Safe-D: Safety through Disruption

Comparison of SHRP2 Naturalistic Driving Data to Geometric Design Speed Characteristics on Freeway Ramps



Current geometric design guidelines provide information to designers on appropriate design speeds for freeway entrance and exit ramps. These guidelines are based on practices developed several decades ago; however, it is not well known how well the speeds suggested by existing design guidance reflect current driving behavior and technologies. The SHRP2 NDS data provides an opportunity to analyze detailed driving data that did not previously exist, to critically review and potentially update existing design guidelines. The proposed project will obtain and analyze detailed data – speed profiles along with selected driver and vehicle variables – from the SHRP2 NDS dataset for portions of trips that occurred on and near freeway ramps. In addition to the SHRP2 data, the research will use information on the design characteristics of the ramps traveled during the SHRP2 study; the road data will be obtained from the RID dataset, plan sheets, and other available sources from the road agencies in the SHRP2 participating states (New York, Indiana, Florida, North Carolina, and Washington). Analysis of the data will compare NDS data and road data to identify relationships between the factors used to select freeway ramp design speed (e.g., radius, superelevation, etc.) and the actual speeds of drivers traveling on those ramps and their associated behaviors (e.g., brake/accelerator use, steering wheel angle, etc.). In addition to the research activities that will be documented through a typical research project report, the findings and conclusions will be reported through a doctoral dissertation. Further anticipated products include recommendations for revisions to the process for determining ramp design speeds in the AASHTO Green Book and related guidance documents, a description of how to conduct a similar study for other roadway features of interest, and suggestions for relevant updates to existing ramp speed prediction tools. Collaboration with a PhD Student from VTTI is anticipated for assistance with the SHRP2 Data Request.

Project Highlights

  • This study compared driving data on freeway ramps from the SHRP2 NDS to design characteristics of those ramps, to develop models for calculating operating speeds at key locations along freeway ramps. The resulting models were further compared to similar models from recent research.
  • Of the variables examined for this study, curve radius, as expected, had one of the greatest effects on ramp operating speed, and the effect was non-linear. As a result, speed increases at a diminishing rate as curve radius increases.
  • The models suggest that drivers’ speed selections are influenced more by where they are going than where they have been. On entrance ramps, the freeway speed limit plays a large role in speed prediction, while the type of traffic control at the crossroad terminal has a larger effect on exit ramps than on entrance ramps.
  • The project describes a data source that could be used in a variety of design and operational studies beyond freeway ramps. The results provide a new way of estimating speed based on many vehicles at many locations, yielding results from a much broader sample of drivers than is found in most previous studies of similar purpose.

Final Report

TTI-01-03 Final Report

EWD & T2 Products

Student Impact Statement -Jayson Stibble (pdf): The student(s) working on this project provided an impact statement describing what the project allowed them to learn/do/practice and how it benefited their education.

Summary Presentation: was created by the researchers to give a description of the project and provide a summary of their findings for use in academic or professional presentations.


Stibbe, J., & Brewer, M.A. (2019, January). Processing SHRP2 Time Series Data to Facilitate Analysis of Relationships Between Speed and Roadway Characteristics. Presented at the 2019 Transportation Research Board Annual Meeting (Published)

Brewer, M.A., & Stibbe, J. (2019, January). Investigation of Design Speed Characteristics on Freeway Ramps Using SHRP2 Naturalistic Driving Data. Presented at the 2019 Transportation Research Board Annual Meeting (Published)

Brewer, M. A., & Stibbe, J. (2019). Investigation of Design Speed Characteristics on Freeway Ramps using SHRP2 Naturalistic Driving Data. Transportation Research Record. (Published) 

Final Dataset

The final datasets for this project are located in the Safe-D Collection on the VTTI Dataverse; DOI:10.15787/VTT1/K11ULD

Research Investigators (PI*)

Marcus Brewer (TTI/TAMU)*
Gene Hawkins (TAMU)

Project Information

Start Date: 2017-04-01
End Date: 2019-04-30
Status: Completed
Grant Number: 69A3551747115
Total Funding: $141,208
Source Organization: Safe-D National UTC
Project Number: TTI-01-03

Safe-D Theme Areas

Big Data Analytics

Safe-D Application Areas

Operations and Design

More Information

UTC Project Information Form

Sponsor Organization

Office of the Assistant Secretary for Research and Technology
University Transportation Centers Program
Department of Transportation
Washington, DC 20590 United States

Performing Organization

Texas A&M University
Texas A&M Transportation Institute
3135 TAMU
College Station, Texas 77843-3135