Francesco Bella

Driving simulator for speed research on two-lane rural roads

The paper reports on a validation study of the interactive fixed-base driving simulator of Inter-University Research Center for Road Safety (CRISS) that was effectuated in order to verify the CRISS driving simulators usefulness at a tool for speed research on two-lane rural roads. Speeds were recorded at eleven measurement sites with different alignment configurations on a two-lane rural road near Rome. The real world was reproduced in the CRISS driving simulator. Forty drivers drove the simulator. The results of the comparative and statistical analysis established the relative validity and also revealed that absolute validity was obtained in nine measurements sites. Only in two non-demanding configurations, were the speeds in simulator significantly higher than those recorded in the field. In these sites the mean speed in simulator was equal to or greater than 94 km/h. For these configurations, the higher speeds recorded in simulator appeared to stem from the different risk perception on the simulated road as opposed to that on the real road. The studys results should be considered for driving speed behavior research, in which simulator equipment with similar features of the CRISS driving simulator is used.

Validation of a driving simulator for work zone design

The research project aimed at calibrating and validating the driving simulator of the European Interuniversity Research Center for Road Safety to enable its use for design and verification of the effectiveness of temporary traffic signs on highways. The research was developed through the following steps: (a) a survey of speed measurements on highways next to a work zone of medium duration, (b) reconstruction in virtual reality of the real situation by using the driving simulator and subsequent running of a series of driving tests, and (c) statistical analysis of the field speeds and of the speeds from driving simulations for validation of the simulator. The surveyed work zone was located on Highway A1 from Milan to Naples, Italy. Speed measurements were conducted with a laser speed meter in the transition area, the activity area, and the termination area, and in the advance warning area speeds were shot with a camera from an overpass. Speed data from the field and the simulator were analyzed by using the bilateral Z-test for nonmatched samples to determine whether drivers responded differently in the simulator compared with their response during the real driving experience. The activity carried out revealed that differences between the speeds observed in the real situation and those measured with the simulator were not statistically significant.

Can Driving Simulators Contribute to Solving Critical Issues in Geometric Design

Research on driving simulation in virtual reality has not been recommended by strategic documents for solving critical issues in geometric design. However, several research efforts have demonstrated the usefulness of driving simulators in road design. The objective of this paper is to initiate a discussion on the effective contribution of driving simulators to issues of geometric design. The paper gives an overview of the main experiences acquired in geometric design using advanced driving simulators and points out their potential as well as their limits. It then outlines the critical issues in promoting their use in geometric design and provides recommendations for overcoming these issues.

Time domain reflectrometry: Calibration techniques for accurate measurement of the dielectric properties of various materials

In this work, an extensive theoretical and experimental analysis has been carried out on the main factors that affect the accurate evaluation of dielectric properties using time domain reflectometry (TDR). Dielectric constant measurements have been performed under different experimental conditions for various types of materials having a wide range of permittivity values. Interpretation of the results on the basis of the transmission-line theory emphasizes the importance of a suitable calibration procedure that takes into account several critical aspects, some of which seem to have been disregarded or underestimated in the literature. Qualitative and quantitative information is given on the kind of corrections needed in order to significantly improve the reliability of the TDR technique for permittivity measurements.

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.

Parameters for Evaluation of Speed Differential: Contribution Using Driving Simulator

This paper describes the results of a study performed with the interactive fixed-base driving simulator of the Inter-University Research Center for Road Safety and seeks (a) to select, from the parameters proposed in the literature for the evaluation of the speed differentials between tangents and curves, those that best reflect the real speed reductions experienced by drivers and (b) to develop new models for estimating speed differential values. Thirty people drove the driving simulator on a two-lane rural road with 16 different tangent-curve configurations. On the basis of measured speeds, the parameters were calculated for the 85th-percentile of the distribution of maximum speed reduction experienced by each driver (85MSR) as well as the differential speed not exceeded by 85% of the drivers traveling under free-flow conditions (Δ85V). The statistical analysis performed reveals that the differences between the two parameters were statistically significant and, in so doing, indicates that using Δ85V to measure speed differentials leads to an underestimation of the speed differences adopted by drivers. Three speed differential predicting models were also developed. The models being proposed are similar to those in the literature. These models show that speed differentials are influenced by the same variables that were uncovered in previous field research. The results of the present study corroborate the outstanding potential of the driving simulator as a useful instrument for the analysis of speeds on two-lane rural roads as well as for the effects of road alignment configurations on drivers.

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 safety measures on driver's speed behavior at pedestrian crossings

This paper reports the results of a multi-factorial experiment that was aimed at the following: (a) analyzing drivers speed behavior while approaching zebra crossings under different conditions of vehicle-pedestrian interaction and with respect to several safety measures and (b) comparing safety measures and identifying the most effective treatment for zebra crossings. Three safety countermeasures at pedestrian crossings (curb extensions, parking restrictions and advanced yield markings) and the condition of no treatment (baseline condition) were designed on a two-lane urban road and implemented in an advanced driving simulator. Several conditions of vehicle-pedestrian interaction (in terms of the time left for the vehicle to get to the zebra crossing at the moment the pedestrian starts the crossing) were also simulated. Forty-two drivers completed the driving in the simulator. Based on the recorded speed data, two analyses were performed. The first analysis, which focused on the mean speed profiles, revealed that the drivers speed behavior was affected by conditions of vehicle-pedestrian interaction and was fully consistent with previous findings in the literature and with the Threat Avoidance Model developed by Fuller. Further analysis was based on variables that were obtained from the speed profiles of drivers (the speed at the beginning of the deceleration phase, the distance from the zebra crossing where the deceleration began, the minimum speed value reached during the deceleration, the distance from the pedestrian crossing where the braking phase ended and the average deceleration rate). Multivariate variance analysis (MANOVA) revealed that there was a significant main effect for safety measures and for pedestrian conditions (the presence and absence of a pedestrian). The results identified that the curb extension was the countermeasure that induces the most appropriate drivers speed behavior while approaching the zebra crossing. This conclusion was also confirmed by outcomes of the questionnaire on the countermeasures effectiveness. More than 80% of the drivers perceived that the curb extensions were effective, which indicates that when this countermeasure was present, the drivers were more willing to yield and that the visibility of the pedestrian crossing was better. For this countermeasure, the lowest number of interactions in which the drivers did not yield to a pedestrian was also recorded.

Driver Performance Approaching and Departing Curves: Driving Simulator Study

Objective: This article reports the outcomes of a driving simulator study on the driver performance approaching and departing curves. The study aimed to analyze driver performance in the tangent–curve–tangent transition and verify the assumption of constant speed in a curve that is commonly used in the operating speed profiles; test whether the 85th percentile of acceleration and deceleration rates experienced by drivers and the acceleration and acceleration rates obtained from the operating speeds are equivalent; find the explanatory variables associated with the 85th percentile of deceleration and acceleration rates experienced by drivers when approaching and departing horizontal curves and provide predicting models of these rates. Methods: A driving simulator study was carried out. Drivers’ speeds were recorded on 26 configurations of the tangent–curve–tangent transition of 3 2-lane rural roads implemented in the CRISS (Inter-University Research Center for Road Safety) driving simulator; 856 speed profiles were analyzed. Results: The main results were the following: The simplified assumption of the current operating speed profiles that the speed on the circular curve is constant and equal to that at midpoint can be considered admissible; The 85th percentile of deceleration and acceleration rates exhibited by each driver best reflect the actual driving performance in the tangent–curve–tangent transition; Two models that predict the expected 85th percentile of the deceleration and acceleration rates experienced by drivers were developed. Conclusions: The findings of the study can be used in drawing operating speed profiles that best reflect the actual driving performance and allow a more effective safety evaluation of 2-lane rural roads.

Operating speeds from driving simulator tests for road safety evaluation

Two-lane rural roads with features consistent with those required by Italian guidelines for major two-lane rural roads were implemented in a driving simulator. Twenty-nine tangent-curve-tangent configurations similar to those where a previous validation study ascertained the validity of the driving simulator for driving speed behavior research were selected. The drivers’ speeds on these configurations were processed to obtain the operating speeds. The main findings were the following. The maximum operating speed on the last 200 m of the approach tangent (V85max_200) is higher than the operating speed at the midpoint of the tangent (V85mid,t). The operating speed at the midpoint of the curve (V85mid,c) overestimates the minimum operating speed of the drivers on the curved section (V85min,c). Therefore, V85max_200 and V85min,c are the most appropriate parameters for the quantification of the speed differential as difference between the operating speeds on the approach tangent and on the successive curve. A positive correlation was found between V85max_200 and the length of the tangent whereas a negative correlation was found for the longitudinal grade. Two operating speed models for curves were obtained. Such models were validated using the speeds that were recorded by means of a Global Positioning System device on six configurations of a real two-lane rural road.