the number of exit lanes on the diverging driver performance

ABSTRACT This study investigated the driving performance of drivers exiting from the highway under various geometric deceleration lane conditions. Specifically, the effects of different deceleration lanes on the speeds, trajectories, and decelerations of diverging drivers were investigated to increase the knowledge of driver behavior while approaching a highway exit, during the lane-change maneuver, and along the deceleration lane. Thirty-one drivers took part in the experiments. Two different tapered deceleration lanes (with a single-lane exit ramp and with a two-lane exit ramp, respectively) were implemented using a driving simulator to observe how exiting drivers performed, by analyzing their speeds, decelerations, and trajectories. The main results demonstrated that, for the geometric and operating conditions investigated in this study, a single-lane exit ramp resulted in a poorer performance from the exiting drivers with regard to the operating and safe driving conditions. In fact, it was found that, when a single-lane exit ramp was available, drivers adopted lower exiting speeds and higher decelerations than those using a two-lane exit ramp. Therefore, the latter seemed to provide improved performance, by limiting the interferences of the diverging drivers with through traffic.