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Centrosomal protein dysfunction might cause ciliopathies. However, the role of centrosomal proteins in male infertility remains poorly defined. Here, we identified a pathogenic splicing mutation in

Accurately quantifying the aerodynamic forces acting on vehicles and long-span bridges is critical for assessing the safety of moving vehicles on bridges which are subjected to strong wind. It is necessary to consider the aerodynamic interference between vehicles and the bridge, especially for this with the bluff body section and wind barriers. However, very few investigations have been carried out to find aerodynamic coefficients of vehicles on a bridge with the bluff body section and considering the effect of wind barrier. This article therefore carried out wind tunnel tests to determine aerodynamic coefficients of container truck on a bridge with a π-cross section and wind barriers. The influence of vehicle position in different road lanes of the bridge deck and the aerodynamic interference between vehicles on the aerodynamic characteristics of the vehicle and the bridge are investigated. Different heights and ventilation ratios of wind barrier are taken into consideration to examine variations of aerodynamic coefficients with different wind barriers. Furthermore, the change mechanism in the aerodynamic coefficients of the vehicles is observed by analyzing the wind pressure distribution on the surface of the vehicles. The test results show that the different lane locations of the vehicle affect the aerodynamic coefficients significantly, as well as the aerodynamic interference between vehicles with transverse arrangement or longitudinal arrangement, especially for the side force coefficient. The existence of wind barrier reduces the side force coefficients of the vehicle remarkably. Such effects also vary with the ventilation ratio and height of wind barrier.

Tree failures due to strong winds in urban areas cause extensive direct and indirect economic and environmental loss, including disrupting adjacent infrastructures, such as buildings, underground pipelines, roads and overhead powerlines. To effectively improve the resilience of a community subjected to extreme wind events through prevention, response and recovery, it becomes critical to rationally assess the risks of wind-induced tree failures and the disruptions to different types of infrastructures due to fallen trees. An integrated probabilistic methodology to model the performance of disrupted infrastructures is developed for fallen urban trees subjected to extreme winds in a typical community. Firstly, the finite element modeling of the trees subjected to wind loads is conducted and based on which the windthrow fragility curves of several typical urban tree species are developed. Secondly, a probabilistic framework is developed based on the fragility results to characterize the disrupted scenarios and further predict the disruption probability of some critical infrastructures due to fallen trees. The matrix-based system reliability (MSR) method is introduced to assess the transportation network performance. The proposed framework and MSR method are demonstrated in detail on studying the overhead powerline and transportation network of a small urban community in the city of Fort Collins, Colorado. In the demonstrative example, the probabilities of powerline disruption, road closure, and origin–destination disconnection and travel time reliability under different wind conditions are predicted. Finally, mitigation efforts such as crown thinning of trees are discussed to reduce possible risks of disrupting the infrastructures.

Vehicles are extremely vulnerable to single-vehicle accidents under some hazardous driving conditions (i.e. strong wind, icy or snowy road surface). An integrated framework is proposed to assess single-vehicle traffic safety performance of stochastic traffic flow under hazardous driving conditions. Different from most existing studies focusing on a single vehicle moving at a constant speed, for the first time, the proposed work evaluates individual vehicle safety performance based on the time-dependent simulation results of stochastic traffic flow, including instantaneous speeds and positions of each vehicle as a part of simulated traffic flow. Simultaneously, complex geometric and other environmental conditions of the highway system are also considered realistically, not only during the safety assessment process, but also in quantifying the wind loads applied on the vehicles. Finally, with the safety information of each individual vehicle, an overall safety performance index of the whole traffic flow on the highway system is further introduced, which serves as a potential traffic safety performance measure and resilience indicator of transportation infrastructure systems under various hazards. This study has potential applications to not only regular vehicles, but also advanced traffic management and control algorithms for connected and autonomous vehicles in hazardous driving environments.

With many people using subways at the same time, subway stations must be appropriately designed to allow people to move smoothly and safely during daily operation and emergency evacuation. The pres...

Green stormwater infrastructure (GSI) is increasingly used to reduce stormwater input to the subsurface stormwater network. This work investigated how GSI interacts with surface runoff and stormwater structures to affect the spatial extent and distribution of roadway flooding and subsequent effects on the performance of the traffic system using a dual-drainage model. The model simulated roadway flooding using PCSWMM (Personal Computer Stormwater Management Model) in Harvard Gulch, Denver, Colorado, and was then used in a microscopic traffic simulation using the Simulation of Urban Mobility Model (SUMO). We examined the effect of converting between 1% and 5% of directly connected impervious area (DCIA) to bioretention GSI on roadway flooding. The results showed that even for 1% of DCIA converted to GSI, the extent and mean depth of roadway flooding was reduced. Increasing GSI conversion further reduced roadway flooding depth and extent, although with diminishing returns per additional percentage of DCIA converted to GSI. Reduced roadway flooding led to increased average vehicle speeds and decreased percentage of roads impacted by flooding and total travel time. We found diminishing returns in the roadway flooding reduction per additional percentage of DCIA converted to GSI. Future work will be conducted to reduce the main limitations of insufficient data for model validation. Detailed dual-drainage modeling has the potential to better predict what GSI strategies will mitigate roadway flooding.

The epigenetic inheritance relies on stability of histone marks, but various diseases, including aging-related diseases, are usually associated with alterations of histone marks. How the stability of histone marks is maintained still remains unclear. The core histones can be degraded by the atypical proteasome, which contains the proteasome activator PA200, in an acetylation-dependent manner during somatic DNA damage response and spermiogenesis. Here we show that PA200 promotes the transcription-coupled degradation of the core histones, and plays an important role in maintaining the stability of histone marks. Degradation of the histone variant H3.3, which is incorporated into chromatin during transcription, was much faster than that of its canonical form H3.1, which is incorporated during DNA replication. This degradation of the core histones could be suppressed by the transcription inhibitor, the proteasome inhibitor or deletion of PA200. The histone deacetylase inhibitor accelerated the degradation rates of H3 in general, especially its variant H3.3, while the mutations of the putative acetyl-lysine-binding region of PA200 abolished histone degradation in the G1-arrested cells, supporting that acetylation is involved in the degradation of the core histones. Deletion of PA200 dramatically altered deposition of the active transcriptional hallmarks (H3K4me3 and H3K56ac) and transcription, especially during cellular aging. Furthermore, deletion of PA200 or its yeast ortholog Blm10 accelerated cellular aging. Notably, the PA200-deficient mice displayed a range of aging-related deteriorations, including immune malfunction, anxiety-like behaviors and shorter lifespan. Thus, the proteasome activator PA200 is critical to the maintenance of the stability of histone marks during transcription and aging.

Timely rescue of injured people by emergency medical services (EMS) is essential for disrupted traffic networks due to the failures of transportation infrastructure following major hazards. Rational resilience performance indicators in terms of EMS cannot only help implementing an optimized post-disaster medical response plan, but also identify the most cost-effective pre-disaster preventive measures. A framework to assess the resilience performance of a typical traffic network in terms of post-earthquake EMS is developed by considering the interactions between building infrastructures, injured people, vulnerable medical centers, EMS vehicles, disrupted traffic network, and natural hazards. Two resilience performance indicators are introduced characterizing the relative importance of different links and overall EMS resilience for the whole network. A virtual community is selected to demonstrate the proposed framework, which is followed by a parametric study of the earthquake magnitude, bridge type...

A wind tunnel experimental study is conducted to study the wind loads acting on a moving vehicle model on a bridge installed with a solid wind barrier. The repeatability of the tests is verified by the cases with different wind and vehicle speeds. For comparison purposes, the difference of the results between the static and moving vehicle models are discussed. The effects of different heights of wind barriers and wind directions on the wind loads acting on the vehicles are analyzed. Finally, the wind loads acting on the vehicles are further evaluated to assess the potential impact of wind barriers on traffic safety. The results show that the relative movement between the vehicle, bridge and solid wind barriers affects the aerodynamic characteristics of the vehicle. The variation patterns of aerodynamic characteristics with different yaw angles are altered by the solid wind barriers with different heights, and there is a most unfavorable yaw angle for the protective effect of solid wind barriers in terms of side force. The wind direction has some impact on the five-component coefficients of vehicles after installing a solid wind barrier. However, the solid wind barrier has similar protective efficiency in terms of the side force acting on the vehicle under different wind directions.

Road traffic crashes threaten thousands of drivers every day and significant efforts have been put forth to reduce the number and mitigate the impacts of traffic crashes. Although the last decade has witnessed substantial methodological improvements in crash prediction modelling, several methodological challenges still remain in terms of predicting crash frequencies of different injury severity levels. These challenges include spatial correlation and/or heterogeneity, temporal correlation and/or heterogeneity, and correlations between crash frequencies of different injury severity level. A framework of Bayesian multivariate space-time model is developed to address these challenges. A series of multivariate space-time models are proposed under the Full Bayesian framework with different assumptions on the spatial and temporal random effects. In addition to the ability to consider both temporal and spatial trends, the proposed framework is also capable of addressing complex correlations between crash types. It allows the underlying unobserved heterogeneity to be better captured and enables borrowing strength across spatial units and time points, as well as over crash types. The proposed methodology is illustrated using one-year daily traffic crash data from the mountainous interstate highway I70 in Colorado, which is categorized into no injury crash and injury crash. The results show that multivariate space-time model outperforms other alternatives, including multivariate random effects model and multivariate spatial models. The model comparison results highlight the importance to properly account for spatial effects, temporal effects and correlations between crash types.

A typical highway system includes infrastructures, such as roadways and bridges, and moving traffic flow. The resilience of a highway system subjected to various hazards depends on not only post-hazard integrity of infrastructure, but also safe and smooth movements of vehicles through the system during and immediately following hazards. To rationally predict the post-hazard performance of a highway system including both structural integrity and traffic functionality, an advanced traffic flow simulation tool of a highway system under hazardous conditions is needed. A new cellular automaton (CA)-based traffic flow simulation framework is developed for the traffic flow simulation on a typical highway system including a long-span bridge under hazardous conditions by incorporating limited deceleration rate, anticipation effect, realistic vehicle properties, and different driving behaviors. A demonstrative study is carried out with the proposed framework to investigate the traffic flow characteristics a...

A new experimental investigation approach of a moving vehicle device is proposed to investigate the aerodynamic characteristics of moving vehicles on bridges under crosswinds. The new moving vehicle device, which can adjust the incoming wind directions and wind attack angles, consists of a vehicle, bridge segment, and motion system etc. The motion system includes a linear module propelled by a servo motor and it can realize bidirectional motions and rapid acceleration and deceleration. The five-component coefficients of the moving vehicle model were tested with the force balance equipment, and the sensitivity of some parameters on the aerodynamic characteristics of moving vehicles is studied. The results show that the proposed moving vehicle device can provide a rather smooth guideway. The measured time histories of aerodynamic force and moment are stable after filtering and the identified aerodynamic characteristics of moving vehicles have a good consistency over different wind speeds.

In the present study, a new assessment simulation of ride safety based on a new wind-traffic-pavement-bridge coupled vibration system is developed considering stochastic characteristics of traffic flow and bridge surface. Compared to existing simulation models, the new assessment simulation focuses on introducing the more realistic three-dimensional vehicle model, stochastic characteristics of traffic, vehicle accident criteria, and bridge surface conditions. A three-dimensional vehicle model with 24 degrees-of-freedoms (DOFs) is presented. A cellular automaton (CA) model and the surface roughness are introduced. The bridge deck pavement is modeled as a boundless Euler-Bernoulli beam supported on the Kelvin model. The wind-traffic-pavement-bridge coupled equations are established by combining the equations of both the vehicles in traffic, pavement, and bridge using the displacement and interaction force relationship at the patch contact. The numerical simulation shows that the proposed method can simulate rationally useful assessment and prevention information for traffic, and define appropriate safe driving speed limits for vulnerable vehicles under normal traffic and bridge surface conditions.

Work zone traffic safety under adverse weather conditions has been a serious concern for drivers and transportation agencies. Existing studies on work zone traffic safety with statistical approaches are limited by the availability of data from historical crashes. To date, there is no comprehensive simulation framework to assess work zone traffic safety under adverse driving environments by considering both multi-vehicle and single-vehicle crashes. To fill this gap, this paper presents an integrated framework to evaluate traffic safety in work zone under adverse driving conditions by considering specific work zone configuration, weather and road surface conditions. A new risk index is introduced to assess the traffic safety risk of work zones by integrating the risks of multi-vehicle crashes and single-vehicle crashes. Traffic safety of a typical work zone under different weather conditions is studied to demonstrate the proposed framework. The impacts of the differential speed limits (DSL) and truck proportion on the work zone traffic safety are also investigated. Results show that adverse weather may increase the crash risk in work zones. The effect of DSL on the work zone traffic safety is found to be insignificant while the truck ratio influences the work zone safety in the rainy and snowy weather by primarily affecting the multi-vehicle crash risks.

Owing to current limitations on seismic forecasting, there is a high chance that a considerable number of vehicles will remain on bridges when an earthquake occurs. In traditional seismic a...

The interaction between germ cell and somatic cell plays important roles in germ cell development. However, the exact function of gonad somatic cell in germ cell differentiation is unclear. In the present study, the function of gonad somatic cell in germ cell meiosis was examined by using mouse models with aberrant somatic cell differentiation. In Wt1R394W/R394W mice, the genital ridge is absent due to the apoptosis of coelomic epithelial cells. Interestingly, in both male and female Wt1R394W/R394W germ cells, STRA8 was detected at E12.5 and the scattered SYCP3 foci were observed at E13.5 which was consistent with control females. In Wt1-/flox; Cre-ERTM mice, Wt1 was inactivated by the injection of tamoxifen at E9.5 and the differentiation of Sertoli and granulosa cells was completely blocked. We found that most germ cells were located outside of genital ridge after Wt1 inactivation. STRA8, SYCP3, and γH2AX proteins were detected in germ cells of both male and female Wt1-/flox; Cre-ERTM gonads, whereas no thread-like SYCP3 signal was observed. Our study demonstrates that aberrant development of gonad somatic cells leads to ectopic expression of meiosis-associated genes in germ cells, but meiosis was arrested before prophase I. These results suggest that the proper differentiation of gonad somatic cells is essential for germ cell meiosis.

Posthazard traffic networks are often disrupted, not only because of direct impacts on transportation infrastructure but also because of indirect impacts originating from the interdependent...

It is important from the safety and economical perspectives that a suspension bridge should have minimal deformation under the self-weight of the bridge while the tension forces of the main...

Vehicle ride comfort issues for the drivers are related to not only individual satisfaction of driving experience, but also driving safety and long-term health of the drivers. A new methodology of ride comfort analysis is presented for typical vehicles driven on long-span bridges considering realistic traffic and environmental loads such as wind excitations. Built on the simulation framework developed previously by the writers, complex interactions among the long-span bridge, all the vehicles in the traffic flow and wind excitations are appropriately modeled. Vehicle ride comfort condition is evaluated by extending the advanced procedures as currently recommended in the ISO 2631-1 standard to the scenarios of multiple vehicles in the stochastic traffic flow, including obtaining the whole-body vibration response, frequency weighting the original response and determining the Overall Vibration Total Value (OVTV). The proposed methodology is then applied to a prototype long-span cable-stayed bridge and traffic system to demonstrate the proposed ride comfort evaluation methodology. The study starts with the baseline scenario when the vehicles are driven on the rigid road without considering the interactions with the supporting structure and wind excitations, followed by the scenarios of vehicles driven on the bridge. The influences of dynamic interactions, presence of other vehicles and wind excitations on the ride comfort are also numerically evaluated.

Reinforced concrete (RC) bridges with both skew and curvature are pretty common in areas with complex terrains. Existing studies have shown skewed and/or curved bridges exhibit more complicated seismic performance than straight bridges, and yet related seismic risk studies are still rare. These bridges deserve more studies in low-to-moderate seismic regions than those in seismic-prone areas. This is because for bridges with irregular and complex geometric designs, comprehensive seismic analysis is not always required and little knowledge about actual seismic risks for these bridges in low-to-moderate regions is available. To provide more insightful understanding of the seismic risks and the impact from the geometric configurations, analytical fragility studies are carried out on four typical bridge designs with different geometric configurations (i.e., straight, curved, skewed, skewed and curved) in the mountain west region of the United States. The results show the curved and skewed geometries can considerably affect the bridge seismic fragility in a complex manner, underscoring the importance of conducting detailed seismic risk assessment of skewed and curved bridges in low-to-moderate seismic regions.

Accidents, such as deflections, side slips, and even rolls, can easily occur when road vehicles moving on the bridge deck at high speed are subjected to sudden changes owing to strong crosswinds. Wind barriers are an effective way to ensure the driving safety of vehicles on the bridge but with potential negative influences on the aerodynamic performance. Therefore, it is critical to evaluate the shielding effect of wind barriers on road vehicles by assessing the overall impact on the vehicle–bridge system. To optimize the wind-barrier scheme, a series of wind tunnel tests is conducted to evaluate the effects of barrier parameters on the aerodynamic characteristics of the wind-vehicle-bridge system. In this study, the aerodynamic force coefficients of the wind–vehicle–bridge system installed with wind barriers with four different heights and three ventilation ratios were investigated. With wind barriers installed on the bridge deck, dynamic responses of the wind–vehicle–bridge system were simulated with the proposed prediction procedures as those used in an earlier study. Results show that wind barriers on the bridge deck have significant influences on the aerodynamic force coefficients of the bridge, especially on the side-force coefficients, and on the dynamic responses of the wind–vehicle–bridge system. Additionally, the increase of the barrier height and the decrease of the barrier ventilation ratio considerably increase and decrease the lateral and torsional displacements of the bridge and the vehicles, respectively, but with only minor influence on the vertical displacements of both bridges and vehicles. Therefore, it is necessary to include the wind barrier in both experimental and numerical simulations of the wind-road vehicle-bridge system to explore the effect of different barrier parameters on the wind-vehicle-bridge system.

Different from short-span girder bridges, long-span bridges support a large amount of traffic, which significantly influences the dynamic performance of the bridge. The design live load on ...

This paper presents an efficient approach for dynamic stress analysis of a long-span bridge under the combined action of stochastic traffic and wind loads based on the stress influence func...

Crash rate data are mainly analyzed using the Tobit model. However, there are three major limitations associated with the Tobit model when it is applied to crash data: (1) the assumption th...

Cable breakage (loss) events can be disastrous to cable-stayed bridges because of potential risks of progressive collapse following the initial failure of stay cables. To avoid turning a cable-breakage hazard into a disaster, it is important to rationally assess the risk through accurately predicting the nonlinear dynamic behavior of the bridge subjected to various types of cable-loss events. With a recently developed advanced finite element (FE)-based nonlinear dynamic simulation platform, a comprehensive numerical investigation of cable-loss incidents on a long-span cable-stayed bridge is conducted by focusing on post-breakage performance. Parametric studies are carried out to evaluate the impacts from various important parameters related to cable-breakage process and service loads from stochastic traffic and wind. Several parameters associated with cable-breakage processes, such as the breakage duration, time-transient curve and initial state, are found to influence the dynamic performance of the bridge notably. The results also indicate that service traffic and wind loads as well as complex coupling effects with the bridge are important to the bridge response following cable-loss events. In the final part of the study, response envelope analysis is made and a comparative investigation is also conducted between the results from the advanced FE-based nonlinear dynamic approach and those from the equivalent static approach as suggested by the Post-Tensioning Institute (PTI).

Rational representation of seismic demand based on realistic characterization of earthquake ground motion is essential for seismic bridge design. Realization of the impact of vertical ground motion has led to an initiative to better characterize and simulate the seismic scenario for typical bridges in near-fault regions, such that structural design practices may improve. Current structural design provisions either do not account for effects of vertical ground motion or specify a simplistic equivalent-static-load based methodology. An assessment of the effect of vertical ground motions on a horizontally skewed and curved highway bridge is presented for a moderate-to-high seismic region. A numerical model of a skewed and curved, three-span bridge located in Tacoma, Washington is subjected to a suite of horizontal and vertical ground motions using non-linear time-history analysis. The ground motions selected are composed of a range of near-fault earthquake records with varying component characteristics such as site condition, fault distance, and vertical-to-horizontal acceleration ratios. The scenario represents a bridge with a short vibrational period in a moderate seismic zone where vertical ground motion effects may be applicable, yet are not considered by structural codes. The results of the numerical simulations depict a considerable impact from vertical ground motion to the substructure and superstructure, including behavior typically not documented in existing studies. The numerical simulations show amplification from the vertical component of ground motion in the demand on components of the substructure, particularly for vertical-to-horizontal peak ground accelerations exceeding one. The effects of vertical ground motion on skewed and curved bridges are also evaluated against a straight counterpart with comparable overall configuration. For structural designers, the results of this study indicate that excluding the vertical ground motion component from analyses may impose a larger margin of risk than previously perceived. This is particularly the case for moderate-to-high seismic regions where shorter period bridges may resonate with predominant frequencies of vertical ground motion.

High-sided vehicles often experience considerable single-vehicle accident risks under crosswinds. Long-span cable-supported bridges are usually flexible, wind-sensitive and support considerable amount of vehicles on a daily basis. When vehicles are driven through a long-span bridge, the complex dynamic interactions among wind, vehicles and the bridge significantly affect not only the safety of the bridge members, but also passing vehicles. Therefore, realistic modeling of the bridge–traffic system by characterizing these critical coupling effects becomes essential for rationally assessing traffic safety of passing traffic through a long-span bridge. In most existing studies about traffic safety study on bridges, vehicle safety was assessed for only one single vehicle or uniformly distributed vehicles at a constant driving speed. It is known that the traffic flow on a long-span bridge is typically stochastic and vehicle speeds vary following some traffic rules. Based on the stochastic traffic flow simulation, two new analytical frameworks, one using mode superposition and the other using the finite element (FE) formulation, were proposed recently for the bridge–stochastic traffic system. By considering the full-coupling effects among all the vehicles of the traffic flow, bridge and wind, the dynamic response of each individual vehicle of the stochastic traffic can be accurately obtained for the first time. Built based on the recent advances made by the authors, an integrated dynamic interaction and safety assessment model of the fully-coupled bridge–traffic system is further developed without considering vehicle aerodynamic interference and shielding effects. Traffic safety of vehicles in the stochastic traffic through the prototype long-span cable-stayed bridge is investigated as a demonstration.

Long-span cable-stayed bridges exhibit some features which are more critical than typical long span bridges such as geometric and aerodynamic nonlinearities, higher probability of the presence of multiple vehicles on the bridge, and more significant influence of wind loads acting on the ultra high pylon and super long cables. A three-dimensional nonlinear fully-coupled analytical model is developed in this study to improve the dynamic performance prediction of long cable-stayed bridges under combined traffic and wind loads. The modified spectral representation method is introduced to simulate the fluctuating wind field of all the components of the whole bridge simultaneously with high accuracy and efficiency. Then, the aerostatic and aerodynamic wind forces acting on the whole bridge including the bridge deck, pylon, cables and even piers are all derived. The cellular automation method is applied to simulate the stochastic traffic flow which can reflect the real traffic properties on the long span bridge such as lane changing, acceleration, or deceleration. The dynamic interaction between vehicles and the bridge depends on both the geometrical and mechanical relationships between the wheels of vehicles and the contact points on the bridge deck. Nonlinear properties such as geometric nonlinearity and aerodynamic nonlinearity are fully considered. The equations of motion of the coupled wind-traffic-bridge system are derived and solved with a nonlinear separate iteration method which can considerably improve the calculation efficiency. A long cable-stayed bridge, Sutong Bridge across the Yangze River in China, is selected as a numerical example to demonstrate the dynamic interaction of the coupled system. The influences of the whole bridge wind field as well as the geometric and aerodynamic nonlinearities on the responses of the wind-traffic-bridge system are discussed.

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.