Thomas H Maze

Whether Weather Matters to Traffic Demand, Traffic Safety, and Traffic Operations and Flow

Weather affects many aspects of transportation, but three dimensions of weather impact on highway traffic are predominant and measureable. Inclement weather affects traffic demand, traffic safety, and traffic flow relationships. Understanding these relationships will help highway agencies select better management strategies and create more efficient operating policies. For example, it was found that severe winter storms bring a higher risk of being involved in a crash by as much as 25 times—much higher than the increased risk brought by behaviors that state governments already have placed sanctions against, such as speeding or drunk driving. Given the heightened risk of drivers involvement in a crash, highway agencies might wish to manage better and restrict use of highways during times of extreme weather, to reduce safety costs and costs associated with rescuing stranded and injured motorists in the worst weather conditions. However, the first step in managing the transportation systems to minimize the ...

Rural Expressway Intersection Characteristics as Factors in Reducing Safety Performance

Expressways have been constructed in many states as a way to increase mobility without the expense of a full access-controlled grade-separated facility. In most cases, it was assumed that these segments of highway would produce similar mobility and safety characteristics as other access-controlled facilities. However, recent research has found that there are problems with the safety performance of these systems. The objective of these analyses is to identify the major contributing factors that create problematic intersections in Iowa. From previous research, it is evident that factors in addition to roadway volume contribute to the safety performance of an at-grade, two-way, stop-controlled expressway intersection. This research identifies additional characteristics that may increase or decrease the safety performance of a rural expressway intersection. The methodology used in this research includes the examination of 644 intersections throughout Iowa. Through the use of a statewide database and crash information from 1996 to 2000, it was possible to identify, on the basis of crash severity rate, the 100 best-performing and 100 worst-performing expressway intersections. With these 200 intersections, a statistical analysis was completed to determine the effects intersection design and surrounding land use have on an intersections safety performance. Skewed intersections, intersections located on vertical or horizontal curves, and intersections at which there is varying surrounding land use were studied to determine their effects on safety performance. Following the completion of the analysis of the 200 intersections, the 30 intersections with the highest crash severity index rates were selected for more thorough, site-specific analysis. As part of this analysis, the authors examined the impact of land use adjacent to the intersection and of peaking in hourly traffic volumes. The research identifies attributes that impact crash frequency and severity both negatively and positively.

Impact of 65-mph Speed Limit on Iowa's Rural Interstate Highways: Integrated Bayesian Forecasting and Dynamic Modeling Approach

In 1987, a provision of the Surface Transportation and Uniform Relocation Assistance Act allowed states to raise speed limits on rural Interstates to 65 mph (104.6 km/h). By 1995, nearly all states had done so. Several studies have investigated the safety impacts of these increases. Methodologies varied from analysis of variance to simple before and after comparison and have included time series procedures, with and without intervention variables. In general, these studies have produced contradictory findings. An integrated Bayesian forecasting and dynamic modeling approach used to determine the impact of the increased speed limit on rural Interstates of Iowa is reported. The approach is used to verify that raising the speed limit to 65 mph (104.6 km/h) led to an increase in fatal accidents on rural Interstates of Iowa. Comparison of fatal accident data on rural Interstates of Iowa and New Jersey yields similar results. Although this conclusion was anticipated, the study further demonstrates that a Bayesian/dynamic approach is more robust than the standard time series model.

Freight planning typology

A layered architecture for freight transportation demand modeling entails the construction of a statewide freight transportation demand model by separately simulating traffic for one commodity at a time. Layers can then be added together to construct a comprehensive model that includes the most significant freight flows. Most state or regional economies are dominated by a few economic sectors, and models can be constructed for those sectors that generate the most freight traffic and/or are the most important to the regional economy. Freight traffic demand modeling in intercity applications is more likely to focus on economic development, local infrastructure improvements, maintenance, and similar policy and planning concerns than on system capacity issues. Thus, it is more important to understand changes in traffic growth by economic sector than as the composite of all freight traffic. This method is less data intensive and more easily understood by transportation professionals than previous approaches. The layered approach is therefore more likely to achieve the desired objectives than would general models, which attempt to forecast heterogeneous freight transportation demands simultaneously. This approach is demonstrated through a case study using the meat products and farm machinery industries in Iowa. Other commodities will be added in the future to complete a model of Iowa’s statewide freight transportation demand. A framework is presented for organizing and identifying planning goals, key issues, and predominant commodities for intercity freight transportation. Although examples are provided, specific recommendations addressing the full range of issues, data collection activities, tools, and urban applications are suggested for further study. A case study demonstrates the approach used for one issue, one mode, and two commodities, which could be repeated elsewhere for similar applications.

Integrated Approach to Pavement Marking Management

Providing good pavement marking performance is an essential component of the transportation system. According to Tom Welch, state safety engineer for the Iowa Department of Transportation (DOT), “Every older driver forum has included a consistent demand for brighter and more durable pavement markings.” This paper summarizes some management tools developed for Iowa DOT as part of a pavement marking management system (PMMS). A summary of how retroreflectivity data are used statewide in managing pavement marking performance is provided as well as a discussion of how the PMMS was integrated with other infrastructure management resources for Iowa DOT.

Safety Effectiveness of Stop Control at Ultralow-Volume Unpaved Intersections

Establishment of the proper level of traffic control on low-volume rural roads can be problematic for local agencies. Ten years of crash data for more than 6,000 rural, unpaved intersections in Iowa were analyzed, with stop-controlled intersections compared with uncontrolled intersections. Crash models were developed with logistic regression and hierarchical Poisson estimation. For ultralow-volume intersections, those used by fewer than 150 vehicles per day, results indicated no statistical difference in the safety performance of each level of control. The effect of excessive use of control on safety performance also was tested for rural and urban applications, with no detrimental effect generally being indicated.

Optimum Urban Clear Zone Distance

Urban communities often have limited amounts of right-of-way available for establishing a setback distance from the curb for fixed objects. Urban road designers must weigh the cost of purchasing additional right-of-way for clear zones against the risk of fixed-object crashes. From 2004 to 2006, fixed-object crashes made up 15% of all fatal urban crashes and 3% of all crashes in the state of Iowa. Many states use AASHTO recommendations as minimum clear zone standards, whereas other states have increased the required minimum clear zone distance, but little research exists to support the specification of these minimums. The effects of the clear zone on safety performance of urban curbed streets were studied. The study included synthesizing selected state practices and investigating the benefits of various clear zone widths on the basis of 13 urban corridors in Iowa. The results suggest that a 4- to 5-ft clear zone could be effective in reducing 90% of urban fixed-object crashes and recommend that additional research be conducted to account for variations in speed, traffic, and other corridor characteristics.

Strategy Implementation by State Transportation Agencies to Maintain Work Zone Mobility and Safety

Mitigation strategies for work zone congestion are used by transportation agencies to manage or reduce congestion through a work zone as part of the projects transportation management plan. The objective of this research is to assist agencies’ strategy selection by identifying strategies used by state transportation agencies (STAs) nationwide and their experiences. An online survey was developed to identify current, past, and future strategy implementation for projects similar to four developed scenarios: rural reconstruction, rural resurfacing, urban reconstruction, and urban resurfacing projects. The survey received 42 responses from individuals representing 28 states (responses were received from multiple districts or regions from a few states). It was found that agencies used several strategies to address different aspects of mobility and safety. Strategy selection varied between facility location and work activity. STAs also provided strategies that failed to meet expectations and identified strategies their agency plans to implement in the future. Based on the survey results and gaps in current literature, recommendations for strategy selection and future research are provided.

Dedicated Truck Facilities as Solution to Capacity and Safety Issues on Rural Interstate Highway Corridors

This paper identifies the safety and operational benefits of constructing dedicated truck facilities on a rural Interstate corridor. The Interstate highway segment in the case study is a 164-mi section of I-80 from the Iowa–Illinois border to Altoona, Iowa (an eastern suburb of Des Moines, Iowa). Although many studies have considered constructing an additional lane on freeways and designating it for trucks only, this paper considers the construction of a separate four-lane, limited-access facility for trucks. The I-80 corridor was analyzed with the Highway Economic Requirements Software–state edition (HERS-ST) to measure the performance before and after trucks were removed from the general purpose lanes. Several benefit-to-cost ratios were calculated outside of HERS-ST to determine the economic feasibility (but not the financial feasibility) of constructing dedicated truck lanes. Since there are no similar truck-only facilities in the United States, it is unknown what proportion of motor carriers would choose to use a truck-only facility rather than the mixed-traffic lanes (general purpose lanes), and future policy may or may not require trucks to use parallel truck-only facilities. Therefore, a sensitivity analysis was conducted within the benefit-to-cost analysis to determine the benefits of diverting 100%, 75%, 50%, and 25% of trucks to a dedicated truck facility. At all levels of diversion, the benefits exceed the costs. Although the analysis shows that a truck-only facility is desirable, the policy framework to make such a facility physically and financially feasible does not exist in federal or Iowa policy.

Part 3: Pavement Markings: Integrated Approach to Pavement Marking Management

Providing good pavement marking performance is an essential component of the transportation system. According to Tom Welch, state safety engineer for the Iowa Department of Transportation (DOT), Every older driver forum has included a consistent demand for brighter and more durable pavement markings. This paper summarizes some management tools developed for Iowa DOT as part of a pavement marking management system (PMMS). A summary of how retroreflectivity data are used statewide in managing pavement marking performance is provided as well as a discussion of how the PMMS was integrated with other infrastructure management resources for Iowa DOT.