Suren Chen

Injury severities of truck drivers in single- and multi-vehicle accidents on rural highways

In adverse driving conditions, such as inclement weather and/or complex terrain, trucks are often involved in single-vehicle (SV) accidents in addition to multi-vehicle (MV) accidents. Ten-year accident data involving trucks on rural highway from the Highway Safety Information System (HSIS) is studied to investigate the difference in driver-injury severity between SV and MV accidents by using mixed logit models. Injury severity from SV and MV accidents involving trucks on rural highways is modeled separately and their respective critical risk factors such as driver, vehicle, temporal, roadway, environmental and accident characteristics are evaluated. It is found that there exists substantial difference between the impacts from a variety of variables on the driver-injury severity in MV and SV accidents. By conducting the injury severity study for MV and SV accidents involving trucks separately, some new or more comprehensive observations, which have not been covered in the existing studies can be made. Estimation findings indicate that the snow road surface and light traffic indicators will be better modeled as random parameters in SV and MV models respectively. As a result, the complex interactions of various variables and the nature of truck-driver injury are able to be disclosed in a better way. Based on the improved understanding on the injury severity of truck drivers from truck-involved accidents, it is expected that more rational and effective injury prevention strategy may be developed for truck drivers under different driving conditions in the future.

PARAMETRIC STUDY ON MULTIPLE TUNED MASS DAMPERS FOR BUFFETING CONTROL OF YANGPU BRIDGE

Abstract A study on buffeting control of the Yangpu Bridge using a multiple tuned mass damper (MTMD) system is performed in this paper. The MTMD system consists of a set of TMDs which are attached to the center region of the bridges main span and are symmetrical about the center of the main span as well as about the central line along the bridge span. It is found that the control efficiency of the MTMD system is sensitive to its frequency characteristics, namely, the central frequency ratio and the frequency bandwidth ratio. On the other hand, the damping ratio of the TMDs has less significant effects on the control efficiency. A total of seven MTMD systems with different mass ratios are designed. Each one of these seven MTMD systems can be used for the buffeting control of the Yangpu Bridge, depending on the required control efficiency and the available budget.

Simulation-Based Assessment of Vehicle Safety Behavior under Hazardous Driving Conditions

Future sustained economic growth of the nation very much depends on the reliability and efficiency of its highway infrastructure system. Some vehicles, such as trucks, emergency vehicles, and sport utility vehicles, often experience increasing risks of single-vehicle accidents under hazardous driving conditions, such as inclement weather and/or complicated topographical conditions. An advanced simulation-based single-vehicle accident assessment model is developed considering the coupling effects between vehicles and hazardous driving conditions, including wind gust, snow-covered or icy road surface, and/or curving. Compared to existing simulation models, the new model focuses on characterizing the transient process of accidents, introducing new critical variables on assessing the accident risks under more comprehensive hazardous driving conditions and establishing more realistic accident criteria. As a holistic deterministic model, it can be used to provide useful assessment and prevention information for traffic and emergency management. For example, it can be used to define appropriate safe driving speed limits for vulnerable vehicles under normal and extreme conditions and predict potential crash and injury risk of vulnerable drivers. Moreover, the new deterministic vehicle safety behavior simulation model lays a critical basis for future reliability-based studies of single-vehicle accident risks of vulnerable vehicles under hazardous conditions. After the model is introduced, numerical analyses on a typical truck under several representative hazardous scenarios will be conducted for demonstration purposes.

Characteristics and Dynamic Impact of Overloaded Extra Heavy Trucks on Typical Highway Bridges

AbstractOverloaded trucks, including some extra heavy trucks, often cause serious threats to bridges, such as deterioration, fatigue damage, or even collapse. Compared with the standard traffic design loads in design specifications, the actual characteristics of overloaded trucks, such as truck weight and types, are very difficult to predict or define. These characteristics are not specific only to the location. Rather, they depend on the economy, regulations, and law enforcement, and also vary over time as a result of uncertainties at a given location. In the current study, long-term traffic monitoring data are statistically studied to identify the key characteristics of extra heavy trucks, such as vehicle type, lane distribution, speed, axle weight, axle distance, and the variation of flow rate over time. All of the trucks from the traffic monitoring data are classified into 17 typical vehicle types, in which a total of 1,319 extra heavy truck scenarios are extracted from the traffic monitoring data. To...

Evolution of long-span bridge response to wind-numerical simulation and discussion

Flutter and buffeting are two important phenomena of long-span bridges susceptible to wind actions. When the wind velocity increases to the bridge flutter velocity, an initial or self-excited multi-frequency vibration in laminar flow becomes single-frequency flutter instability. Similarly, in turbulent flow, the multi-frequency buffeting vibration develops into a single-frequency dominated divergent vibration that can also be interpreted as flutter instability. Even though this transition from buffeting to flutter was observed in wind tunnel tests, the mechanism of transition from multi-frequency type of buffeting to single-frequency type of flutter has not been well demonstrated numerically. Some existent explanations on the occurrence of flutter are very generic and even somewhat confusing. An attempt to reinvestigate numerically the transition of these two phenomena was made in the present study. The established procedure demonstrates numerically how a pre-flutter multi-frequency free vibration and a multi-frequency buffeting vibration merge into a single-frequency dominated flutter at the flutter critical wind velocity. It is concluded that the modal coupling effect forces all modes to vibrate mainly in a frequency close to the oscillation frequency of the critical flutter mode. The oscillation frequency of each mode itself does not merge to that of the critical mode. As a result, some confusing concepts in flutter vibrations are clarified and the mechanisms of the vibration transition process are better understood. Numerical analyses of the Humen suspension bridge with a main span of 888 m were conducted to facilitate the discussions.

Refined-scale panel data crash rate analysis using random-effects tobit model

Random effects tobit models are developed in predicting hourly crash rates with refined-scale panel data structure in both temporal and spatial domains. The proposed models address left-censoring effects of crash rates data while accounting for unobserved heterogeneity across groups and serial correlations within group in the meantime. The utilization of panel data in both refined temporal and spatial scales (hourly record and 1-mile roadway segments on average) exhibits strong potential on capturing the nature of time-varying and spatially varying contributing variables that is usually ignored in traditional aggregated traffic accident modeling. 1-year accident data and detailed traffic, environment, road geometry and surface condition data from a segment of I-25 in Colorado are adopted to demonstrate the proposed methodology. To better understand significantly different characteristics of crashes, two separate models, one for daytime and another for nighttime, have been developed. The results show major difference in contributing factors towards crash rate between daytime and nighttime models, implying considerable needs to investigate daytime and nighttime crashes separately using refined-scale data. After the models are developed, a comprehensive review of various contributing factors is made, followed by discussions on some interesting findings.

Study on stability improvement of suspension bridge with high-sided vehicles under wind using tuned-liquid-damper

Smooth and safe traffic on the highway system is crucial for a modern society. As the backbone of a highway system, key long-span suspension bridges as well as moving high-sided vehicles on the bridges are vulnerable to strong wind. Excessive vibration of bridges and vehicles may cause the bridge aerodynamic instability and vehicle accidents. When wind is strong, the excessive torsional response of the bridge also contributes to the discomfort of drivers or the occurrence of overturning accidents of vehicles moving on it. Potentials of adopting the tuned-liquid-damper (TLD) system as an enhancement measure for the stability of suspension bridges with high-sided vehicles are evaluated. Firstly, a general shallow water sloshing model in rectangular containers under off-axle rotation, lateral and vertical excitations is developed. The analytical platform of the general 3-D bridge—vehicle—TLD system under wind and road roughness excitations is introduced. Secondly, a parametric study of the off-axle TLDs in controlling torsional motion of a simple single torsional mode bridge model under broadband white noise excitation is conducted to investigate the effectiveness and mechanism of the TLD on torsional motion. Finally, a numerical analysis of TLDs installed on a real suspension bridge—vehicle—wind system in time history is carried out considering interactions between the multimode bridge structure, multiple vehicles and the wind excitation. The results suggest that the off-axle TLD system can effectively suppress the torsional response of the suspension bridge through acting as a pendulum damper in addition to a typical sloshing damper, but has little direct suppression effect on the vibrations of vehicles.

Time-Progressive Dynamic Assessment of Abrupt Cable-Breakage Events on Cable-Stayed Bridges

AbstractAlthough long-span bridges are usually designed with sufficient structural redundancy, particular concerns arise about the abrupt breakage of bridge cables, which may cause progressive failure such as zipper-like collapse. The time-progressive nonlinear dynamic analysis approach is proposed to investigate the abrupt cable-breakage event of a cable-stayed bridge. Compared with existing studies, the proposed methodology focuses on the simulation of cable loss scenarios in a more realistic manner through incorporating stochastic moving traffic loads, dynamic bridge–vehicle interactions, and associated dynamic initial states of the abrupt cable-breakage event. Several important issues associated with the proposed simulation methodology, such as the finite-element modeling option of cable breakage, different initial states of cable breakage, nonlinearity, and traffic loads, are investigated through a prototype bridge example. Finally, the response envelopes in terms of moments and stresses along the wh...

Modeling crash rates for a mountainous highway by using refined-scale panel data

Traditional traffic safety analyses on crash frequency or crash rate usually focus on highly aggregated cross-sectional data. The adoption of aggregated data ignores the time-varying nature of some critical factors, and their effects on traffic safety may be masked through data aggregation. For mountainous highways, weather- and environment-related variables become critical as a result of complex time- and spatial-varying characteristics as well as interactions with mountainous terrain. Therefore, refined-scale models are often desired to appropriately model crash safety risks on mountainous highways and disclose the inherent crash mechanism. An advanced random parameter Tobit model with panel data (time series cross-sectional data) in refined temporal scale was developed. This is so far the first reported effort on integrating random parameter Tobit model and refined-scale panel data to develop crash rate models. A random parameter model was adopted not only to handle unobserved heterogeneity explicitly, but also to account for serial correlations across observations in panel data. Refined-scale weather and traffic data in a panel formation were adopted to accommodate the varying nature of complex driving conditions. Interstate 70 (I-70) in Colorado is well known for its typical mountainous terrain, critical role for local and national traffic, and inclement weather. As a demonstration of the modeling techniques, crash rates for a segment of I-70 were investigated in refined temporal scale. Results showed that a random parameter Tobit model outperformed a fixed-parameter Tobit model, and factors related to traffic, weather, and surface conditions were found to play significant roles in an accident rate model.

Multi-scale traffic safety and operational performance study of large trucks on mountainous interstate highway

In addition to multi-vehicle accidents, large trucks are also prone to single-vehicle accidents on the mountainous interstate highways due to the complex terrain and fast-changing weather. By integrating both historical data analysis and simulations, a multi-scale approach is developed to evaluate the traffic safety and operational performance of large trucks on mountainous interstate highways in both scales of individual vehicle as well as traffic on the whole highway. A typical mountainous highway in Colorado is studied for demonstration purposes. Firstly, the ten-year historical accident records are analyzed to identify the accident-vulnerable-locations (AVLs) and site-specific critical adverse driving conditions. Secondly, simulation-based single-vehicle assessment is performed for different driving conditions at those AVLs along the whole corridor. Finally, the cellular-automaton (CA)-based simulation is carried out to evaluate the multi-vehicle traffic safety as well as the operational performance of the traffic by considering the actual speed limits, including the differential speed limits (DSL) at some locations. It is found that the multi-scale approach can provide insightful and comprehensive observations of the highway performance, which is especially important for mountainous highways.