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Designing for Target Speed

Description:

The current state of practice for designing roadways within the United States is to choose a “design speed” for a roadway and use that speed as an input to determine other roadway factors. AASHTO defines design speed as follows:

_Design speed is a selected speed used to determine the various geometric features of the roadway. The assumed design speed should be a logical one with respect to the topography, anticipated operating speed, the adjacent land use, and the functional classification of the highway. _

The definition for “target speed” is the speed that you intend for drivers to go, rather than “design speed”. For example, a straight roadway with 12-foot travel lanes and no curbs in an urban setting may technically have a “design speed” of 45 mph due to its design characteristics, but the desired “target speed” for that roadway may be 25 mph.

The topic of “design speed” versus “target speed” typically centers on roadways with speed limits between 25 mph and 45 mph especially where the 85th percentile speed is higher than the posted speed limit. Agencies are often asked the question “What can be done to reduce the speeds to obtain a desired target speed?” and that question is often difficult to answer due to the nature of design with speed being an input instead of an output along with knowing what roadway and non-roadway elements actually influence a driver’s speed choice.

The purpose of this research is to investigate the question of what roadway / non-roadway elements influence operating speed. This research would focus on roadways with a posted speed limit between 30 and 40 mph, typically collectors and arterials within an urban/suburban context. The research would review various elements of roadways where the 85th percentile speed is at or near the posted speed (within 5 mph) and those roadways where the 85th percentile speed is over the posted speed limit by 10 mph or more. These elements could include roadway width, shoulder width, presence of curbs, driveway density, tree density and size, presence of on-street parking, presence of on-street bicycle facilities, presence of transit stops, roadway curvature (both horizontal and vertical), signal density, presence of sidewalks, sidewalk width and setback, building setback, land use, pedestrian and bicyclist activity, as well as others. The result of the research should provide the profession with better knowledge of what elements may affect speed and how to incorporate those elements into better design.

Objective:

The objectives of this research are as follows:

· Summarize the research conducted in this area, including identifying how those findings should be considered when collecting data in Phase II of the project.

· Identify elements that influence speed, including roadway and non-roadway features. Examples of roadway features include lane width, shoulder width, etc. Examples of non-roadway features include the presence of trees, building setback, land use, etc.

· Identify and evaluate two different sets of roadways with posted speeds between 30 and 40 mph that have:

o 85th Percentile Speed that is within 5 mph of Posted Speed.

o 85th Percentile Speed that is over 10 mph of Posted Speed.

· Determine how the identified roadway and non-roadway elements influence operating speed and/or influence the speed difference between the 85th percentile speed and the posted speed limit.

· Recommend best practice for which roadway and non-roadway elements should be considered when an agency selects a target speed. Develop recommendations on how the findings can be incorporated into the design process.

Benefits:

Given the recent push by local/county jurisdictions to identify characteristics to reduce speeds and implement the use of “target speed” instead of “design speed”, the urgency is between one to three years. The potential values to state DOTs is to address the gap that exists on how various roadway and non-roadway elements influence speed and incorporate that knowledge into the design process. The likelihood that this research can be achieved within the given timeframe is high, given state/local participation in the research. The likelihood that this research would be used by state DOTs is high, as well as local/county agencies. This research topic was listed as a high priority by the AASHTO Technical Committee on Geometric Design during their June 2018 joint meeting with the TRB Committee on Geometric Design and the TRB Committee on Operational Effects of Geometrics.

Related Research:

· Bassan, Shy, “Highway Design Policy Insights for Target Speed: an Israel Perspective”, Traffic Engineering & Control, Volume 57, Issue 4, 2016, pp 155-158.

· “Traffic Safety Advocates Target Speed”, Traffic Safety (Chicago), Volume 04, Issue 5, 2004, p. 2.

· Braaksma, JP, “Target Speeds for Speed Zoning and Traffic Calming in Residential Areas”, 2001 Annual Conference and Exhibition of the Transportation Association of Canada, September 16-19, 2001, Halifax, Nova Scotia: Partnering For Success In Transportation, 2001.

· Jiang, Zhouton, et al, “Speed Harmonization—Design Speed vs. Operating Speed”, Civil Engineering Studies, Illinois Center for Transportation Series, Issue 16-021, 2016, 92p.

· Deller, J, “The influence of road design speed, posted speed limits and lane widths on speed selection: methodology for simulator and observational research study”, Australian Institute of Traffic Planning and Management (AITPM) National Conference, 2015, Brisbane, Queensland, Australia, 2015, 12p.

· Lazda, Z, et al, Smirnovs, “Application of Design Speed for Urban Road and Street Network”, Baltic Journal of Road and Bridge Engineering, Volume 9, Issue 1, 2014, pp 26-30.

· Deller, J, “The influence of road design speed, posted speed limits and lane widths on speed selection: a literature synthesis”, Australasian Transport Research Forum (ATRF), 36th, 2013, Brisbane, Queensland, Australia, 2013, 14p.

· Choi, Jaisung, et al, Effects of Changing Highway Design Speed, Journal of Advanced Transportation, Volume 47, Issue 2, 2013, pp 239-246.

· Porter, Richard J, et al, Geometric Design, Speed, and Safety, Transportation Research Record: Journal of the Transportation Research Board, Issue 2309, 2012, pp 39–47.

· Faghri, A, et al, Design Speed Selection Recommendations, University of Delaware, Newark, Delaware Department of Transportation, 2004, 92p.

· Harwood, Doug, Alternatives to Design Speed for Selection of Roadway Design Criteria, National Cooperative Highway Research Program, Project 15-25, 2008.

· Stamatiadis, Nikiforos, Analysis of Inconsistencies Related to Design Speed, Operating Speed and Speed Limits, Kentucky Transportation Center Research Report, 2004, 64p

· Fitzpatrick, Kay, et al, Design Speed, Operating Speed, and Posted Speed Practices, NCHRP Report, Issue 504, 2003, 101 p.

· Recent and in-process research, including:

o NCHRP Report 737: Design Guidance for High-Speed to Low-Speed Transitions Zones for Rural Highways

o NCHRP Report 839: A Performance-Based Highway Geometric Design Process

o NCHRP Project 15-48 (Report 880): Guidelines for Designing Low and Intermediate Speed Roadway that Serves All Users

o NCHRP Project 17-58: Safety Prediction for Urban and Suburban Arterials. Report available at: https://ceprofs.civil.tamu.edu/dlord/Papers/FinalReportNCHRP17-58withAppendicesJune_2016.pdf

o Ongoing NCHRP Project 17-76: Influences on Operating Speed

· US Department of Transportation Publications

o Speed Management Toolkit, Federal Highway Administration (FHWA)

o Speed Management Program Plan, National Highway Traffic Safety Administration (NHTSA)

o Reducing Speeding-Related Crashes Involving Passenger Cars, National Transportation Safety Board (NTSB)

o Highway Design Handbook for Older Drivers and Pedestrians, FHWA-RD-01-103

· Other Documents for Consideration

o Designing Walkable Urban Thoroughfares: A Context Sensitive Approach, Institute of Transportation Engineers (ITE)

o Project Development and Design Guide, Massachusetts Department of Transportation

o Highway Design Manual, Washington State Department of Transportation

o Speed Zoning Manual and Florida Design Manual, Florida Department of Transportation

o Towards Safe System Infrastructure: A Compendium of Current Knowledge, Austroads Publications Online

o Safe System Approach in Australia and New Zealand

Tasks:

The duration is based on spending approximately the first 6 months conducting a literature search and summary of previous research, as well as the determination of roadway and non-roadway elements to include in the research. The next 6 months would identify roadways to evaluate, which would involve working with state DOTs and local jurisdictions to determine availability of data. The next twelve months would involve collecting and evaluating the speed and roadway / non-roadway data. Finally, the remaining time would involve evaluating the findings and developing recommendations and documentation.

Implementation:

State DOTs would use this information to determine which roadway/non-roadway elements could be modified in order to reduce speeding. This could involve providing information to local/county roadway agencies, conducting a pilot test on their own roadway, or provide assistance (financial or non-financial) to local/county roadway agencies for a pilot project to evaluate recommendations in the report.

Sponsoring Committee:AKD10, Performance Effects on Geometric Design
Research Period:24 - 36 months
Research Priority:High
RNS Developer:Sarah Binkowski, Jim Rosenow, Hermanus Steyn, Kay Fitzpatrick
Source Info:This problem statement was developed in connection with the June 2018 mid-year joint meeting of the AASHTO Technical Committee on Geometric Design, the TRB Committee on Geometric Design (AFB10), and the TRB Committee on Operational Effects of Geometrics (AHB65).
Date Posted:09/21/2018
Date Modified:12/31/2018
Index Terms:Design speed, Traffic speed, Collector streets, Arterial highways, Highway design,
Cosponsoring Committees: 
Subjects    
Design
Operations and Traffic Management

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