| 1. |
- Othman, Sarbaz Najib, 1971, et al.
(författare)
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Are driving and overtaking on right curves more dangerous than on left curves?
- 2010
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Ingår i: Annals of advances in automotive medicine. - : Association for the Advancement of Automotive Medicine. - 1943-2461. ; 54, s. 253-264, s. 253-264
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Tidskriftsartikel (refereegranskat)abstract
- It is well known that crashes on horizontal curves are a cause for concern in all countries due to the frequency and severity of crashes at curves compared to road tangents. A recent study of crashes in western Sweden reported a higher rate of crashes in right curves than left curves. To further understand this result, this paper reports the results of novel analyses of the responses of vehicles and drivers during negotiating and overtaking maneuvers on curves for right hand traffic. The overall objectives of the study were to find road parameters for curves that affect vehicle dynamic responses, to analyze these responses during overtaking maneuvers on curves, and to link the results with driver behavior for different curve directions. The studied road features were speed, super-elevation, radius and friction including their interactions, while the analyzed vehicle dynamic factors were lateral acceleration and yaw angular velocity. A simulation program, PC-Crash, has been used to simulate road parameters and vehicle response interaction in curves. Overtaking maneuvers have been simulated for all road feature combinations in a total of 108 runs. Analysis of variances (ANOVA) was performed, using two sided randomized block design, to find differences in vehicle responses for the curve parameters. To study driver response, a field test using an instrumented vehicle and 32 participants was reviewed as it contained longitudinal speed and acceleration data for analysis. The simulation results showed that road features affect overtaking performance in right and left curves differently. Overtaking on right curves was sensitive to radius and the interaction of radius with road condition; while overtaking on left curves was more sensitive to super-elevation. Comparisons of lateral acceleration and yaw angular velocity during these maneuvers showed different vehicle response configurations depending on curve direction and maneuver path. The field test experiments also showed that drivers behave differently depending on the curve direction where both speed and acceleration were higher on right than left curves. The implication of this study is that curve direction should be taken into consideration to a greater extent when designing and redesigning curves. It appears that the driver and the vehicle are influenced by different infrastructure factors depending on the curve direction. In addition, the results suggest that the vehicle dynamics response alone cannot explain the higher crash risk in right curves. Further studies of the links between driver, vehicle, and highway characteristics are needed, such as naturalistic driving studies, to identify the key safety indicators for highway safety.
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| 2. |
- Othman, Sarbaz Najib, 1971, et al.
(författare)
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Identifying Critical Road Geometry Parameters Affecting Crash Rate and Crash Type
- 2009
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Ingår i: Association for the Advancement of Automotive Medicine (AAAM), 53rd Annual Meeting - October 4-7, 2009 - Baltimore. ; , s. 155-165
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Konferensbidrag (refereegranskat)abstract
- The objective of this traffic safety investigation was to find critical road parameters affecting crash rate (CR). The study was based on crash and road maintenance data from Western Sweden. More than 3000 crashes, reported from 2000 to 2005 on median-separated roads, were collected and combined with road geometric and surface data. The statistical analysis showed variations in CR when road elements changed confirming that road characteristics affect CR. The findings indicated that large radii right-turn curves were more dangerous than left curves, in particular, during lane changing manoeuvres. However sharper curves are more dangerous in both left and right curves. Moreover, motorway carriageways with no or limited shoulders have the highest CR when compared to other carriageway widths, while one lane carriageway sections on 2+1 roads were the safest. Road surface results showed that both wheel rut depth and road roughness have negative impacts on traffic safety. Keywords: Traffic Safety, Crash Analysis, Road geometry, Road Surface, Curve safety, Crash Data.
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| 3. |
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| 4. |
- Othman, Sarbaz Najib, 1971
(författare)
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Influence Of Road Feature Variables On Accident Rate
- 2008
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The main objective of this traffic safety investigation was to find critical road parameters affecting accident rate (AR). The secondary objective was to analyze any identified risk factors from a vehicle dynamics perspective. A better understanding of how road infrastructure affects safety can be used to predict future safety issues as well as provide guidance in selecting countermeasures when problems are identified. The study was based on accident and road maintenance data in Western Sweden. A total of 2912 accidents reported from 2000 to 2005 on 810 km median-separated roads were collected and combined with the road characteristics: reference speed, carriageway width, vertical and horizontal curves, super-elevation and road surface conditions. Factors that influence accidents have been studied through analysis of vehicle dynamics using the simulation program PC-Crash. The statistical analysis showed that the approach was sufficient for defining critical road parameters. Results showed variations in AR when road geometrical parameters changed and indicate that road characteristics have a significant effect on AR. In particular, a marked increase in AR was observed for decreasing curve radii and higher ARs were observed in right curves. Moreover, results of investigating the influence of various geometric features of curves on specific crash types showed that overtaking accidents are more frequent on right-turn curves than on left curves. Computer simulations with identical lane changing conditions showed both larger accelerations and yaw velocities in left curves than right curves. This reduces the likelihood that vehicle dynamics behaviour alone is behind the difference observed for overtaking accidents. The study also showed adverse effects of poor road surface parameters, such as wheel rut depth and road roughness (IRI), on AR. In addition, roads designed for high speed limit exhibited lower AR, but higher injury severity rates. The investigation approach and results reported in this thesis are useful input for road design guidelines and active safety systems such as ABS and ESC that are sensitive to the road characteristics. More importantly, there is a need increase the dialog between road engineers and vehicle designers in terms of traffic safety. In particular, gradual changes in vehicle characteristics over time do not seem to be reflected in changes in road design standards. For instance, improved road handling can lead to higher operating speeds than intended by road engineers. Therefore, an understanding of the higher operating speeds on specific road safety issues is useful. Similar examples apply for other vehicle-infrastructure interactions.
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| 5. |
- Othman, Sarbaz Najib, 1971, et al.
(författare)
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Safety Analysis of Horizontal Curves Using Real Traffic Data
- 2014
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Ingår i: Journal of Transportation Engineering. - : American Society of Civil Engineers (ASCE). - 0733-947X .- 1943-5436. ; 140:4
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Tidskriftsartikel (refereegranskat)abstract
- Researchers are still seeking a better understanding of the parameters that affect safety in horizontal curves. Curves are one of the most critical sections of the road network contributing to a high percentage of serious runoff accidents and lane-changing crashes. Moreover, driving in curves requires combined control of both steering and speed, taking into account the dynamic response and limits of the car. The objectives of this study were to evaluate the safety performance of horizontal curves by analyzing vehicle dynamic signals, such as lateral acceleration and speed, as well as quantitative analysis of lane-changing maneuvers. The study uses real traffic environments where driver behavior and vehicle response data were recorded and stored during regular operations without subjecting the driver to any experimental controls. A total of 96 curves, equally distributed for left and right turn directions, have been collected and grouped according to their radii. The analysis identified frequent overtaking and lane-change maneuvers on the curves, of which 20% more lane changes occurred on right curves than on left curves. Lane-change maneuvers also increased significantly with increasing curve radius. The curve entrance was found to be the most dangerous segment of a curve. Current design practice assumes the safety risk is constant when driving along horizontal curves. The results also showed that drivers consider curve radius in choosing their driving speed rather than the posted speed limit of the curves. The study showed how road design influences the driver's strategy by establishing links between curve features, vehicle dynamic responses, and the driver's behavior. Analyzing road characteristics gave insight into how road geometry affects the vehicle dynamics relevant to safety and driving strategy through curves. The findings are useful inputs for reviewing curve design, selecting appropriate countermeasures, and improving active safety devices.
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| 6. |
- Othman, Sarbaz Najib, 1971
(författare)
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Safety Evaluation of Road Characteristics
- 2011
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Accidents are rare and widely distributed on the road network, which poses a challenge for road safety improvement. Traditional methods alone, such as accident analyses and experimental studies, do not explain all accident causation factors. Traditional methods are well-established and are still important for specific contexts of road safety analyses. The objective of this doctoral thesis is to obtain an improved understanding and a safety evaluation of road features, in particular horizontal curves on non-residential roads. To explain the tendency of curves to trigger accidents is also another goal. It is essential to better understand interactions between vehicle, road, and driver components in a system which can explain possible mechanisms underlying accidents. The overall methodology of the proposed system includes the development, implementation, and integration of complementary research approaches. The approaches are based on different kinds of data sources that together produce more detailed results. In the methodology, accident and simulation analyses provided a framework for combining road, vehicle, and human behavior data collected from Field Operational Tests (FOT). The accident analysis in the system identified a set of Critical Road Parameters (CRP) with associated accident types. PC-Crash was used to simulate the influence of CRPs on vehicle response during overtaking maneuvers in curves. The CRPs and vehicle-road interaction results were used as a platform for devising a tool that could identify horizontal curve components and lane change maneuvers from FOT data. The accident analysis found more frequent overtaking crashes on right (inner) than on left (outer) curves. The simulations of road-vehicle interaction showed that the risk of a lane changing maneuver differed in curves, depending on curve direction and the lane to which the maneuver occurs. The simulations showed that requirements for drivers to remain safely within the road boundaries are greater if there is a lane changing maneuver in the curve. Despite this risk, the FOT analysis observed frequent overtaking and lane change maneuvers on the curves, of which 20% more lane changes occurred on right curves than on left curves. The curve entrance was found to be the most dangerous segment of a curve. Current design practice assumes the safety risk is constant when driving along horizontal curves. The results also showed that drivers consider curve radius in choosing their driving speed rather than the posted speed limit of the curves. The use of different data sources and approaches started with an open-ended analysis of accident data, as the first layer in a top-down process, and proceeded to the more specific and important findings of road curves. The system approach in the thesis made possible a safety tool whereby the empirical and simulation analyses together yielded more innovative and detailed results. Road feature analysis gave insight into how road geometry factors affect vehicle motion relevant to safety and driving strategy through curves. The findings are useful inputs for applications such as curve design reviews, selection of appropriate countermeasures, and the improvement of active safety devices.
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| 7. |
- Othman, Sarbaz Najib, 1971, et al.
(författare)
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Using Naturalistic Field Operational Test Data to Identify Horizontal Curves
- 2012
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Ingår i: Journal of Transportation Engineering. - : American Society of Civil Engineers (ASCE). - 0733-947X .- 1943-5436. ; 138:9, s. 1151-1160
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Tidskriftsartikel (refereegranskat)abstract
- Investigations to identify relationships between crashes and road features usually deal with effects of only one or two of the main components of traffic safety, i.e., human, vehicle, and infrastructure performance. There are several contributing factors of the components that together lead to a crash. This study devises an approach to include information from all three components in a system using field operational test (FOT) data. FOT data are recorded from real-life driving that is different from traffic simulations and specific on-site data collection. The study focuses on identifying horizontal curves using FOT and provides access to vehicle and human response data at the exact time when the vehicle drove in a specific location. A method has been developed to derive path radius and to identify start-end points of horizontal curves using FOT data. With this information, vehicle response signals and human behavior data can then be arranged on a common axis referenced to the curve. The approach also identifies lane changing maneuvers on curves that can be used to evaluate potential crash triggers. The application of this method allows for reviewing changes in the regulatory speed limit, curve geometry, or crash history and thus evaluates the design of curves and choosing appropriate countermeasures.
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