Scholarly Work - Civil Engineering

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Passenger car equivalents for heavy vehicles at freeways & multilane highways: some critical issues
(Institute of Transportation Engineers, 2006-03) Al-Kaisy, Ahmed
One of the important issues affecting the accuracy of traffic analyses is heterogeneity in the vehicular traffic mix that composes a traffic stream. Typically, the majority of vehicles in a traffic stream are passenger cars or vehicles that are similar to passenger cars in physical characteristics and performance, such as sport utility vehicles, pick-up trucks and minivans. Heavy vehicles, which usually constitute the remaining smaller proportion of a traffic mix, are larger in dimension and often inferior to passenger cars in performance. Heavy vehicles consist mainly of trucks used in freight transportation, larger buses and recreational vehicles. Despite being the smaller proportion of vehicular traffic, heavy vehicles are known for their important impacts on the traffic stream. Historically, the effect of heavy vehicles on traffic flow has been accounted for through the use of passenger car equivalency factors. These factors are intended to approximate the effect of heavy vehicles and are expressed as multiples (of the effect) of an average passenger car. In the United States, the Highway Capacity Manual (HCM) provides passenger car equivalents (PCEs) for use in capacity and level of service (LOS) analyses. Using PCEs, a heterogeneous mix of vehicles in a traffic stream can be expressed in a standardized unit of traffic, such as passenger car. PCEs are considered essential in carrying out most traffic analyses.
Static warning signs of occasional hazards: do they work?
(Institute of Transportation Engineers, 2008-06) Al-Kaisy, Ahmed; Hardy, Amanda; Nemfakos, Charles
Highway agencies expend significant resources on the installation, upgrading and maintenance of traffic control devices. To ascertain that those resources are well invested, it is important to know whether traffic control devices serve their intended purpose. The answer may be easy for some traffic control devices such as traffic signals, regulatory signs and guide signs, but it may be more difficult for other devices such as warning signs in general and those intended for occasional hazards in particular. Examples of these occasional hazards are railroad crossings, icy bridges, unexpected alignment and/or geometry, falling rocks, wildlife crossings, etc. For regulatory and guide signs, drivers feel an “obligation” to use the information provided by those signs; in the case of warning signs, the use of information and drivers’ reactions seem to be based more on perception of risk. The effectiveness of static warning signs for occasional hazards is questionable because those signs typically are posted with out the hazard being perceived by drivers. Subsequently, highway agencies have begun to question the feasibility of expending significant resources on the installation and maintenance of these signs when little evidence exists regarding their effectiveness in improving highway safety. Knowing the effectiveness of these signs in improving safety is important for highway agencies to assess the feasibility of using conventional signs and whether alternative warning devices are required for a safer highway environment.
Empirical examination of passing lane operational benefits on rural two-lane highways
(North Dakota University : Upper Great Plains Transportation Institute, 2010) Al-Kaisy, Ahmed; Freedman, Zachary Sebastian
This paper presents an empirical investigation into the operational benefits of passing lanes on rural two-lane highways. Two study sites in the state of Montana were used in this investigation. Performance was examined at a single location upstream and multiple locations downstream of the passing lane at each study site. Using percent followers as a performance measure, operational benefits right after the passing lane ranged between 33% and 42% at one study site and 12% to 19% at the other study site under prevalent traffic levels. Study results also suggest that operational benefits persist for a remarkable distance beyond the end of the passing lane.
Using hyperspectral plant signatures for CO2 leak detection during the 2008 ZERT CO2 sequestration field experiment in Bozeman, MT
(2010-03) Male, Erin J.; Pickles, William L.; Silver, Eli A.; Hoffmann, Gary D.; Lewicki, Jennifer; Apple, Martha E.; Repasky, Kevin S.; Burton, Elizabeth A.
Hyperspectral plant signatures can be used as a short-term, as well as long-term (100-year timescale) monitoring technique to verify that CO2 sequestration fields have not been compromised. An influx of CO2 gas into the soil can stress vegetation, which causes changes in the visible to near-infrared reflectance spectral signature of the vegetation. For 29 days, beginning on July 9, 2008, pure carbon dioxide gas was released through a 100-m long horizontal injection well, at a flow rate of 300 kg day−1. Spectral signatures were recorded almost daily from an unmown patch of plants over the injection with a “FieldSpec Pro” spectrometer by Analytical Spectral Devices, Inc. Measurements were taken both inside and outside of the CO2 leak zone to normalize observations for other environmental factors affecting the plants. Four to five days after the injection began, stress was observed in the spectral signatures of plants within 1 m of the well. After approximately 10 days, moderate to high amounts of stress were measured out to 2.5 m from the well. This spatial distribution corresponded to areas of high CO2 flux from the injection. Airborne hyperspectral imagery, acquired by Resonon, Inc. of Bozeman, MT using their hyperspectral camera, also showed the same pattern of plant stress. Spectral signatures of the plants were also compared to the CO2 concentrations in the soil, which indicated that the lower limit of soil CO2 needed to stress vegetation is between 4 and 8% by volume.
Channelized right-turn lanes at signalized intersections: the U.S. experience
(Aracne Editrice, 2012) Al-Kaisy, Ahmed; Roefaro, Sommer Ann
This paper presents an investigation into the current U.S. practice regarding the use of channelized right-turn lanes at signalized intersections, the type of traffic control used, and the safety experience of highway agencies. The study involved a literature review and a practice survey, which was distributed to all state and selected local agencies in the United States. The literature review revealed the overall lack of knowledge about the operational and safety aspects of channelized right-turn lanes explaining, to a large extent, the lack of guidance in practice. Survey results suggest a heavy reliance on engineering judgment by highway agencies in the use of channelized right-turn lanes and the selection of traffic control. Further, results confirmed a general perception in practice about the safety benefits of signal control at channelized right-turn lanes, despite the fact that such benefits were not supported by studies or statistics. The study emphasized the need for further research on the operational and safety aspects of this right-turn treatment at intersections.
Practical Guidelines for Estimation of Rest Area Use on Rural Interstates and Arterial Highways
(2012-01) Al-Kaisy, Ahmed; Veneziano, David; Kirkemo, Zachary S.; Dorrington, Christopher
Rest areas perform a critical role in the highway network. These areas provide passenger vehicle occupants and heavy vehicle operators with an opportunity to use a restroom, walk around, stop for a meal, sleep for a period of time, or even pause to use a cellular phone. These activities also have a direct impact on the various aspects of rest area planning and design. Existing guidance for rest area planning and design is largely based on national trends, which may not represent patterns of use in rural states. This paper presents a series of practical guidelines that may be used in the design and rehabilitation of rest area facilities, particularly those in rural areas. The guidance was developed by the use of empirical observations of rest area use at 44 study sites in the state of Montana. Given the amount of data collected and used in this research, it is reasonable to expect that the guidelines developed are representative of a significant proportion of existing and future rest area sites in rural locales. However, each rest area is different, and careful consideration should be given when the guidelines outlined in this paper are used.
Investigation of performance and lane utilization within a passing lane on a two-lane rural highway
(Scientific & Academic Publishing Co., 2013) Al-Kaisy, Ahmed; Freedman, Zachary Sebastian
An investigation into platooning and passing maneuvers within a passing lane section on a rural two-lane, two-way highway was considered in this study. The study site was located on US Highway 287 between the town of Townsend and the City of Helena in the state of Montana. Traffic volumes at study site, while considered relatively low, were typical on two-lane highways in many rural states. Per-lane analysis of performance measures and lane utilization (volume split) were used to indirectly examine passing maneuvers and lane changing at successive locations within the passing lane section. For the case study site, it was evident that traffic performance became relatively stable beyond half a mile into the passing lane for the traffic volumes investigated. Therefore, results strongly suggested that most passing maneuvers already took place before the 0.5-mile station and that the actual passing lane length was well beyond the optimal length required for breaking up platoons and improving performance.
Speed selection at sites with restrictive alignment: the US-191 case study
(2013) Al-Kaisy, Ahmed; Krieder, T.; Pothering, R.
An investigation into the driver’s choice of speed at roadway sites with restrictive alignment is presented in this study. Specifically, the study focused on the effect of horizontal curve radii and sight distance on speed selection. Seven sites were examined in this study that are located along a 10-mile stretch of a rural high crash corridor, US 191 north of Big Sky in southwest Montana. Two of the study sites have no restrictive geometry representing base conditions, another two have restrictive curve radii, and the other three have restrictive radii and sight distances. Vehicle speeds, classification, and headways were collected at each site. The selected speeds for free-moving vehicles were compared to the legal speed limit, advisory speed, and the speeds dictated by curve radius and sight distance when applicable. Study results found that the vast majority of observed selected speeds are notably higher than the speeds found using the alignment and sight distance design equations. Results also showed that the perceived safe speeds selected by drivers are likely to be determined by the most restrictive geometric feature.
Remote Sensing of Weather and Road Surface Conditions
(2013-01) Ewan, Levi A.; Al-Kaisy, Ahmed; Veneziano, David
Advances in road weather sensing technologies have made noninvasive road weather sensors a valuable component in many intelligent transportation systems (ITS) applications. This study investigates the reliability of using such a sensor for a proposed weather-responsive variable speed limit system. The Vaisala surface state and temperature sensors (DSC-111 and DST-111) were selected for the proposed application. The sensors' ability to provide accurate and reliable data was tested under various conditions in a controlled laboratory environment. Specifically, four outputs of interest from the sensors were tested in this investigation: surface state, snow and ice depth, water depth, and grip level. Testing results showed that the sensors determined the surface state (dry, moist, wet, snowy, and icy) accurately and reliably. The sensors' snow depth readings were found to be inaccurate, while the sensors' ice depth measurements were found to be relatively close to the actual depths. For water depth, only a limited number of readings were close to the actual depths, while other readings were highly inaccurate. In an effort to test the potential of the sensor in providing reliable inputs to the proposed ITS application, a calibration was conducted for the sensor water depth measurements at various water depths and sensor installation angles. Calibration results showed that the water depth could be accurately estimated with the calibrated sensor measurements, regardless of water depth or sensor installation angle. Sensor estimates of grip level were found to be highly correlated to the coefficient of static friction for the conditions considered in this study.
The Impact of Weight Matrices on Parameter Estimation & Inference: A Case Study of Binary Response Using Land Use Data
(2013-11) Wang, Yiyi; Kockelman, Kara M.; Wang, Xiaokun (Cara)
This paper develops two new models and evaluates the impact of using different weight matrices on parameter estimates and inference in three distinct spatial specifications for discrete response. These specifications rely on a conventional, sparse, inverse-distance weight matrix for a spatial auto-regressive probit (SARP), a spatial autoregressive approach where the weight matrix includes an endogenous distance-decay parameter (SARPα), and a matrix exponential spatial specification for probit (MESSP). These are applied in a binary choice setting using both simulated data and parcel-level land-use data. Parameters of all models are estimated using Bayesian methods. In simulated tests, adding a distance-decay parameter term to the spatial weight matrix improved the quality of estimation and inference, as reflected by a lower deviance information criteriaon (DIC) value, but the added sampling loop required to estimate the distance-decay parameter substantially increased computing times. In contrast, the MESSP model’s obvious advantage is its fast computing time, thanks to elimination of a log-determinant calculation for the weight matrix. In the model tests using actual land-use data, the MESSP approach emerged as the clear winner, in terms of fit and computing times. Results from all three models offer consistent interpretation of parameter estimates, with locations farther away from the regional central business district (CBD) and closer to roadways being more prone to (mostly residential) development (as expected). Again, the MESSP model offered the greatest computing-time savings benefits, but all three specifications yielded similar marginal effects estimates, showing how a focus on the spatial interactions and net (direct plus indirect) effects across observational units is more important than a focus on slope-parameter estimates when properly analyzing spatial data.
Examining the Effect of Speed and Roadway Geometry on Crash Experience along a Rural Corridor
(2014-03) Watson, Donald C.; Al-Kaisy, Ahmed; Anderson, Nathan D.
This paper presents a current investigation into crash experience along a 15.7-mile rural corridor in southwest Montana with the aim of better understanding crash causal factors along the corridor. The study utilized ten years of crash data, geometric data, and observed free-flow speed data along the corridor. A systematic approach was used where every tenth of a mile was described in term of the crash experience, speed, alignment, and roadside features. Using bivariate and multivariate statistical analyses, the study investigated the crash experience along the corridor as well as some of the underlying relationships which could explain some of the crash causal factors. Results show a strong association between crash rates and horizontal curvatures even for flat curves that can be negotiated at speeds above the posted speed limit, per the highway design equations. Higher crash rates were also found to be associated with the difference between the observed free-flow speeds and the speed dictated by the curve radius or sight distance as per the design equations. Further, results strongly support the safety benefits of guardrails as evidenced by the lower crash rates and severities. The presence of fixed objects and the steepness of side slopes were also found to have an effect on crash rates and severities.
Where are the electric vehicles? A spatial model for vehicle-choice count data
(2015-02) Chen, T. Donna; Wang, Yiyi; Kockelman, Kara M.
Electric vehicles (EVs) are predicted to increase in market share as auto manufacturers introduce more fuel efficient vehicles to meet stricter fuel economy mandates and fossil fuel costs remain unpredictable. Reflecting spatial autocorrelation while controlling for a variety of demographic and locational (e.g., built environment) attributes, the zone-level spatial count model in this paper offers valuable information for power providers and charging station location decisions. By anticipating over 745,000 personal-vehicle registrations across a sample of 1000 census block groups in the Philadelphia region, a trivariate Poisson-lognormal conditional autoregressive (CAR) model anticipates Prius hybrid EV, other EV, and conventional vehicle ownership levels. Initial results signal higher EV ownership rates in more central zones with higher household incomes, along with significant residual spatial autocorrelation, suggesting that spatially-correlated latent variables and/or peer (neighbor) effects on purchase decisions are present. Such data sets will become more comprehensive and informative as EV market shares rise. This work’s multivariate Poisson-lognormal CAR modeling approach offers a rigorous, behaviorally-defensible framework for spatial patterns in choice behavior.
Use of Finite Difference Numerical Technique to Evaluate Deep Patch Embankment Repair with Geosynthetics
(2015-03) Perkins, Steve W.; Cuelho, Eli V.; Akin, Michelle; Collins, Brian
Low-volume roads constructed in steep hillside terrain by cut and cast techniques may experience instability in the form of excessive subsidence that leads to large cracks and differential movement along the roadway bench. The technique of deep patch embankment repair with geosynthetics (DPERG) has been employed in the western United States; DPERG generally involves a 1- to 2-m-deep excavation that is backfilled with compacted granular soils and one or more layers of geosynthetic reinforcement. The design goal of a DPERG is not necessarily to eliminate future slope movement but to confine potential failure surfaces to a region of the slope well below the roadway bench and extending out to the slope face such that a failure surface does not extend up onto the roadway bench. This design results in movement along the roadway bench that is more uniform and less disruptive to traffic. This paper describes the results of a study to evaluate the DPERG technique by analytical methods supported by field observations for the purpose of determining the required depth of the DPERG and the optimum layer spacing of the reinforcement. The study showed that for a given slope geometry and set of soil properties that had led to failure in an unreinforced slope, there were several combinations of DPERG depth and number of reinforcement layers that satisfied the design goal. The study showed that more tightly spaced reinforcement layers were beneficial and that for widely spaced layers, the design goal of a DPERG could not be met, even for a thick DPERG depth.
Effect of cold temperatures on the shear behavior of glued laminated beams
(2015-04) Drake, Garrett; Berry, Michael; Schroeder, David
This study evaluated the effects of subfreezing temperatures and moisture content on the shear behavior of glulam beams. Full-scale glulam beams (79 mm by 229 mm deep) at two moisture contents (12 and 28%) and three temperatures (20 Â°C, 0 Â°C, and âˆ’ 40 Â°C) were tested in four-point bending until failure. Temperature was observed to affect the failure mechanism of the beams, with the beams tested at 0 Â°C and 20 Â°C failing in shear and the beams tested at âˆ’ 40 Â°C failing in tension. Further, the strengths of the beams and their stiffnesses were observed to increase with decreasing temperature, with these effects being more pronounced in the higher moisture content beams. Over the temperature range of 20 Â°C to âˆ’ 40 Â°C, the 12 percent moisture content beams observed strength and stiffness gains of 17 and 22%, while the 28 percent moisture content beams observed respective gains of 37% and 66%.
Whole cell kinetics of ureolysis by Sporosarcina pasteurii
(2015-06) Lauchnor, Ellen G.; Topp, D. M.; Cunningham, Alfred B.; Gerlach, Robin
Aims Ureolysis drives microbially induced calcium carbonate precipitation (MICP). MICP models typically employ simplified urea hydrolysis kinetics that do not account for cell density, pH effect or product inhibition. Here, ureolysis rate studies with whole cells of Sporosarcina pasteurii aimed to determine the relationship between ureolysis rate and concentrations of (i) urea, (ii) cells, (iii) and (iv) pH (H+ activity). Methods and Results Batch ureolysis rate experiments were performed with suspended cells of S. pasteurii and one parameter was varied in each set of experiments. A Michaelis–Menten model for urea dependence was fitted to the rate data (R2 = 0·95) using a nonlinear mixed effects statistical model. The resulting half-saturation coefficient, Km, was 305 mmol l−1 and maximum rate constant, Vmax, was 200 mmol l−1 h−1. However, a first-order model with k1 = 0·35 h−1 fit the data better (R2 = 0·99) for urea concentrations up to 330 mmol l−1. Cell concentrations in the range tested (1 × 107–2 × 108 CFU ml−1) were linearly correlated with ureolysis rate (cell dependent = 6·4 × 10−9 mmol CFU−1 h−1). Conclusions Neither pH (6–9) nor ammonium concentrations up to 0·19 mol l−1 had significant effects on the ureolysis rate and are not necessary in kinetic modelling of ureolysis. Thus, we conclude that first-order kinetics with respect to urea and cell concentrations are likely sufficient to describe urea hydrolysis rates at most relevant concentrations. Significance and Impact of the Study These results can be used in simulations of ureolysis driven processes such as microbially induced mineral precipitation and they verify that under the stated conditions, a simplified first-order rate for ureolysis can be employed. The study shows that the kinetic models developed for enzyme kinetics of urease do not apply to whole cells of S. pasteurii.
Sedimentological Analyses of Eggshell Transport & Deposition: Implication and Application to Eggshell Taphonomy
(2015-06) Imai, Takuya; Varricchio, David J.; Cahoon, Joel; Plymesser, Kathryn
The interpretation of fossil eggshells can be problematic because eggshells may be transported by hydraulic flow in floodplains, making it difficult to interpret the reproductive behavior and ecology of parent animals. A series of flume studies was conducted to establish analytical techniques for assessing eggshell hydraulic transport in the fossil record. We investigated preferred eggshell orientation after transport, the relationship of flow competence with eggshell height and volume, and the size of clastic sediment expected to be associated with transported eggshells. Goose, emu, and ostrich eggshell fragments were released in a flume with decelerating flow. The transport of each eggshell was observed five times on each of four substrates (coarse sand, sparse gravel, dense gravel, and polyvinyl chloride). At eggshell deposition, eggshell orientation and flow depths were recorded. Critical bed shear stress for eggshell deposition was estimated based on the flow depth at the point of eggshell deposition, tested relative to eggshell height and volume, and used to estimate the size of hydraulically equivalent particles. The probability of concave-down orientation after transport was > 85% regardless of eggshell type or substrate. The bed shear stress at eggshell deposition reflected the eggshell height and volume. The estimated size of hydraulically equivalent particles was coarse sand or larger. A high proportion of concave-down eggshells in a fossil assemblage may indicate transport. In addition, eggshells may be sorted according to their height and volume. Coarse sand or larger particles observed in a matrix of fossil eggshells may suggest eggshell transport.
Estimation of Seasonal Daily Traffic Flow of Agricultural Products and Implications for Implementation of Automatic Traffic Recorders
(2015-06) Forsythe, Shane; Stephens, Jerry; Wang, Yiyi
Reliable traffic counts on a highway system are critical for sound decision making about the maintenance, operation, and expansion of the system. Portable short-term automatic traffic recorders (ATRs) are a cost-efficient way to complement traffic counts from permanent ATR sites by performing temporary traffic counts on the highway system. Complicating the collection of traffic data with these short-term devices is the seasonal variation in vehicle operations throughout the year. This work focused on predicting the spatial distribution of seasonal traffic resulting from agricultural activities by using a new method that combines geographic information system spatial functions and the four-step travel demand model. This research collected information about township grids for Montana (as proxies for trip origins), grain elevators (trip destinations), agricultural ground cover, and crop yield estimates to estimate flows in tonnage at the grid level on the road network. Results suggest that the proposed method using the location of major crops and the locations of grain elevators can be used to predict tonnage of product that will be added to individual routes. The predicted values can then be compared with reported heavy-truck traffic to locate sites that may have underrepresented traffic flows. Although this work considered specifically three crops, the method can be applied to any resource flow that has known origin and destination information. The method can be enhanced by refining assumptions of the composition of heavy trucks transporting agricultural products and by field measurements of vehicle flows to better test the validity of the model.
Bulk electric conductivity response to soil and rock CO2 concentration during controlled CO2 release experiments: Observations & analytic modeling
(2015-09) Jewell, Scott; Zhou, Xiaobing; Apple, Martha E.; Dobeck, Laura M.; Spangler, Lee H.; Cunningham, Alfred B.
To develop monitoring technologies for geologic CO2 storage, controlled CO2 release experiments at the Zero Emissions Research and Technology (ZERT) site in Bozeman, Montana, USA, were carried out in 2009-2011. To understand the impact on the electric properties of soil and sediment rock due to possible CO2 leakage, we have developed an analytical model to explain and predict the electric conductivity (EC) for CO2 impacted soil and sedimentary rock. Results from the model were compared with the measurements at the ZERT site during 2009â€“2011 and the CO2-Vadose Project site in France in 2011-2012 after model calibration at each site. The model was calibrated using the saturation (n) and cementation (m) exponents contained in Archie's equation, and a chemistry coefficient (pKc) as tuning parameters that minimized the misfit between observed and modeled soil/rock bulk conductivity data. The calibration resulted in n=3.15, m=2.95, and pKc=4.7 for the ZERT site, which was within the range of values in the literature. All the ZERT data sets had rms errors of 0.0115-0.0724. For the CO2-Vadose site, calibration resulted in n=3.6-9.85 and m=2.5-4.2, pKc=4.80-5.65, and the rms error of 0.0002-0.0003; the cementation exponents were consistent with the literature. These results found that the model predicted the bulk EC reasonably well in soil and rock once the unmeasurable model parameters (n, m, and pKc) were calibrated.
Perceived Risk of Phoning While Driving: A Case Study from Jordan
(2015-10) Ismeik, Muhannad; Al-Kaisy, Ahmed; Al-Ansari, Khalid
The use of mobile phones while driving is banned in most countries since it impairs driving performance and is believed to increase crash risk. The aim of this research is to identify the prevalence of phoning while driving in Jordan and to examine the association between drivers’ perception of risk and potential predicting variables. A sample of 423 drivers was surveyed to gather information on their mobile phone use while driving as well as their risk perception. Data collection took place anonymously at diverse locations through a self-report questionnaire. Statistical analysis was performed to highlight the association between risk levels and drivers’ demographics and exposure characteristics. An alarming rate of 93.1% of drivers, mostly young male college students, engaged in this unsafe behavior despite being aware of the associated risk and legislative laws. Findings suggested gender, employment status, age, education level, driving experience, and daily traveled distance were associated with mobile phone use while driving. Recommendations to enhance traffic safety were proposed and further research directions were highlighted.
Traffic Safety Along Tourist Routes in Rural Areas
(2016-01) Wang, Yiyi; Veneziano, David; Russell, Sam; Al-Kaisy, Ahmed
Little is known about the safety of tourist drivers in the United States. Most domestic studies have focused on traffic deaths and injuries of U.S. citizens traveling abroad and cite factors such as driving on the left, lack of seat belt use, and alcohol consumption. U.S. states that have a number of tourist attractions and the roadways to reach them may be interested in whether traffic safety is problematic for drivers who are tourists. To that end, this research investigated the contributing factors for crash severity and crash likelihood of visiting drivers in or near three national parks in rural areas. Driver-level data from the Rocky Mountain National Park in Colorado and the Sequoia and Kings Canyon National Parks in California revealed risk factors for crash severity, including age, geometry, and seat belt use. The second data set offered a more microscopic view at the road level and was used to anticipate crash frequency of visiting drivers at the road link level. Moreover, the second data set contained road geometry, traffic volume, environment, and crash counts aggregated at the segment level along a 57.8-mi stretch of U.S. Hwy 89 (a primary route to the north gate of Yellowstone National Park) in Montana that is frequently used by tourists. Crash risk factors (e.g., geometry and traffic intensity) affected local and nonlocal (tourist) drivers in different ways. Further exploration of crash trends in specific parks would be valuable in understanding the overall trends and contributors to crashes in tourism areas and to determine effective improvement measures.