<rss version="2.0" xmlns:atom="https://www.w3.org/2005/Atom">
  <channel>
    <title>Transport Research International Documentation (TRID)</title>
    <link>https://trid.trb.org/</link>
    <atom:link href="https://trid.trb.org/Record/RSS?s=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" rel="self" type="application/rss+xml" />
    <description></description>
    <language>en-us</language>
    <copyright>Copyright © 2026. National Academy of Sciences. All rights reserved.</copyright>
    <docs>http://blogs.law.harvard.edu/tech/rss</docs>
    <managingEditor>tris-trb@nas.edu (Bill McLeod)</managingEditor>
    <webMaster>tris-trb@nas.edu (Bill McLeod)</webMaster>
    <image>
      <title>Transport Research International Documentation (TRID)</title>
      <url>https://trid.trb.org/Images/PageHeader-wTitle.jpg</url>
      <link>https://trid.trb.org/</link>
    </image>
    <item>
      <title>Update of Intersection/Interchange Guidelines for Rural Expressways in Nebraska</title>
      <link>https://trid.trb.org/View/2703929</link>
      <description><![CDATA[Nebraska Department of Transportation (NDOT) staff frequently decide on changes to existing two-way stop-controlled (TWSC) intersections on rural expressway to alternative facilities, such as a restricted crossing U-turn (RCUT), a roundabout, a signalized intersection, or an interchange. As Nebraska makes progress toward completion of its expressway system, updated and defensible decision-making is essential for conversion of TWSC highway intersections. NDOT’s existing guidelines, developed in the 1990s, no longer reflect current operations, safety performance, or modern intersection designs. This project updated and expanded NDOT’s guidance using contemporary traffic operational and safety data, combined with robust microsimulation and safety performance modeling. Traffic operations data were collected from TWSC, RCUT, roundabout, and signalized intersections on rural Nebraska expressways, as well as from diamond interchanges with stop-controlled and signalized ramps and a diverging diamond interchange. These facilities were modelled in a microsimulation environment calibrated to Nebraska driving behavior, generating more than 11,500 scenarios covering a wide range of major road, minor road, and ramp volumes, turning combinations, and time-of-day conditions. The simulation results were used to develop statistical models for estimation of operational delays and predictions of the most suitable intersection/interchange alternatives. Safety analysis incorporated crash data from TWSC intersections along rural expressways to develop a negative binomial model for estimation of crash frequencies across different traffic scenarios. The safety performances of alternative at-grade facilities were estimated using appropriate crash modification factors. This study used the Federal Highway Administration (FHWA) “Interchange Comparison Safety Tool” to estimate crash frequency at conventional diamond and diverging diamond interchanges. Furthermore, the research team compiled construction and retrofit cost information from national sources and Nebraska-specific projects for a comprehensive benefit-cost analysis. The resulting guidelines integrated benefit-cost outcomes with operational and safety analyses, engineering judgment, and national best practices. These data-driven guidelines provide NDOT with a modern, consistent, and defensible framework for evaluating intersection upgrades, selecting interchange types, and assessing grade-separation needs on Nebraska’s rural expressways.]]></description>
      <pubDate>Thu, 28 May 2026 16:15:52 GMT</pubDate>
      <guid>https://trid.trb.org/View/2703929</guid>
    </item>
    <item>
      <title>Traffic conflict characteristics and evolution mechanism in freeway weaving segments with varying spacing</title>
      <link>https://trid.trb.org/View/2701556</link>
      <description><![CDATA[With the rapid expansion of China’s freeway network and the increasing density of interchange clusters, reduced interchange spacing has emerged as a critical challenge for weaving section safety. To systematically characterize how spacing affects the distribution, severity, and duration of traffic conflicts in weaving areas, this study collected aerial video data from four weaving sections with spacing of 400 m, 600 m, 850 m, and 1400 m along the Changhu Freeway in Dongguan. Using the Data from Sky video analysis platform for trajectory extraction and time-to-collision (TTC)-based surrogate safety analysis, the spatiotemporal evolution of traffic conflicts under varying spacing conditions was investigated. The research demonstrates that spacing is a critical factor influencing conflict risk. Reduced spacing exacerbates risk through spatial compression effects, manifested by a leftward shift of the primary TTC distribution peak, reduced collision avoidance time, and a significant increase in both the proportion of critical conflicts and TET duration. In contrast, longer spacing (850 m and 1400 m) provides necessary buffer space, optimizes conflict distribution, and reduces severity. The weaving flow ratio shows a positive correlation with the unit conflict rate. The 850 m scenario exhibits the highest conflict rate due to its combination of high traffic volume and high weaving flow ratio; however, conflict severity remains primarily regulated by spacing. Conflicts between heavy vehicles (L-L) present the highest risk, with a mean TTC of only 2.3 s and a critical conflict proportion of 18.53%, while light vehicle combinations (S-S) perform optimally. Vehicle movement intentions also significantly influence conflict characteristics: combinations with shared intentions (S-S, F-F, H-H) exhibit elevated risks due to high trajectory overlap, and their conflict numbers show an increasing trend under longer spacing. In contrast, heterogeneous vehicle combinations (S-F, S-H) are less affected by spacing variations. Based on these findings, a minimum spacing of 850 m is recommended as a practical safety threshold for weaving section design, and vehicle-type-specific management measures are advised for constrained sections below this benchmark. The findings of this study can provide a theoretical foundation and practical guidance for the planning, design, and management of weaving sections in freeway interchanges.]]></description>
      <pubDate>Wed, 27 May 2026 10:48:49 GMT</pubDate>
      <guid>https://trid.trb.org/View/2701556</guid>
    </item>
    <item>
      <title>Collaborative Multi-Lane Scheduling Strategy for Connected and Automated Vehicles on Highway Interchange Using Rolling Traversal Scheduling</title>
      <link>https://trid.trb.org/View/2646686</link>
      <description><![CDATA[With the rapid development of transportation infrastructure, highway interchanges have become critical nodes in the network, where congestion frequently occurs. Existing research on congestion mitigation in such regions is limited, often focusing on individual bottlenecks, which may overlook interactions between diverging and merging areas. Some other research adopted a macroscopic traffic flow perspective, without microscopically mitigating right-of-way conflicts caused by lane-changing demands of vehicles. To address this gap, this study proposes a collaborative multi-lane scheduling strategy for connected and automated vehicles under a cloud control system. By jointly optimizing vehicle passing sequences in both diverging and merging zones, the proposed method aims to improve overall traffic efficiency. Key contributions include a rolling traversal mechanism for global scheduling, a discretionary lane-changing strategy for enhanced lane utilization, and a double-checked trajectory planning approach that balances efficiency and comfort. This framework offers a scalable solution to alleviate congestion at complex highway interchanges under high traffic demand.]]></description>
      <pubDate>Mon, 18 May 2026 16:36:43 GMT</pubDate>
      <guid>https://trid.trb.org/View/2646686</guid>
    </item>
    <item>
      <title>Evaluation of Alternative Intersection and Interchange Options for Nebraska </title>
      <link>https://trid.trb.org/View/2689408</link>
      <description><![CDATA[The Nebraska Department of Transportation (NDOT) has implemented and developed guidance for a limited set of unconventional designs (e.g., certain RCUTs and diverging diamond interchanges) and has accumulated experience through selected projects and research studies. NDOT lacks robust, Nebraska-specific tools to: (1) screen and select candidate unconventional facilities; (2) quantify trade-offs in operations, safety, and cost; and (3) develop practical guidelines that can be directly used by designers, planners, and district staff. This gap creates uncertainty when considering unconventional options and may limit NDOT’s ability to fully leverage designs that could offer meaningful safety and mobility benefits. The proposed research will provide NDOT with a structured and evidence-based approach for identifying the most suitable unconventional intersection and interchange options for Nebraska. By evaluating both the designs already implemented within the state and additional alternatives that may be considered soon, the study will broaden NDOT’s understanding of how various unconventional treatments perform under different traffic, geometric, and environmental conditions in Nebraska.]]></description>
      <pubDate>Tue, 02 Jun 2026 12:26:34 GMT</pubDate>
      <guid>https://trid.trb.org/View/2689408</guid>
    </item>
    <item>
      <title>Safety and Operational Performance Assessment of CFIs and DDIs in Utah</title>
      <link>https://trid.trb.org/View/2632836</link>
      <description><![CDATA[This research project will assess the safety and operational performance of Continuous Flow Intersections (CFIs) and Diverging Diamond Interchanges (DDIs) in Utah. The study will develop Utah-specific Safety Performance Functions (SPFs), Crash Modification Factors (CMFs), and Adjustment Factors (AFs), using Utah Department of Transportation (UDOT) data resources and advanced analytical techniques including statistical modeling, machine learning, and computer vision. The findings will support updates to UDOT design guidelines and planning tools such as CAP-X, SPICE, and ICE.]]></description>
      <pubDate>Thu, 27 Nov 2025 08:54:32 GMT</pubDate>
      <guid>https://trid.trb.org/View/2632836</guid>
    </item>
    <item>
      <title>Evaluating the Economic and Safety Trade-offs of Interchange and Access Drive Separation Distances
</title>
      <link>https://trid.trb.org/View/2627344</link>
      <description><![CDATA[The research project will evaluate whether the Iowa Department of Transportation’s (Iowa DOT) minimum separation standards between interchanges and first access points are overly restrictive and potentially detrimental to development opportunities around those interchanges. To achieve this, the project will utilize deep learning techniques to analyze high-resolution aerial photographs to identify interchanges on state-owned roadways, their first driveway access points, and the specific aspects of development status, such as the presence of commercial or residential buildings, vacant land, or agricultural use of the surrounding land. Crash data from the Iowa dataset will be examined to assess safety outcomes about these separation distances. A critical part of the analysis will involve evaluating the economic potential of these lands and estimating the impact of separation standards on land utilization and potential economic growth. 
In addition to state-owned interchanges, the study will identify non-interchange intersections with roadways with similar AADT levels, the number of lanes, if a median is present, and other relevant geometric features to access management. The closest access point will be determined for these intersections, mirroring the approach taken with the interchanges. The crash history for these locations will be retrieved to compare the safety performance of interchanges and non-interchange intersections directly.
This analysis, focusing on interchange and access point separation distances, will help isolate the effect of these separation standards on safety and development, controlling for traffic volume and other features. By examining interchange and non-interchange sites under similar conditions, the research will determine if the minimum separation distances at interchanges are justified or could be adjusted to better balance safety with economic development, potentially informing future policy decisions. The research will also determine the amount of developable land that could be available should the standards be relaxed.
]]></description>
      <pubDate>Wed, 19 Nov 2025 14:36:56 GMT</pubDate>
      <guid>https://trid.trb.org/View/2627344</guid>
    </item>
    <item>
      <title>Develop a Data-Driven Intersection &amp; Interchange Control Evaluation (DIICE) Tool</title>
      <link>https://trid.trb.org/View/2614516</link>
      <description><![CDATA[Innovative intersection and interchange designs and smart technologies (e.g. adaptive traffic signal systems, connected vehicle technology, and real time traffic management) are often considered as methods to reduce congestion and promote safety. However, these designs are challenging and time-consuming to consider for a given project. The research team will develop a data-driven innovative design recommendation tool to provide guidance toward feasible design selections of innovative intersections and interchanges. The tool will be applicable in urban settings and consider factors like traffic volumes, safety enhancements, constructability, pedestrian and bicyclist accommodations, and costs. The tool will be complimented by guidance gathered from the literature and stakeholder interviews to help provide context and considerations that cannot be incorporated into the too. This will promote a consistent solution to aid in the intersection design selection process that can be used to reduce costs for considering innovative intersections and can be presented to policymakers as a data-driven recommendation. The research team will vet this prototype tool by applying the tools to existing innovative intersection/interchange design selections within Texas to demonstrate the effectiveness of the design selection solution.]]></description>
      <pubDate>Tue, 28 Oct 2025 11:20:20 GMT</pubDate>
      <guid>https://trid.trb.org/View/2614516</guid>
    </item>
    <item>
      <title>Crash risk associated with eyes-off-road duration by road control type and intersection type</title>
      <link>https://trid.trb.org/View/2522085</link>
      <description><![CDATA[Scanning the driving environment is crucial for safe driving. However, the complexity of the driving environment affects a driver’s ability to maintain sufficient situational awareness. This study aimed to quantify the crash risk associated with eye-off-road (EOR) behavior across different road control and intersection types, providing insights for Driver Monitoring Systems (DMSs). Using data from the Second Strategic Highway Research Program Naturalistic Driving Study (SHRP 2 NDS), the authors analyzed crash risk associated with EOR glance durations within a 6-second window. The authors compared odds ratios across three EOR duration groups: ≤ 2 s, 2 to 3 s, and 3 to 4 s. Additionally, the authors used a General Additive Model (GAM) to explore the non-linear relationship between EOR duration and crash risk.  The findings reveal that crash risk is higher on uncontrolled access roads compared to controlled access roads. Among intersection types, turning at intersections presents the highest risk, followed by going straight at intersections and driving on straight non-intersection segments. Notably, the crash risk increases linearly only for short EOR durations but rises much faster than linearly when EOR durations exceed specific thresholds: 1.3 s for controlled access roads, 1.2 s for uncontrolled access roads, and as low as 0.9 s for turning at intersections. These results challenge the commonly used 2-second threshold in driver distraction research, offering more refined insights that could enhance DMS alert settings based on driving environment. This study underscores the importance of considering road and intersection types when assessing the risks of EOR behavior, contributing to improved road safety strategies. Note that the study is not intended to specify exact values for DMS timers, which must be determined in practice by considering multiple factors. Additionally, the false alert rate requires further evaluation.]]></description>
      <pubDate>Wed, 23 Apr 2025 16:10:48 GMT</pubDate>
      <guid>https://trid.trb.org/View/2522085</guid>
    </item>
    <item>
      <title>Assessment of Safety and Operation Performances of CFIs and DDIs in Utah</title>
      <link>https://trid.trb.org/View/2394799</link>
      <description><![CDATA[Alternative intersection and interchange designs, such as the Diverging Diamond Interchange (DDI) and the Continuous Flow Intersection (CFI), have garnered significant attention among transportation agencies, researchers and practitioners over the past 15 years, due to their ability to improve operations and safety of transportation systems. The Utah Department of Transportation (UDOT) is recognized as a national leader in the design and implementation of innovative intersections and interchanges. Currently there is not a lot of information on field-based performance measures of these designs. As it has been 16 years since the first CFI was implemented, followed by many more CFIs and DDIs, UDOT's databases contain a lot of useful data regarding operations and safety of these designs. The accelerated deployment of DDIs and CFIs necessitates the needs for more in-depth assessment of their benefits and impacts. The objective of this study is to perform safety and operational assessment of CFIs and DDIs in Utah. It will develop Utah-specific Safety Performance Functions (SPFs) and Crash Modification Factors (CMFs) for these designs. The study will also assess the operational performance of CFIs and DDIs, and explore ways in which operations can be improved (geometry, control, signalization).]]></description>
      <pubDate>Thu, 20 Jun 2024 16:23:48 GMT</pubDate>
      <guid>https://trid.trb.org/View/2394799</guid>
    </item>
    <item>
      <title>A Guide on Alternative Intersections and Interchanges


</title>
      <link>https://trid.trb.org/View/2381742</link>
      <description><![CDATA[Alternative intersection and interchange (AII) designs initially emerged as a way to improve safety and operations while reducing project costs and impacts, with the potential to enhance facilities for pedestrians and bicyclists.

Early consideration and implementation by agencies were supported by the Federal Highway Administration (FHWA) Alternative Intersections/Interchanges Informational Report and a series of informational guides published since 2014. More recently, the North Carolina Department of Transportation (DOT) released an annotated outline for an updated informational report, and FHWA published a new guide focused on pedestrian and bicyclist safety at alternative intersections. Additionally, recent NCHRP reports provide detailed guidance on roundabouts, multimodal safety at alternative intersections, and intersection control evaluation.

Research is needed to develop a guide on several widely adopted intersection types, reflecting the growing knowledge and experience from successful implementations by many DOTs. The guide also will focus on expanding the toolbox of AII types and options to help DOTs enhance multimodal transportation safety and operational efficiency.

The objective of this research is to develop a guide to support state DOTs and other transportation agencies in considering AIIs in their project planning and development process. The guide will consist of two parts: (Part I) will provide comprehensive information on U-turn-based intersections, covering key issues related to planning, implementation, operation, and maintenance; and (Part II) will provide an expanded resource on AIIs, focusing on the efficacy of underutilized, emerging, or new concepts, as well as their variations.]]></description>
      <pubDate>Wed, 22 May 2024 12:59:54 GMT</pubDate>
      <guid>https://trid.trb.org/View/2381742</guid>
    </item>
    <item>
      <title>Construction Inhibitors of Alternative Intersections and Interchanges</title>
      <link>https://trid.trb.org/View/2353119</link>
      <description><![CDATA[The use of alternative intersections and interchanges (AII) is crucial for transportation infrastructure because AII enhances traffic flow, increases capacity and safety, and accounts for future traffic demands. One challenging problem is that AII designs are negatively perceived in the construction industry since they are perceived to result in additional construction time and cost compared to projects with conventional designs. To assess this concern, the identification of construction inhibitors affecting AII projects was investigated using claims and supplemental agreement data using AIIs and conventional design projects. Findings indicated inhibitors that most affected project performance and top five inhibitors were utilities, additional work, work delays, safety for workers, and weather impacts. By understanding the potentially negative impact of these inhibitors, the constructability of AII projects can be enhanced, and transportation agencies can opt for more sustainable solutions.]]></description>
      <pubDate>Mon, 20 May 2024 14:02:20 GMT</pubDate>
      <guid>https://trid.trb.org/View/2353119</guid>
    </item>
    <item>
      <title>Crashes Related to Type and Location of Driveway Access</title>
      <link>https://trid.trb.org/View/2368966</link>
      <description><![CDATA[This study examines how commercial driveway access location and design interact with roadway and interchange characteristics to influence vehicular, bicycle, and pedestrian safety. The final sample for analysis included: a) 192 roadway segments with 9,889 commercial driveways and 10,596 driveway-related crashes; and b) 69 interchanges with 832 commercial driveways and 853 driveway-related crashes in the vicinity of the interchanges. Several analytical methods were used to assess the safety effects of driveway type and location on crash type and severity, including summary statistics and statistical analysis, generalized linear modeling techniques, and exploratory case studies. Results indicated that both non-traversable medians and Two-Way Left-Turn Lanes (TWLTLs)  decrease the overall crash frequency at commercial driveways along corridors compared to undivided or painted medians. Exclusive right-turn lanes at commercial driveways were found to reduce the average number of driveway-related crashes near interchanges by 49.7% compared to shared right-turn lanes, and by 64.0% compared to no right-turn lanes. Shared right-turn lanes also significantly reduced the probability of severe injury and fatality crashes by 35.3% at commercial driveways along corridors. Both sufficient driveway throat length and driveway channelization were found to improve commercial driveway safety. Unsignalized or signalized commercial driveways located less than 500 ft from the end of the interchange ramp taper increased the potential for severe injury crashes by 261%. Conventional bike lanes appeared to induce pedestrian/bicycle crashes at or near commercial driveway locations, possibly due to the potential for motor vehicles to encroach into the bike lane and/or overlook bicyclists when crossing bike lanes to enter or exit commercial driveways. Conventional bike lanes were also found to significantly increase the risk of minor injury crashes at commercial driveways near interchanges. Therefore, when a bike lane is needed on a major roadway, buffered bike lanes or other types of physical barriers should be used when feasible, as well as bike lane paint at driveway locations to further alert motorists of the presence of bicyclists. Case study analysis further revealed that a variety of conflicts and crashes occur when aligning high-volume commercial driveways at full median openings without signal control. Crash clusters were also observed at driveways in the functional area of signalized intersections and interchanges. A contributing factor identified in crash reports was a tendency for “good Samaritans” to allow drivers entering or exiting driveways on multilane roadways to blindly cross one or more lanes of queueing traffic. Suggestions are offered for consideration by Florida Department of Transportation (FDOT) and other agencies relative to commercial driveway access policy, permitting and mitigation to improve roadway and interchange area safety.]]></description>
      <pubDate>Mon, 22 Apr 2024 09:39:12 GMT</pubDate>
      <guid>https://trid.trb.org/View/2368966</guid>
    </item>
    <item>
      <title>Guidelines to Enhance the Constructability of Diverse, Modern, and Unconventional Intersections and Interchanges (DMUII)</title>
      <link>https://trid.trb.org/View/2359112</link>
      <description><![CDATA[The current focus on promoting sustainability in the United States transportation infrastructure has led to adopting Diverse, Modern, and Unconventional Intersections and Interchanges (DMUII) to improve traffic flow while ensuring safety. However, the adoption of DMUII designs presents challenges, including a learning curve for the public and contractors and additional time and cost compared to conventional Intersection and Interchange (CII) designs. This research aims to identify and mitigate the inhibitors that hinder DMUII design and construction while addressing critical questions related to constructability and cost-effectiveness. To achieve these goals, multiple studies were conducted to identify inhibitors and strategies to overcome them. The identified inhibitors affecting DMUII projects were validated using four approaches that include the use of data from interviews, surveys, findings from field observations, and evaluation of claims and supplemental agreements. Additionally, a case study evaluating roadway congestion and detour operations resulting from Work Zone Traffic Control measures was undertaken, revealing the complexities of DMUII and CII projects and their implications on travel time, roadway congestion, and road user costs. Through this research, effective methods to enhance DMUII constructability were identified and these include constructability reviews, modularization, prefabrication for bridge construction, automation, staging, and 3D/4D modeling. Findings were compiled in the form of lessons learned and best practices obtained which provide valuable insights for formulating construction strategies, facilitating the construction of DMUIIs, and addressing traffic volume challenges while ensuring safety. These findings can be implemented by transportation departments seeking to optimize DMUII performance and contribute to more sustainable transportation infrastructure.]]></description>
      <pubDate>Thu, 11 Apr 2024 13:23:20 GMT</pubDate>
      <guid>https://trid.trb.org/View/2359112</guid>
    </item>
    <item>
      <title>Traffic Analysis Tools: Assessment, Comparison and Validation Study</title>
      <link>https://trid.trb.org/View/2265655</link>
      <description><![CDATA[This report summarizes the findings of a research project aimed at assessing the accuracy of both analytical and microsimulation tools in describing the operational performance of a variety of intersection and interchange types under North Carolina conditions. The three tools evaluated in this study were SYNCHRO10, SIDRA9 and Trans Modeler5. In addition, some basic comparisons with the Federal Highway Administration (FHWA) CAP-X sketch planning tool was carried out for some sites. The original, Pre-Covid scope of work was to cover ten congested interrupted flow facilities in the field. The revised scope reduced the field effort to six sites, including an isolated and coordinated signalized intersection; a single lane roundabout; a traditional diamond interchange; an offset intersection and a continuous flow intersection (CFI) with an additional two alternative intersection (AI) sites (Diverging Diamond Interchange and a Reduced Conflict Intersection) processed via a sensitivity analysis to variations in demand volumes, capacity and control conditions. The team carried out all fieldwork using high-resolution videos taken from one or two drones at a height of 300-400 ft., supplemented with ground based cameras and Blue Tooth units as needed. All video data were then post-processed via a third party vendor, Data From Sky (DFS). The processed videos enabled the team to generate individual vehicle ID’s and their position, in the field of view. Subsequently the field data produced multiple performance measures at the point, segment and facility levels. Five of the field sites, located in five different NC counties, involved signalized intersections. Measurements of saturation flow rates at those sites produced values that were below expectations, in the range of 1,520-1,770 pc/hr./lane. This is likely to be generating lower movement capacities than are currently being assumed in NC modeling studies. These rates were needed for model calibration in this study for both Synchro and SIDRA. In the case of Trans Modeler microsimulation, saturation flow rates are entered using a headway buffer parameter. The research has developed a graphical plot relating the buffer value and saturation flow rate, which can be used to calibrate the input for a specific saturation flow rate value. In general, when field conditions were operating in the level of service (LOS) range A-C, all three models generated performance measures (PMs) that were close to each other and to the field value. However, under congested conditions, the analytical models tended to overestimate the field PMs, while the microsimulation model tended to slightly underestimate them. Part of the problem is related to the presence of initial and final queues in estimating the true traffic demand volumes (as opposed to the discharge flow rate in traditional traffic counts). The team recommends the use of a microsimulation model in those cases, with due attention to including the initial queue effects on delays. Another limitation discovered in both SIDRA and SYNCHRO (and HCM6) was their inability to generate correct Origin Destination based LOS measures in the field at both the CFI and offset intersections. The team was able to generate an alternative analytical approach that was validated at both those sites. Finally, the team also developed a new methodology for the field estimation of the critical headway value for roundabouts in Trans Modeler, which is explained in detail in Chapter 4 of this report. Additional work is needed to further develop the analytical approach for application to all alternative intersection cases.]]></description>
      <pubDate>Thu, 19 Oct 2023 09:31:02 GMT</pubDate>
      <guid>https://trid.trb.org/View/2265655</guid>
    </item>
    <item>
      <title>Assessing Safety Performance of Atypical Service Interchanges

</title>
      <link>https://trid.trb.org/View/2219016</link>
      <description><![CDATA[Many service interchanges include custom designs that do not fit into the traditional interchange definitions contained within the American Association of State Highway and Transportation Officials (AASHTO) Green Book, which makes it challenging to forecast and compare the relative predicted crash frequency of various atypical service interchanges. While the Highway Safety Manual (HSM) provides crash prediction for interchange elements such as basic ramps and ramp termini configurations, it does not offer a comprehensive crash prediction methodology applicable to such atypical service interchanges.

Atypical service interchanges lack a one-size-fits-all safety assessment method due to their uniqueness and complexities. To address this, engineers envision a "building-block" approach to deconstruct these interchanges into fundamental elements, e.g., ramp geometries, configurations, termini, weave segments, merge and diverge areas, access points and connections to managed lanes, active transportation, and transit facilities. This could involve assessing safety performance functions (SPFs) as well as crash modification factors (CMFs) for each element, and then aggregating these assessments to form a comprehensive analysis. However, such a generalized method is not currently available for engineers to analyze the safety performance of atypical service interchanges. 

Research is needed to apply conflict or exposure-based methods specifically tailored to these atypical service interchanges, analyzing each fundamental element, and then integrating the results from individual safety performance analyses into a comprehensive final result.

The objective of the project is to develop a method to partition interchanges into fundamental elements; analyze, quantify, and assess the safety performance of each element; and develop customized SPF models that will integrate the results from individual safety performance analyses into a comprehensive final result for atypical service interchange designs. 
]]></description>
      <pubDate>Tue, 25 Jul 2023 08:09:40 GMT</pubDate>
      <guid>https://trid.trb.org/View/2219016</guid>
    </item>
  </channel>
</rss>