George Yannis | National Technical University of Athens (original) (raw)

Papers by George Yannis

ABSTRACT Stopping Sight Distance (SSD) is a key control element which directly affects the sugges... more ABSTRACT Stopping Sight Distance (SSD) is a key control element which directly affects the suggested values of crucial road design parameters. Although there is a significant difference in SSD values between upgrades and downgrades, many Design Policies ignore the grade effect during vehicle braking on variable grades. Such a case is experienced during the determination of crest vertical curvature rates where the relevant SSD values are extracted assuming leveled road geometry. The paper investigates possible deficiency of this approach, regarding cases where the length of the vertical curve exceeds the control SSD values. The authors addressed the SSD calculation on variable grades during the braking process through a recently developed process that relates the point mass model and the laws of mechanics. For a wide range of design speed values, charts illustrating the required SSDs were drawn as a function of negative ending grade values related to control crest vertical curve rates, as adopted by AASHTO. The process revealed numerous SSD shortage areas, where the authors provided revised crest vertical curvature rates, in order to grant SSD adequacy throughout the vehicles’ breaking process. Furthermore, the authors aiming to provide the designers with ready-to-use vertical design tool associated the amended vertical curvature rates to AASHTO’s road functional classification, as a function of the crest vertical curve’s exit grade value.

This paper investigates potential Stopping Sight Distance (SSD) violation for 130km/h vehicle spe... more This paper investigates potential Stopping Sight Distance (SSD) violation for 130km/h
vehicle speed, on the passing lane of divided highways at left horizontal curves
overlapped with crest vertical curves. The authors previously developed a SSD control
methodology that relates concurrently the 3D configuration of a roadway to the
dynamics of a vehicle moving along the actual roadway path. This methodology is
applied for the assessment of critical design parameters directly related to both
demanded and available SSD values. Initially, by utilizing control geometric and driver -
obstacle values adopted by AASHTO 2011 design policy, excessive SSD inadequacy
areas were revealed. Subsequently, on the basis of a classic statistical and
explanatory modeling approach for a number of geometry parameters, an evaluation of
SSD sufficiency was carried out in terms of both the probability of SSD inadequacy and
the prediction of the object height in order to grant SSD adequacy (amended object
height). These models may be useful to researchers and practitioners aiming to
evaluate the interaction of the utilized design parameters in terms of the presence and
the extent of SSD inadequacy. The results suggested that the probability modelling
approach was efficient, yielding a model which enables to correctly assess SSD
adequacy (by more than 94%) in such 3D road alignments. The lognormal modelling
approach for the prediction of the amended object height (AOH) was proved somewhat
less accurate when the AOH exceeds 1 metre, and further analysis is required in order
to fully investigate the non-linear relationships between the examined variables and the
amended object height.

Stopping Sight Distance (SSD) is a key control element which directly affects the suggested value... more Stopping Sight Distance (SSD) is a key control element which directly affects the suggested values of crucial road design parameters. Although there is a significant difference in SSD values between upgrades and downgrades, many Design Policies ignore the grade effect during vehicle braking on variable grades. Such a case is experienced during the determination of sag vertical curvature rates where the relevant SSD values are extracted assuming leveled road geometry. The paper investigates possible deficiency of this approach, regarding cases where the length of the vertical curve exceeds the control SSD values.
The authors addressed the SSD calculation on variable grades during the braking process through a recently developed process that relates the point mass model and the laws of mechanics.
For a wide range of design speed values, charts illustrating the required SSDs were drawn as a function of negative entering grade values related to control sag vertical curve rates, as adopted by AASHTO. The process revealed numerous SSD shortage areas, where the authors provided revised sag vertical curvature rates, in order to grant SSD adequacy throughout the vehicles’ breaking process.
Furthermore, the authors aiming to provide the designers with ready-to-use vertical design tool associated the amended vertical curvature rates to AASHTO’s road functional classification, as a function of the sag vertical curve’s entering grade value.

JOURNAL OF TRANSPORT AND SHIPPING, Dec 1, 2007

Abstract. Given that several regions of Greece and Turkey have higher road accident death rates t... more Abstract. Given that several regions of Greece and Turkey have higher road accident death rates than any other European region, the objective of this research is the exploration of the underline parameters, which contribute to this phenomenon. On that purpose, road accident fatalities are co-examined with basic macroscopic parameters affecting road safety, like population and vehicle fleet and lognormal models are developed for Greece, Turkey and three selected groups of EU countries. The application of the models developed showed ...

Transportation Research Part F: Traffic Psychology and Behaviour, 2013

ABSTRACT There has been limited development of advanced rider assistance systems and on-bike info... more ABSTRACT There has been limited development of advanced rider assistance systems and on-bike information systems for powered two-wheelers (PTWs), even though research suggests that population-wide deployment of assistive systems could significantly reduce PTW crashes. This study aims to understand general and system-specific factors that are likely to influence acceptability of PTW assistive systems, including barriers that may prevent uptake and proper use of systems, through a large-scale survey of European riders. The survey was available in seven languages and attracted 6297 respondents. Respondents were frequent riders, who rode primarily for leisure purposes and had high awareness of assistive systems. Cluster analysis revealed two groups based on overall acceptability of assistive systems. The moderate and low acceptance clusters differed in terms of riding practices, risk perception, attitudes towards rule breaking, and some personality traits. Overall acceptability was low, but riders who perceive greater risk in riding display higher acceptability. Acceptability was highest for systems that do not interfere with the riding task, are well-known and/or considered reliable (e.g., night vision, ABS, eCall, advanced front-lighting system). In general, riders believe that existing safety equipment (e.g., helmets, protective clothing) is more reliable, provides greater resistance, and is considerably cheaper than more sophisticated assistive technology. Riders believe that innovations should focus on protective equipment, since they believe crash prevention is better addressed through rider training. Finally, riders felt there should be more emphasis on vehicle tyre condition, while tyre pressure control systems were identified as potentially helpful.

The objective of the present paper is to explore key parameters contributing to road safety in Be... more The objective of the present paper is to explore key parameters contributing to road safety in Belarus through the analysis of basic road safety data. In addition, road safety trends in Belarus are compared to those of EU member countries, which based on the different socioeconomic and road safety characteristicsare categorized in three distinct groups, , namely; Northwest , South and East EU members. On this purpose the latest general trends in road safety in Belarus were recorded and socioeconomic parameters were selected to explore the impact of each one of them to the number of road fatalities per population. A lognormal model was developed for Belarus and for the selected groups of EU countries. Dimensionless elasticities were used for the direct comparison of all model parameters, in order to identify differences and similarities in road safety performance in the examinedcountries. The examination of Belarus revealed findings very similar to those of East EU member countries, according to which the number of road fatalities per population was found to be affected by the GDP per capita but not by the total fleet. Specifically, an increase in the GDP per capita leads to a decrease in road fatalities per population. A negative relation between GDP per capita and road fatalities per population, although morethan double in terms of quantitative impact, was also found in the case of Northwest EU members.Contrary to the above findings, regarding South EU countries, the analysis showed that the total fleet has an impact on the number of road fatalities per population, where the GDP per capita has the adverse kind of impact on road fatalities per population than in the other examined groups. The results of this research revealed the importance of basic socioeconomic parameters on road fatalities' macroscopic trends. Common characteristics of neighbouring countries may explain similar road safety performance, and relevant findings may be exploited by all those who attempt to identify future road safety trends and propose appropriate countermeasures and policies.

Journal of Safety Research, 2007

This paper reports on the accident risk of foreign and native drivers in various road environment... more This paper reports on the accident risk of foreign and native drivers in various road environments in Greece. In particular, the analysis aims to determine the combined effect of driver nationality, area type (inside/outside urban area), junction (yes/no), and lighting conditions (day/night) on accident fault risk. Data from the national accident database of Greece are used in a hierarchical log-linear analysis. The induced exposure technique is applied due to the lack of exposure data. Estimated and observed odds ratios are then examined for the quantification of the various effects in terms of relative risk. The initial examination of a saturated model leads to the rejection of all three- and higher-order effects within variables, without providing an adequate fit to the data. On the contrary, a non-saturated second-order model presents a very satisfactory overall fit. The examination of single and combined effects indicates that the most significant effect on accident risk rises from the presence of foreign drivers at junctions. Results confirm that foreign drivers in Greece are at increased risk. However, immigrant permanent residents appear to have a lower risk compared to tourists, regardless of the road environment.

Transportation Research Record, 2007

Accident; analysis and prevention,58,340-45, 2012

Technika Chronika I,Vol3,3, 2001

International journal of injury control and safety promotion, 2007

This paper investigates the combined effect of driver nationality and several road characteristic... more This paper investigates the combined effect of driver nationality and several road characteristics (area type, at or not at junction, lighting conditions) on accident fault risk. Data from the national accident database of Greece are used to calculate accident relative fault risk rates under induced exposure assumptions. A log-linear analysis is then used to examine first- and higher-order effects within three or more variable groups. The examination of the second-order interaction among the accident fault risks of various driver nationalities at or not at junction was found to be significant. On the contrary, the respective combined effects of area type and lighting conditions were found to be non-significant. It was also shown that roadway features do not affect accident fault risk in a combined way. Results clearly indicate that foreign drivers in Greece are at increased risk. Moreover, foreign nationalities corresponding to permanent residents (i.e. Greeks and Albanians) appear to be at lower fault risk compared to foreign nationalities corresponding to tourists and visitors (e.g. EU Nationals). The effects of the various road characteristics do not modify these general trends.

Transportation Research Part F: Traffic Psychology and Behaviour 22, 86-95, 2014

Transportation Research Part F-traffic Psychology and Behaviour,Vol. 12,Issue 3, May 2009

This paper concerns a review and critical assessment of the existing research on pedestrian behav... more This paper concerns a review and critical assessment of the existing research on pedestrian behaviour in urban areas, focusing on two separate yet complementary aspects: route choice and crossing behaviour. First, an exhaustive review of the existing route choice models for pedestrians is presented. It is shown that the existing models are mainly more stochastic and more macroscopic than required and seldom incorporate the interactions between pedestrians and traffic. Second, the existing models on pedestrians crossing ...

Transport Reviews,16 (4), 357-367, 1996

This paper presents an overview of the road safety issue in Greece. First, road fatalities are in... more This paper presents an overview of the road safety issue in Greece. First, road fatalities are investigated, and their characteristics and temporal and other variations are analysed. Then the severity of accidents is presented. It is found that the most serious accident types in Greece do not include head on collisions, as expected, but collisions to fixed object or vehicle, pedestrian accidents and coming off the road. Then, a comparison of road accidents in Greece to the fourteen other EU countries is carried out. The trends show that Greece is in one of the worst positions within the EU. Greece seems also to belong to a group of countries, including South European countries and Ireland, which present road safety characteristics significantly different from those of the other EU countries. The reasons for these differences are explained in detail. Finally, the paper proceeds to a description of the safety measures already implemented in Greece, and concludes with recommendations for improving road safety in this country.

Transport reviews 22 (2), 179-196, Jan 2002

Transport Logistics, Vol. 1, No. 4, pp. 251–264, 1998

Proceedings of The Institution of Civil Engineers-transport, 2007

Résumé/Abstract Within this research the travel patterns of passenger car drivers are investigate... more Résumé/Abstract Within this research the travel patterns of passenger car drivers are investigated in relation to their age, as recorded from a national travel survey conducted in Greece. For the needs of this research drivers are classified into three mutually exclusive age groups: young (18-24), adult (25-64) and elderly (65+). The mobility of these three driver groups-expressed in terms of average annual distance driven-is then investigated with respect to parameters involving driver characteristics (experience, gender), vehicle ...

Journal of Transportation Engineering-asce, 2007

This paper presents a methodology for modeling pedestrians&amp;amp;amp;amp;amp;#x27; cros... more This paper presents a methodology for modeling pedestrians&amp;amp;amp;amp;amp;#x27; crossing behavior along an urban trip, as well as an algorithm for the estimation of accident risk along the trip. For that purpose, existing models are exploited and further developed. In particular, a nested logit model and a linear regression model are merged and adapted to develop a hierarchical crossing behavior model, allowing for the estimation of a distribution of crossing probabilities on an urban road link among junctions and various midblock locations. The explanatory ...