RRDs are used to promote early awareness of project results in order to encourage implementation. RRDs also summarize specific findings that emphasize how the research may be used. The contents are organized in terms of the problem and the solution to it, the findings, and the applications. RRDs generally run 4–32 printed pages.
Below are the latest 20 NCHRP Research Results Digests that have been produced by TRB. A page highlighting
that have been released since June 2001 is available online. To search for older publications visit the
NCHRP Research Results Digest 403
December 30, 2022
The Federal Transit Administration’s Enhanced Mobility of Seniors and Individuals with Disabilities program (49 U.S.C. 5310) provides formula funding to help private nonprofit groups meet the transportation needs of older adults and people with disabilities when existing transportation service is unavailable, insufficient, or inappropriate. The TRB National Cooperative Highway Research Program's N...
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NCHRP Research Results Digest 402
January 22, 2018
TRB’s National Cooperative Highway Research Program (NCHRP) Research Results Digest 402: Continuing Project to Synthesize Information on Highway Problems provides a 2018 update on current knowledge and practice, in a compact format, without the detailed directions usually found in handbooks or design manuals. Each report in the series provides a compendium of the best knowledge available on those ...
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NCHRP Research Results Digest 401
January 16, 2017
TRB’s National Cooperative Highway Research Program (NCHRP) Research Results Digest 401: Continuing Project to Synthesize Information on Highway Problems is a digest of the progress and status of NCHRP Project 20-5, “Synthesis of Information Related to Highway Problems.”
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NCHRP Research Results Digest 400
November 21, 2016
TRB's National Cooperative Highway Research Program (NCHRP) Research Results Digest 400: Sample Size Implications of Multi-Day GPS-Enabled Household Travel Surveys summarizes an NCHRP project that studied the design of household travel surveys. Multi-day travel surveys are now more feasible, given global positioning system (GPS) technology. This project explores if surveys using a GPS device provi...
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NCHRP Research Results Digest 399
August 17, 2016
TRB’s National Cooperative Highway Research Program (NCHRP) Research Results Digest 399: Field Validation of Laboratory Tests to Assess Cracking Resistance of Asphalt Mixtures: An Experimental Design develops an experimental design, including a proposed schedule and budget, for the field validation of laboratory tests selected under this study to assess the potential for the four types of cracking...
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NCHRP Research Results Digest 398
January 14, 2016
TRB’s National Cooperative Highway Research Program (NCHRP) Research Results Digest 398: Continuing Project to Synthesize Information on Highway Practices is a digest of the progress and status of NCHRP Project 20-5, “Synthesis of Information Related to Highway Practices.”
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NCHRP RRD 397
December 26, 2015
TRB’s National Cooperative Highway Research Program (NCHRP) Research Results Digest 397: Independent Cost Estimates for Design and Construction of Transit Facilities in Rural and Small Urban Areas explores the distinct characteristics of rural and small urban area transit facilities and historical cost data. The report includes a prototype tool that may assist agencies with preparing conceptual es...
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NCHRP Research Results Digest 396
October 14, 2015
TRB’s National Cooperative Highway Research Program (NCHRP) Research Results Digest 396: Approach to Level-of-Service Target Setting for Highway Assets identifies methodologies and provides guidance for selecting level-of-service targets for maintaining and operating highway assets. In the past, targets have often been established based on the expert opinion of individuals and have not neces...
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NCHRP Research Results Digest 395
June 04, 2015
TRB’s National Cooperative Highway Research Program (NCHRP) Research Results Digest 395: Claims Related to Stormwater Discharge is being revised. It will be reposed on this site as soon as revisions are completed.
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NCHRP Research Results Digest 394
June 20, 2015
TRB’s National Cooperative Highway Research Program (NCHRP) Research Results Digest 394: Estimating the Long-Term Impacts of MAP-21 on the Nation’s Local Rural Transit Bus Infrastructure explores an analysis of the long-term impacts of the Moving Ahead for Progress in the 21st Century Act (MAP-21) on the nation’s rural transit infrastructure. This analysis includes a review of funding levels begin...
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NCHRP Research Results Digest 393
April 08, 2015
TRB’s National Cooperative Highway Research Program (NCHRP) Research Results Digest 393: Selected Indirect Benefits of State Investment in Public Transportation explores the full range of benefits that may be associated with investment in public transportation programs, including those that could help offset the cost of transit investments and operations. Specifically, this report identifies and d...
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NCHRP Research Results Digest 392
January 13, 2015
TRB’s National Cooperative Highway Research Program (NCHRP) Research Results Digest 392: Continuing Project to Synthesize Information on Highway Problems is a digest of the progress and status of NCHRP Project 20-5, “Synthesis of Information Related to Highway Problems.”
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February 04, 2015
TRB’s National Cooperative Highway Research Program (NCHRP) Research Results Digest 391: Modulus-Based Construction Specification for Compaction of Earthwork and Unbound Aggregate develops a modulus-based construction specification for acceptance of compacted geomaterials.
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NCHRP Research Results Digest 390
November 23, 2014
TRB’s National Cooperative Highway Research Program (NCHRP) Research Results Digest 390: Precision Estimates of AASHTO T 324, “Hamburg Wheel-Track Testing of Compacted Hot Mix Asphalt (HMA)” presents new precision statements for the Hamburg wheel tracking test, which is a test used to identify mixtures prone to rutting or moisture damage.
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NCHRP Research Results Digest 389
June 05, 2014
TRB’s National Cooperative Highway Research Program (NCHRP) Research Results Digest 389: Precision Estimates of AASHTO T 304, AASHTO T 96, and AASHTO T 11 and Investigation of the Effect of Manual and Mechanical Methods of Washing on Sieve Analysis of Aggregates updates precision estimates of American Association of State Highway and Transportation Officials (AASHTO) T 96, T 304, and T 11. The rep...
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NCHRP Research Results Digest 388
May 07, 2014
TRB’s National Cooperative Highway Research Program (NCHRP) Research Results Digest 388: Precision Estimates of AASHTO T 201, AASHTO T 202, and AASHTO T 49 presents new, updated precision statements for three asphalt binder test methods. The new methods are based on the analysis of 168 proficiency data sets.
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NCHRP Research Results Digest 387
July 21, 2014
TRB’s National Cooperative Highway Research Program (NCHRP) Research Results Digest 387: Alternative Delivery Methods for Winter Maintenance Operations develops a decision-making framework to guide public road agencies’ delivery of winter maintenance operations.
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NCHRP Research Results Digest 386
January 03, 2014
TRB’s National Cooperative Highway Research Program (NCHRP) Research Results Digest 386: Continuing Project to Synthesize Information on Highway Problems is a digest of the progress and status of NCHRP Project 20-5, “Synthesis of Information Related to Highway Problems.”
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NCHRP RRD 385
December 30, 2013
TRB’s National Cooperative Highway Research Program (NCHRP) Research Results Digest 385: The Legal Definitions of “First Responder” explores the definition of “first responders.” The report also contains an analysis of grants available from the federal government to aid state and local governmental entities in preparing for and responding to natural or man-made disasters and emergencies.
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NCHRP RRD 384
December 21, 2013
TRB’s National Cooperative Highway Research Program (NCHRP) RRD 384: New Urban Areas: A Transit Guidance Brief addresses issues that are likely to be encountered in starting transit service or implementing urban transit service.
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