Managing Roadway Access Using Crash Data and Geographic Information Systems

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Managing Roadway Access Using Crash Data and
Geographic Information Systems
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Presentation Outline

• What is access management?
• Benefits of properly managing access
• Types of crashes associated with access
  management problems
• Techniques and treatments for managing access, a
  brief overview
• GIS as a tool for identifying existing access
  management problems
• Ames, Iowa USA example and results

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What Is Access Management?

• Access Management is the process that provides
  access to land development while simultaneously
  preserving the flow of traffic on the surrounding
  road system in terms of safety, capacity, and
  speed.
• (Source Federal Highway Administration,
• United States Department of Transportation)

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What Is Access Management?

• Where land use planning, real estate development,
  transportation planning, and traffic engineering
  intersect

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Functional IntegrityA Key Access Management
Concept

• Reserve high speed, high capacity roads for high
  speed, long-distance travel
• Maintain a clear hierarchy of roads by function
• Balance traffic movement and access to adjacent
  land by providing direct land access compatible
  with the roadway classification

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Functional Integrity Issues
Typical problem arterials that provide too much
direct access to property and fail to serve
through traffic efficiently
Freeways
Arterials
Through Traffic Movement
Collectors
Locals
Locals that serve excessive through traffic lead
to demand for traffic calming
Access to Property
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What Are The Benefits Managing Access?

• Improved safety
• Reduction in crashes and crash rates
• Improved traffic operations
• Increased traffic level of service, capacity, and
  travel speed
• Safety and operational benefits for pedestrians,
  bicyclists, and public transit buses
• Lower overall costs for taxpayers
• Improved air quality

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Conflict Points at Public Road Intersections and
Private DrivewaysA Major Concern of Access
Management
All conflict points represent potential crash
locations
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Statistical Relationship Between Access Density
and Crash Rates
The relationship between commercial driveway dens
ity and crashes is very evident and strong.
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Statistical Relationship Between Access Density
and Crash Rates
However, residential driveway density does not
appear to represent a safety concern.
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There is a strong correlation between access
density and broadside collisions
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There is a strong correlation between access
density and rear-end collisions

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Safety Benefits Iowa Case Studies

• Seven Iowa case studies were studied on a before
  and after basis
• Case studies show nearly a 40 percent average
  reduction in accident rates after projects
  incorporating access management treatments were
  completed

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Safety BenefitsCrash Reduction By Type For Iowa
Case Studies
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Common Access Management Treatments

• Driveway consolidation
• Corner clearance
• Alternative access ways
• Includes internal site design, frontage roads,
  and backage roads
• Continuous two-way left-turn lanes (TWLTL)
• Medians at intersections
• Full raised medians

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Driveway Consolidation and Corner Clearance
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Alternative Access Ways Backage Road
Commercial Property
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Two-Way Left Turn Lane (TWLTL)
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Strategic Process for Analyzing Existing Access
Management Problem Corridors Goals

• Get the big picture view of an entire
  metropolitan area or city in terms of access
  management
• Be able to zoom in on specific corridors that
  appear to have poor and good access management
  characteristics
• Produce results that are visual, to aid in the
  education of citizens, business owners, and
  elected decision-makers

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Strategic Process for Analyzing Existing Access
Management Problem Corridors Methodology

• Used a geographic information system (GIS) as a
  platform to integrate relevant data from a number
  of sources
• GIS platform--ESRI ArcView 3.1
• Integrated a variety of spatial data from several
  sources
• Identified a number of specific corridors that
  have poor and good access management
  characteristics
• Compared resultant list of corridors needing
  attention with other indicators, including
  citizen survey results

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Strategic Process Main Spatial Data Sources

• Roadways line work database
• Iowa Department of Transportation
• Current and forecast traffic volumes (AADT)
• Iowa Department of Transportation
• Historic crash database (up to 10 years of data)
• Iowa Department of Transportation (GIS-ALAS)
• Commercial land use from remote sensing
• Iowa Department of Natural Resources
• Digital orthophotography
• Story County

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Some Results

• Overall map of access management problem areas
  for
• City of Ames, Iowa USA
• Population 50,000
• Zoom in to Southeast quadrant of city
• Shows concentrations of problem areas
• Example of a well-managed corridor
• South Duff Avenue
• Example of a poorly-managed corridor
• Lincoln Way

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Full Raised Median
Big picture view of Ames
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Full Raised Median
Southeast quadrant of Ames showing two corridors
needing better access management
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Full Raised Median
Example of good access management few
access-related crashes
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S. Duff Avenue Near S. 16th Street (US Highway 69)

• Low commercial driveway
• density due to access treatments
• Extensive system of frontage
• and backage roads
• Turning lanes throughout
• TWLTL and some medians
• recently added

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Full Raised Median
Examples of poor access management numerous
crashes characteristic of poor access management
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Lincoln Way Between N. Grand and S. Duff (US
Highway 69)

• High commercial driveway
• density
• Poor corner clearance
• No turning lanes
• No median or TWLTL

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Statistical Comparison Between The Two Examples
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Comparison With Other Problem Identification
Methods

• Lincoln Way was the number one problem arterial
  roadway identified in its latest survey of
  citizens
• Rated very poor (the lowest rating possible) by
  27 percent of the survey respondents
• The well-managed portion of South Duff received
  no votes from citizens as a problem arterial
  route
• This section of roadway was recently improved
  using a TWLTL and driveway treatments
• The crash rate declined by 70 percent

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Conclusions

• Access management is an extremely effective and
  beneficial transportation management tool
• GIS can allow integration of multiple data
  sources needed to identify access management
  problem locations on a big picture and
  corridor-specific basis
• GIS results are highly visual and correlate very
  well with results from other problem
  identification methods

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For More Information, Contact
David J. Plazak Associate Director for
Policy Center for Transportation Research and
Education Iowa State University Research
Park 2901 South Loop Drive, Suite 3100 Ames, IA
50010-8632 USA 1-515-294-8103 (Phone) 1-515-294-04
67 (Fax) dplazak_at_iastate.edu http//www.ctre.iast
ate.edu/database/access_management.html