Iowa Department Of Transportation Research Articles

Evaluation of the Earth Pressure Acting on Concrete Box Culverts

Earth pressure on concrete box culverts is a key component of design and load-rating decisions. The American Association of State Highway and Transportation Officials has revised the design guidelines over the years to impose greater design/rating earth pressures for buried structures. Currently, the Iowa Department of Transportation uses the maximum and minimum lateral earth pressure of 36/18 lb/ft3 specified for load factor design (LFD) and allowable stress design (ASD) and 60/30 lb/ft3 for load and resistance factor design (LRFD). The objective of this research is to monitor and evaluate the real earth pressures acting on deep-buried culvert structures. To achieve this objective, two concrete box culverts–one in Ida County and the other in Crawford County–were monitored for more than 2.5 years and 1 year, respectively, to identify the realistic design soil pressure. The captured pressure, strain, and temperature data were analyzed to find the relation between the temperature and earth pressure experienced by the culverts. The measured vertical and lateral pressures were compared with the specified design pressure loading. The monitoring results from both culverts led to the consistent conclusion that the earth pressure experienced by the culverts was two to six times that of the design values with the LRFD and LFD/ASD methods. This paper revealed that the earth pressure acting on the deeply embedded culvert could be higher than the design-specified value. Further research was recommended to investigate the relation between the soil weight and culvert vertical/lateral pressure for Iowa design specifications.

Rates and predictors of teen driver crash culpability

Background: Motor-vehicle crash risk is highest among teen drivers. Despite a wealth of research on the topic, there are still many contributors to these crashes that are not well understood. The current study sought to examine the contribution of graduated driver licensing (GDL) restrictions, sex, age, roadway circumstances, and citation history to teen drivers’ crash culpability. Method: Crash system data from the Iowa Department of Transportation were linked with traffic-related charges from the Iowa Court Information System. Crashes involving teens aged 14 to 17 years between 2016 and 2019 were analyzed (N = 19,847). Culpability was determined using the driver contributing circumstances from the crash report. Moving and non-moving traffic citations issued prior to the date of each crash were considered. A multivariable logistic regression model was constructed to examine predictors of crash culpability. Results: Teen drivers were determined to be culpable for more than two thirds of crashes (N = 13,604, 68.54%). Culpability was more prevalent among males, younger teens, in rural areas, in the presence of reported roadway contributing circumstances, during hours of restricted nighttime driving, and among teens with citation histories that included both moving and non-moving citations. Similarly, multivariable model results indicated that the likelihood of culpability was higher among males, in rural areas, and at each stage of GDL compared to teen drivers with unrestricted licenses. While drivers with a history of both moving and non-moving violations were more likely to be culpable, those with a history of only moving or only non-moving violations were less likely to be culpable compared to those with no violation history. Conclusion: Sex, crash location, and GDL stage were associated with teen driver crash culpability. A singular prior moving or non-moving violation may play a protective role in teen crash culpability.

PERFORMANCE OF POLYMER GROUTS MADE FROM WASTES FOR PERMEABLE RIGID PAVEMENT CONNECTIONS

This research developed polymer grouts made from wastes such as fly ash, palm oil fuel ash, and silica fume. The selected polymer grouts served as an interlocking key between the StormPav covers and as a grout to seal the gaps between the interlocking keys and StormPav covers. Based on compressive strength and workability of the polymer grouts, mix ratio of resin to fly ash = 1:1.00 was chosen as the grout, while mix ratio of resin to fly ash = 1:1.50 was used to form an interlocking key. Mix ratios of resin to fly ash = 1:1.00 and resin to fly ash = 1:1.50 had a compressive strength of 98.90 MPa and 81.70 MPa, respectively, and flexural strength of 53.00 MPa and 61.90 MPa. Moreover, increasing the fly ash content in polymer grout decreased the water absorption and volume of permeable voids. In terms of shear strength, the mix ratio of resin to fly ash = 1:1.00 performed well as grout, with a determined shear strength of 3.98 MPa. Even after 25 days of exposure to the high concentration of sodium hydroxide, sulphuric acid, sodium chloride, and magnesium sulphate, the determined shear strength met the minimum shear strength requirement of 1.38 MPa as stated by the Iowa Department of Transportation. Therefore, it can be concluded that both selected mix ratios were suitable for use as grout and interlocking key due to their good physical and mechanical properties.

Spatial Analysis of Relationships Between Intersection Safety, the Urban Built Environment, and Average Income Level: A Case Study of Des Moines

This study makes a methodological contribution by exploring the relationship between motor vehicle traffic crashes at intersections and the built environment. The study focuses on specific neighborhoods within the city of Des Moines, Iowa, with contrasting socio-economic characteristics to examine variation between the neighborhoods. Exploratory spatial data analysis was used to locate crash clusters at intersections using seven-year crash data (2013–2019) obtained from the Iowa Department of Transportation. Google Street View was used to survey the built environment variables. Regression modeling was then utilized to establish a relationship between intersection crash clusters and the built environment. The results show that commercial/institutional land uses, bus stops, and signalized intersections are statistically significant and have a positive impact on intersection crash incidence. Additionally, crash incidences were higher in neighborhoods with below-average income percentages. These findings potentially can enlighten policymakers to focus on appropriate safety treatments such as traffic-calming measures and identify areas where traffic safety policies need to be prioritized. Policy re-evaluation for bus stop locations and design ideas for the urban form could be established to reduce motor vehicle intersection crashes.

Cross-asset prioritization model for transportation projects using multi-attribute utility theory: a case study

The Moving Ahead for Progress in the 21st Century Act (MAP-21), enacted by the US Congress in 2012, establishes seven national infrastructure performance goals that must be considered during funding allocation procedures by state transportation agencies (STAs). These goals’ wide range of aspects creates situations where STAs have to deal with conflicting objectives without formal trade-off mechanisms, forcing them to make investments that might be difficult to justify to stakeholders. Moreover, STAs strive to create standard performance metrics that allow the comparison of investment alternatives among different groups of assets. This paper presents a case study on applying a Multi-Attribute Utility Theory (MAUT) model to make trade-offs among conflicting objectives in different types of transportation construction projects. The case study was conducted on ten construction projects executed by the Iowa Department of Transportation. The case study shows how the proposed MAUT model can be used as an objective mechanism to prioritize infrastructure projects across asset classes to provide the necessary justification for infrastructure policy decision-making.

Inherent variability assessment from sparse property data of overburden soils and intermediate geomaterials using random field approaches

ABSTRACT This study assesses the inherent variability in the geomaterial parameter by quantifying the parameter uncertainty and develops a site investigation plan with a low degree of uncertainty. A key research motivation was using sparse borehole data to predict a site geomaterial configuration in order to determine the design of a site investigation plan. This study develops a systematic methodology for carrying out a study of inherent variability in light of the limitations posed by borehole data. The data in this study was provided by the Iowa Department of Transportation which consisted of eight boreholes from which 92 associated SPT N-values was considered as the geomaterial parameter of interest. The systematic methodology then involved the following steps. A general linear model was employed to fit and compare various spatial covariance models with and without a nugget. These spatial covariance models were also evaluated with variograms. Predicted SPT N-values were generated using universal kriging. Simulations were performed conditionally and unconditionally to identify optimal site investigation plans. The results identified site investigation plans with reduced parameter uncertainty. The proposed approach can produce site investigation plans that target any or all geomaterial layers to reduce uncertainty with respect to any geomaterial parameter of interest.

The dark side of nighttime all-terrain vehicle use

BackgroundDriving at night is considered a risk factor for all-terrain vehicle (ATV) crashes and injuries but few studies have addressed this issue. Our objective was to compare daytime and nighttime ATV crashes to better understand the potential risk factors associated with riding at night.MethodsA retrospective study was conducted on Iowa ATV-related crashes and injuries from January 1, 2002 through December 31, 2019 using four statewide datasets: the Iowa Department of Transportation (2002–2019), the Iowa Department of Natural Resources (2002–2019), the Iowa State Trauma Registry (2002–2018) and Iowa newspaper clippings (2009–2019). A standardized coding system was developed, and matching records were identified using Link Plus®. Descriptive (frequencies) and bivariate (chi-square, Fisher's exact test) analyses were performed using VassarStats (Statistical Computation Website).ResultsAmong crash victims where light conditions were documented (2125/3752, 57%), about one-quarter (485/2125, 23%) were injured at night. Nighttime crash victims were less likely youth (14% vs. 30%, p < 0.0001), less likely to be wearing helmets (11% vs. 18%, p = 0.003), and less frequently involved in motor vehicle crashes (7% vs. 14%, p < 0.0001) as compared to daytime victims. Nighttime victims were also more likely to be passengers (22% vs. 15%, p = 0.002), to test positive for alcohol (44% vs. 13% in adults, p < 0.0001), and to be injured on a roadway (53% vs. 45%, p = 0.007) and on weekends (76% vs. 63%, p < 0.0001). Numerous differences between daytime and nighttime characteristics were observed for males, females, and adults, whereas most characteristics were similar for youth. The severity of injuries and proportion of fatalities were similar among daytime and nighttime crash victims.ConclusionsNighttime crash victims, particularly adults, were characterized by more frequent risky behaviors like carrying passengers, roadway riding, alcohol use, and lack of helmets. Whereas the frequency of risky behaviors among youth was similar for daytime and nighttime crashes, these behaviors put children at potential risk for injury. Multi-factorial, targeted injury prevention strategies are needed, including improved vehicle design, education about the dangers of nighttime operation, and passage and enforcement of ATV safety laws. Particularly relevant to our study are laws that prohibit nighttime riding.

A Risk Management Database Framework Implementation for Transportation Asset Management

A 2017 survey of the state of practice on how agencies are developing their risk-based asset management plan shows that state highway agencies are increasingly adapting the way they do business to include explicit considerations of risks. At the moment, this consideration of risk is not linked to data. Hence, there is a lack of integration of risk management in driving strategic cross-asset programming and decision-making. This paper proposes and implements a risk management database framework as the missing piece in the full implementation of a risk-based transportation asset management program. This risk management database framework utilizes Geographic Information Systems (GIS) and Application Programming Interface (API) to implement a risk management database of all the relevant variables an agency needs for risk modeling to improve risk monitoring, risk register updates, and decision-making. This approach allows the use of existing enterprise as well as legacy data collection systems, which eliminates the need for any capital-intensive implementation cost. Furthermore, it provides transportation agencies with the ability to track risk in quantitative terms, a framework for prioritizing risk, and the development of an actionable plan for risk mitigation. In this paper, the implementation of the fully integrated GIS-enabled risk management database employs the Iowa department of transportation (DOT) data and risk register.

Analytical methods to determine effectiveness of slurry seals in wet/freeze climate using pavement management information systems

With increasing economic pressures worldwide, the amount of money spent on pavement preservation needs to become more effectively utilised. Historically, the Long-Term Pavement Performance (LTPP) study has led to data-driven performance expectations for treatments. Pavement management systems (PMS) allowed many to form analytical methods to evaluate pavement performance, from trend fitting to benefit analysis. Taking these methods and applying them to the Iowa Department of Transportation’s (DOT) pavement management information system (PMIS) database can determine preservation utility as well as provide expectations of pavement treatments. Thirteen slurry seal projects across the wet/freeze climate of Iowa, U.S.A., were analysed to determine the service life extensions and yearly benefit for their pavement condition, rutting, riding, and cracking indices. This study aims to provide a framework for future analysis of more preservation treatments and other PMS databases. Understanding local performance of various preservation methods leads to better pavement management and economically sound decisions.

Use of Deep Learning to Study Modeling Deterioration of Pavements a Case Study in Iowa

This paper describes the process and outcome of deterioration modeling for three different pavement types (asphalt, concrete, and composite) in the state of Iowa. Pavement condition data is collected by the Iowa Department of Transportation (DOT) and stored in a Pavement-Management Information System (PMIS). In the state of Iowa, the overall pavement condition is quantified using the Pavement Condition Index (PCI), which is a weighted average of indices representing different types of distress, roughness, and deflection. Deterioration models of PCI as a function of time were developed for the different pavement types using two modeling approaches. The first approach is the long/short-term memory (LSTM), a subset of a recurrent neural network. The second approach, used by the Iowa DOT, is developing individual regression models for each section of the different pavement types. A comparison is made between the two approaches to assess the accuracy of each model. The results show that the LSTM model achieved a higher prediction accuracy over time for all different pavement types.

293 The Dangers of Off-Road Vehicles to Youths: Not Something to Kid Around About

Children are not allowed to operate motor vehicles such as cars until they are 16 years old due to the risks associated with the operation of such powerful machines. Yet, the operation of off-road vehicles (ORVs) by youths under 16 years old has been largely normalized in both rural and urban communities, despite the significant safety risks involved. To better understand this issue, the goal of this study was to characterize roadway ORV crashes with youth operators, including riding behaviors and crash outcomes, in a Midwest state. This study examined ORV roadway crashes involving operators <16 years of age (115 crashes) that were documented in Iowa Department of Transportation (DOT) records from 2002-2017. Descriptive and comparative analyses was performed using the Statistical Package for the Social Sciences (SPSS). In Iowa’s pediatric roadway crashes from 2002-2017, 63% of victims were male and 81% were 12-15 years old. Females were more commonly passengers than were males (60% vs. 24%), as were younger (<12 years) as compared to older riders (56% vs. 26%). Only a small percentage of victims were helmeted, 24% of operators and 14% of passengers. Additionally, 73% of all roadway crashes involved multiple riders on the ATV, around 40% occurred on paved roads, and 82% occurred in rural areas. Collisions with an object or another vehicle were the mechanism in 65% of crashes. Roads with speed limits over 50 mph were the location of around half (52%) of all crashes. Among pediatric victims, 3.5% were killed in the crash and 46% of the pediatric roadway crashes resulted in either major injury or death. Moreover, a higher proportion of the fatal or incapacitating injuries were observed in adolescents (12-15 years) than in younger children (35% vs. 23%). Our results illustrate that multiple risky behaviors are common among youth in roadway ORV crashes, including riding on high speed roads, with passengers, and/or without helmets. Adolescents (12-15 years old) are the large majority of pediatric victims, and serious injury or death resulted in almost half of all crashes. Based on these results, it is clear that multiple targeted approaches are needed for youth under 16 years old in order to prevent pediatric fatalities and severe injuries, particularly on the road.

Evaluation of Regionally Calibrated Load and Resistance Factor-Design Method Used for Driven-Steel H-Piles

Since October 2007, the Federal Highway Administration (FHWA) has required the implementation of LRFD methods in all new bridge designs, including pile design. The resistance factors provided nationally for LRFD of driven piles are relatively conservative. Therefore, the Iowa Department of Transportation and Iowa State University collaborated and established regional resistance factors that are more efficient than those provided in the AASHTO Specifications, which are complemented with improved construction control methods. Iowa's LRFD guidelines for piles have been used in enough completed projects since 2012, allowing an assessment of the accuracy of the regional resistance factors and construction control methods. The piles used in these projects included both end-bearing piles in rock and friction piles. The friction piles were installed in cohesive, noncohesive, and mixed soil sites. The evaluation for the different pile categories and soil types found that the regional LRFD resistance factors developed were successfully applied in Iowa's driven pile design and effectively reduced the piles' contract lengths, resulting in cost–benefit over AASHTO's recommended resistance factors.

Incorporating Pavement Smoothness Benefits to Enhance the Iowa Department of Transportation’s Pavement Type Determination Process

The Federal Highway Administration (FHWA)’s Pavement Policy as codified in 23 CFR 626 states, “Pavement shall be designed to accommodate current and predicted traffic needs in a safe, durable, and cost effective manner” to be eligible for federal highway funding. To meet this requirement, state highway agencies have developed pavement type determination (PTD) policies, also known as pavement type selection, and implemented pavement management. Iowa Department of Transportation (DOT)’s PTD has been in place for many years; but in 2018, Iowa DOT looked at enhancing their PTD process to address gaps between past practice and best practice. Among the enhancements, user benefit as defined by pavement smoothness was utilized when net present value (NPV) alone could not definitively distinguish a preferred alternative. The smoothness benefit would become the divisor in a cost–benefit (C/B) ratio that would be used to determine the preferred alternate for the PTD. The cost portion of the ratio would remain the NPV of agency costs for the construction and projected rehabilitations during the analysis period. After a literature review and interviews of comparable state DOTs, several modifications to Iowa DOT’s PTD and the C/B ratio were analyzed and adopted. The modifications range from accepted practice changes, such as the use of a longer analysis period (50 years), to unconventional techniques, such as the consideration of smoothness. Iowa DOT believes these changes provide a more robust PTD. They are also considering additional improvements based upon additional research and policy making.

Characteristics of crashes and injuries among 14 and 15 year old drivers, by rurality

Purpose: Motor-vehicle crashes continue to be the leading cause of death for teenagers in the United States. The United States has some of the youngest legal driving ages worldwide. The objective of this study was to determine rates and factors associated with injury crashes among 14- and 15-year-old drivers and how these varied by rurality. Methods: Data for this cross-sectional study of 14- and 15-year-old drivers were obtained from the Iowa Department of Transportation from 2001 to 2013. Crash and injury crash rates were calculated by rurality. The relationship between crash and driver factors and injury was assessed using logistic regression. Findings: Teen drivers, aged 14 and 15 years, had a statewide crash rate of 8 per 1,000 drivers from 2001 to 2013. The majority of crashes occurred in urban areas (51%), followed by in town (29%), remote rural areas (13%), and suburban areas (7%). Crash and injury crash rates increased as level of rurality increased. The odds of an injury crash increased more than 10-fold with the presence of multiple other teens as passengers, compared to no passengers (OR = 10.7, 95% CI: 7.1–16.2). Conclusions: Although 14- and 15-year-old drivers in Iowa have either limited unsupervised (school permits) or supervised only driving restrictions, they are overrepresented in terms of crashes and injury crashes. Rural roads and multiple teen passengers are particularly problematic in terms of injury outcomes. Practical applications: Results from this study support passenger restrictions and teen driving interventions designed with a rural focus.

Screening for Driver Disorientation at the Iowa Department of Transportation, Motor Vehicle Division

Background and Purpose: Aging is associated with cognitive impairment, which interferes with safe driving ability. Cognitively-impaired drivers may present as confused and belligerent, creating challenges in differentiating these drivers from intoxicated or metabolically-impaired drivers. The Driver Orientation Screen for Cognitive Impairment (DOSCI) was developed to assist identification of disorientation and was piloted in the Iowa Department of Transportation. This study examined the feasibility, acceptability, and usefulness of the DOSCI at licensing agency offices, and to investigate the association between DOSCI performance and driver licensing outcomes. Methods: A sample of 2,510 DOSCI screens from 2,399 individuals was assessed. Data included the acceptability of the DOSCI among staff and clients, time to complete assessments, DOSCI outcomes, and final driver license status. Results: On a 5-point scale, mean score was 4.76 (SD=0.67) for Ease of Administration, 4.67 (SD=0.80) for Acceptance by Client, and 3.81 (SD=1.57) for Useful in Assessment. Clients who failed the assessment had significantly higher odds of not receiving a driver’s license than clients who passed (OR=2.556). Conclusion: The DOSCI was quick to administer, well-accepted, and was associated with licensing outcome. The tool has potential to contribute to traffic injury prevention by identifying potentially impaired drivers requiring closer examination in a licensing agency setting.

Developing an Optimized UI for Traffic Incident Managers

Traffic Incident Managers (TIMs) coordinate first responders and help resolve traffic-related incidents. Currently, some use over fifteen different software applications with unique functionalities across three monitors to manage incidents, leading to redundant data entry, unnecessary task switching, and delayed responses. 40 hours of TIMs’ screens were recorded during their normal work hours at the Iowa Department of Transportation (DoT). The resulting task analysis from these videos greatly influenced the design of a simplified, web-based, user interface (UI) prototype. The new UI offers a 42.9% reduction in the steps required to manage an incident by combining the functionality of the fifteen different applications used in the existing system into a single, structured UI. This research approach offers a UI model to other DoTs that can lead to faster and more effective incident management.

Does crash risk increase when emergency vehicles are driving with lights and sirens?

IntroductionEmergency vehicles, such as police, ambulances, and fire vehicles, need to arrive at the scene of emergencies as quickly as possible, and thus they often travel in emergency mode – using their lights and sirens and often bypassing traffic signals. We examined whether travelling in emergency mode increased crash risk among police, ambulance and fire vehicles. MethodsWe conducted a quasi-induced exposure analysis using data from the Iowa Crash Database for the period of 2005 through 2013. The data are maintained by the Iowa Department of Transportation (IADOT), Office of Driver Services (ODS) and includes all investigating police officer's reports of motor vehicle crashes. The quasi-induced exposure method is an approach to calculate crash risk in the absence of exposure data using vehicles without a contributing cause (did not contribute to the crash) as a proxy for the baseline driving population. ResultsFrom 2005 – 2013, police vehicles were involved in 2406 crashes and ambulances and fire vehicles were involved in 528 crashes. Police vehicles were 1.8 times more likely to crash while driving in emergency mode than usual mode; this was a statistically significant increase. Ambulance and fire vehicles were not more likely to crash in emergency mode compared with usual mode. For police, other factors that contributed to crash risk included gender, age, icy/snowy roads, unpaved roads, and intersections. For ambulances and fire vehicles, other factors that contributed to crash risk included gender, age, weekends, icy/snowy roads and urban locations. ConclusionCrash risk increased when police vehicles drove with lights and sirens but did not increase for ambulance and fire vehicles. Further research is necessary to develop and evaluate strategies to mitigate crash risk among police vehicles. Cultural approaches which prioritize transportation safety in conjunction with reaching the scene as quickly as possible may be warranted.

Affirmative Action Exemptions and Capacity Constrained Firms

This paper studies how affirmative action exemptions in public procurement can improve efficiency and government expenditures without harming disadvantaged business enterprise (DBE) utilization. I examine a unique program employed by the Iowa Department of Transportation, where prior to 2013 prime contractors were allowed an exemption from a project's affirmative action requirement if their history of DBE utilization was sufficiently high. I find that prime contractors use the exemption to smooth demands on capacity constrained DBEs, building a history of utilization during low demand periods and exploiting the resulting exemption during high demand. The exemption policy was unexpectedly eliminated in 2013, which I exploit to evaluate its effect on DBE utilization and procurement costs. I find that average DBE utilization was unchanged and bids rose on affirmative action contracts. (JEL D22, H76, J15, J16)

The effects of roadway characteristics on farm equipment crashes: a geographic information systems approach.

BackgroundTractors and other slow-moving self-propelled farm equipment are often used on public roadway to transfer goods from the farm to a market or distributer. Increased roadway exposure has led to a growing concern on the occurrence of farm equipment crashes. This study aims to compare characteristics of road segments with farm equipment crashes to road segments without farm equipment crashes in the state of Iowa.MethodsData were obtained from the Iowa Department of Transportation from 2005 to 2011 on all crashes involving farm equipment, and features of all Iowa roadways. Geographic Information Systems (GIS) was used to identify geospatial features, such as road type, speed limit, traffic volume surface type, road and shoulder width of where a crash occurred. Logistic regression models were used to measure the associations between road characteristics and the occurrence of farm equipment crashes. Crude and adjusted odds ratios and 95% confidence intervals were reported.ResultsA total of 1371 farm equipment crashes were reported in Iowa over the 6-year period and geocoded onto a street location. As traffic volume increased, the odds of a crash occurring also increased. Roadways with posted speed limits between 50 and 60 mph were associated with a higher odds of having crashes on them compared to roadways with speeds less than 35 mph (OR = 8.05, 95% CI: 6.59–9.84). Iowa routes (OR = 5.98, 95% CI: 4.97–7.20) had the highest odds of having crashes compared to local routes. Increased road width (OR = 0.90, 95% CI: 0.86–0.94) was associated with a 10% decrease in the odds of a crash.ConclusionsHigher traffic volume, higher posted speed limits, road type, and smaller road widths were associated with the occurrence of farm equipment crashes. Findings from this study can be used to guide policy to improve roadway design and conditions for all road users.Electronic supplementary materialThe online version of this article (doi:10.1186/s40621-016-0096-1) contains supplementary material, which is available to authorized users.

Pavement Marking Retroreflectivity and Crash Frequency: Segmentation, Line Type, and Imputation Effects

This paper investigates the effects of segment length, line types, and imputed retroreflectivity values on pavement-marking retroreflectivity and crash frequency analyses. Road data, crash data, pavement condition data, and pavement-marking retroreflectivity data from Iowa Department of Transportation (DOT) databases were acquired and spatially integrated. Data sets for 1-, 3-, and 5-mi segments were prepared to investigate the effect of segmentation. Additional data sets with imputed and measured retroreflectivity data were prepared for comparison. A series of negative binomial regression analyses were run to estimate the expected number of crashes on varying segment lengths and data subsets based on the two retroreflectivity collection methods. The findings show that using smaller segments and data sets with measured retroreflectivity rather than imputed retroreflectivity leads to a more significant relationship between the retroreflectivity of longitudinal pavement markings and crash frequency. The findings also suggest that keeping longitudinal pavement markings in good condition has significant positive effects on safety. The results further suggested that the expected number of annual crashes significantly decreased with the increasing retroreflectivity of white-edge lines (WELs) and yellow-edge lines (YELs) for four-lane road segments. In addition, a significant relationship between pavement condition, measured with the International Roughness Index (IRI) and the expected number of crashes was found for all data sets.