A Practical Approach to Safety management of County Roads

Rural roads are well-documented as having a greater traffic fatality rate than urban roads. For medium- and high-volume rural roads with a considerable crash history, previous studies have focused on the identification of high-crash locations. The majority of rural roads in Indiana are low-volume county roads. However, the methods for identifying safety problems on medium- and high-volume roads are often not suitable for county roads. Such methods may result in improper allocation of resources for safety upgrades to only the particular locations which experienced crashes, not necessarily where the crash risk is greatest. For example, there may be hazards on the road right-of-way that have not yet been manifested through crashes, but still represent a considerable risk should they influence the driver’s behavior and/or affect the crash outcome. This study proposes decision-making based on the crash risk and fatality risk on road elements (segments and intersections) estimated from the geometry, pavement, roadside features, and traffic volume (if available). The methodology will be applied to the rural county road network in Tippecanoe County. Once the road elements with the highest risk are identified, the actual crash history will be used to supplement the analysis. The outcome of this study will be implemented as a project-oriented safety management tool for county roads. This approach will identify low-cost safety countermeasures applied to multiple roadway elements which will provide the most benefits under limited resources. The proposed approach will make economic justification of safety improvements on county roads easier than the current method based on high-crash locations

A Practical Approach to Safety Management of County Roads

Rural roads are well-documented as having a greater traffic fatality rate than urban roads. For medium- and high-volume rural roads with a considerable crash history, previous studies have focused on the identification of high-crash locations. The majority of rural roads in Indiana are low-volume county roads. However, the methods for identifying safety problems on medium- and high-volume roads are often not suitable for county roads. Such methods may result in improper allocation of resources for safety upgrades to only the particular locations which experienced crashes, not necessarily where the crash risk is greatest. For example, there may be hazards on the road right-of-way that have not yet been manifested through crashes, but still represent a considerable risk should they influence the driver’s behavior and/or affect the crash outcome. This study proposes decision-making based on the crash risk and fatality risk on road elements (segments and intersections) estimated from the geometry, pavement, roadside features, and traffic volume (if available). The methodology will be applied to the rural county road network in Tippecanoe County. Once the road elements with the highest risk are identified, the actual crash history will be used to supplement the analysis. The outcome of this study will be implemented as a project-oriented safety management tool for county roads. This approach will identify low-cost safety countermeasures applied to multiple roadway elements which will provide the most benefits under limited resources. The proposed approach will make economic justification of safety improvements on county roads easier than the current method based on high-crash locations

Performance Assessment of Road Barriers in Indiana

Road barriers have been used as an effective countermeasure to prevent exposure of errant vehicles to both vehicles travelling in the opposite direction and to roadside hazards. The objective of this study was to evaluate the in-service safety performance of three types of road barriers (concrete barriers, steel W-beam guardrails, and high-tension cable barriers) in Indiana using cross-sectional analysis based on crash data. The quantitative evaluation was comprised of three components: 1) the effect of the road, barrier scenarios, and traffic on the barrier-relevant (BR) crash frequency, 2) the effect of the road and the barrier scenarios on the BR harmful events, and 3) the effect of the BR events and other conditions on the injury outcomes. The introduction of the BR harmful events linked the crash onset with its outcome. The three developed statistical models were connected through their inputs-outputs and followed the sequence of various BR events during the BR crash. This improvement allowed a more comprehensive and insightful analysis of the barriers’ safety effects and a more efficient use of data. The injury outcomes were estimated for all the individuals in a crash rather than for the most severe outcome of a crash. Further improvement of the cost estimates was accomplished by utilizing hospital data. For median barriers, this study found that the total number of BR crashes was higher with the use of median barriers, mostly due to the introduction of collisions with barriers and an increase in the collisions after redirecting vehicles back to traffic. These undesirable effects of barriers were surpassed by the positive results of reducing hazardous events such as cross-median crashes, rollover events, and collisions with roadside hazards, which substantially reduced the number of severe injuries and fatalities. The average (unit) crash costs were estimated for roads without barriers and for roads with various barrier scenarios. The crash costs were reduced by 50% where cable barriers were in medians wider than 50 feet and where concrete barriers or guardrails were in medians less than or equal to 50 feet wide. Roadside barriers (guardrails) reduced the unit crash costs by 20% to 30%. Median cable barriers were found to be the most effective among all the studied barriers due to the smallest increase in the crash frequency and least severe injuries in barrier-relevant crashes. A cable barrier’s offset to the travelled way was also investigated in this study. When considering vehicles moving in one direction, the nearside cable barriers installed at an offset less than or equal to 30 feet performed better than far-side cable barriers with a larger offsets thanks to the better protection they provide for vehicles against rollovers in the median and impact with the median drain. Consequently, the biggest safety benefit can be expected where cables barriers are installed in the median at both edges. The results were implemented through a set of crash modification factors and unit crash costs estimated for 51 road-barrier scenarios. An implementation procedure is provided to quantify the crash costs and the safety benefits for these scenarios

SNIP Light User Manual

A systemic approach to identifying road locations that exhibit safety problems was provided by the Safety Needs Identification Program (SNIP and SNIP2) developed by the Purdue University Center for Road Safety (CRS). The new version SNIP Light has been developed to provide other uses with planning level traffic safety analysis capability for a wider range of uses including Metropolitan Planning Agencies (MPOs) who want the tool for planning cost-effective safety programs in their metropolitan areas. The SNIP Light reduces the demand of computing and data storage resources and replaces the SQL server database system an integrated module coded in-house which is considerably faster than the original component. Furthermore, certain proficiency required to install and use the old version is no longer needed thanks to the intuitive single-window interface and executing file operations in the background without the user’s involvement. Some operations, such as optimizing funding of safety projects, are removed to simplify the tool

Safety and Operational Impacts of Alternative Intersections

As the degradation of service at some conventional intersections increases, there becomes a need for alternative solutions other than expensive interchanges. Many alternative intersections have been proposed in the past. Under certain traffic and local conditions some solutions are more promising than other. In some cases, the conventional intersection may still be the optimal choice. The presented research focused on developing guidelines that would help planners and designers identify the most promising solutions for further analysis. This objective has been addresses in two ways. Firstly, the existing knowledge on alternative intersections has been identified. Secondly, the performance of conventional and alternative intersections under a range of Indiana traffic conditions has been evaluated using micro-simulation model - VISSIM. Although a large number of sources could be found on the research subject, the existing knowledge about performance of alternative intersection design is incomplete. Only a few designs proposed in the past have been applied at a considerable number of locations including roundabouts, median U-turns, and jag-handle intersections. Other types still await implementation. The available sources are not comprehensive and deal with conditions that might be different from Indiana. The knowledge of the safety impact of these intersections is very limited. A large number of more than 1,300 scenarios were simulated runs performed with VISSIM calibrated to Indiana conditions. The simulated types of intersections included: conventional, roundabouts, jag-handle near-sided and far-sided, median U-turns, and continuous-flow intersection. Except roundabouts, all other intersections were signalized to test their capacity limits and delay-based performance. Although the roundabouts were the lowest delays at low volumes they also reached the capacity before other did. The most promising solutions for heavy volumes are median U-turns and continuous-flow intersections. The presented research developed guidelines for using alternative intersection designs. The guidelines compile the existing knowledge found in existing publications and research reports with the simulation experiments performed with VISSIM. The guidelines are ready to use and will help planners and designers determine which intersection types are the most promising under considered conditions and should be considered in a detailed way. The simulation results have been summarized in an easy to use format of graphs

Performance Measure That Indicates Geometry Sufficiency of State Highways: Volume I—Project Scoring and Network Screening

The Indiana Department of Transportation (INDOT) selects projects for implementation by taking into account several criteria related to cross-section, alignment and safety to evaluate various geometry improvements to be carried out as a part of projects. The existing practice uses an intuitive point allocation method to score these individual categories. The current study proposes a methodology to evaluate these projects considering the safety and mobility impacts of the improvements which lie in the scope of each project. This methodology is also used to screen roads based on existing geometry deficiencies with respect to a desirable design standard. The road screening process and the project evaluation process form two steps that support the asset management process. The road screening process helps in filtering road segments based on geometry deficiencies and identifies the least adequate road segments. Projects may be further developed with estimated improvements to be carried out on such segments using detailed information regarding these improvements. As part of the study, we have also investigated feasible ways of extracting additional elements from available datasets to support asset management in Indiana. We have looked into available data sources for their suitability. We have combined the use of orthophotos, LiDAR point clouds, digital elevation and surface models to identify remote sensing methods that are capable of extracting the required features efficiently. We propose a framework for determining the paved surface, average grade, embankment slopes, extracting the obstructions near the traveled way like trees and man-made structures

Performance of Alternative Diamond Interchange Forms: Volume 1—Research Report

Service interchanges connect freeways to arterial roads and are the backbone of the U.S. road network. Improving the operations of service interchanges is possible by applying one of several new solutions: diverging diamond, single point interchanges, and double or single roundabout diamonds. VISSIM was used to perform 13,500 experiments to simulate the traffic performance of the studied alternative interchanges during a typical day for a wide range of geometry and traffic scenarios. Five performance measures were investigated: daily-average delay, level of service of critical movement, daily-average number of stops, longest off-ramp queue, and longest crossing road queue. The obtained daily-average delays at the alternative interchanges were consistent with expectations. Roundabouts had the highest average delay while single-point interchanges had the lowest average delays. Roundabouts exhibited the lowest numbers of stops among all the alternatives in the low traffic range up to non-freeway 30,000 veh/day. Diverging diamonds tended to have the shortest and roundabouts tended to have the longest queues on their off-ramps. Overall, single-point interchanges had the shortest queues among all the alternatives. The study developed guidelines for early stage screening of alternative diamond. The guidelines exhibit performance measures for 25 traffic and geometric scenarios and a wide range of traffic volumes. The guidelines provide a fair comparison procedure for alternative diamond interchanges in the preliminary planning and conceptual design stages

Performance of Alternative Diamond Interchange Forms: Volume 2—Guidelines for Selecting Alternative Diamond Interchanges

Service interchanges connect freeways to arterial roads and are the backbone of the U.S. road network. Improving the operations of service interchanges is possible by applying one of several new solutions: diverging diamond, single point interchanges, and double or single roundabout diamonds. VISSIM was used to perform 13,500 experiments to simulate the traffic performance of the studied alternative interchanges during a typical day for a wide range of geometry and traffic scenarios. Five performance measures were investigated: daily-average delay, level of service of critical movement, daily-average number of stops, longest off-ramp queue, and longest crossing road queue. The obtained daily-average delays at the alternative interchanges were consistent with expectations. Roundabouts had the highest average delay while single-point interchanges had the lowest average delays. Roundabouts exhibited the lowest numbers of stops among all the alternatives in the low traffic range up to non-freeway 30,000 veh/day. Diverging diamonds tended to have the shortest and roundabouts tended to have the longest queues on their off-ramps. Overall, single-point interchanges had the shortest queues among all the alternatives. The study developed guidelines for early stage screening of alternative diamond. The guidelines exhibit performance measures for 25 traffic and geometric scenarios and a wide range of traffic volumes. The guidelines provide a fair comparison procedure for alternative diamond interchanges in the preliminary planning and conceptual design stages