Traffic Access and Impact Study Guidelines & Procedures

Back to Special Planning Regulations
Printer Friendly View

These traffic access and impact study requirements define when proposed comprehensive plan amendment, zone change, subdivision plans and development plans warrant a detailed traffic access and impact study and the type of information that should be included in such a study. All applicants will be required to follow Planning Commission requirements and will be treated equally under the same or similar circumstances.

 I.          Purpose

The purpose of performing a traffic access and impact study, as defined by the Institute of

Transportation Engineers (ITE), is to: 

1. Provide guidance for short- and long-range planning of site access;
2. Provide guidance for on-site circulation and the interface between on-site circulation and off-site traffic;
3. Provide guidance for off-site improvements needed to permit the roadway system to function satisfactorily so as to accommodate site and non-site traffic;
4. Assist developers and land owners in making land use site planning decisions regarding traffic;
5. Identify the contribution a particular development makes to roadway system traffic volumes;
6. Provide a basis for estimating roadway improvement requirements attributable to a particular project;
7. Assess the compatibility with local transportation plans (Transportation Element of the Comprehensive Plan);
8. Enable staff to better evaluate zoning changes and development plans; and
9. Allow appointed and elected officials to know implications of their voting decisions.

II.        Qualifications

The traffic access and impact study shall be prepared by or under the direct supervision of a Technically qualified transportation engineer with training and experience in conducting Traffic access and impact studies. The professional in charge shall be an actively licensed Professional Engineer in Kentucky. The Engineer’s seal and signature shall be placed on the cover page. The submitted report also shall include in an appendix the qualifications of the responsible professional plus those of any other transportation professionals taking part in the study.

III.       When a Study is Required

A traffic access and impact study shall be required when the total estimated average peak hour trip ends equals 100 or more. Where locally-derived trip generation data do not exist, the current edition of the Institute of Transportation Engineers Trip Generation¹ may be used to estimate the number of peak hour trip ends for a proposed development. “Peak hour” is defined as the peak sixty-minute period that occurs during a typical weekday morning, mid-day or afternoon/evening or on a Saturday.

IV.       Pre-Application Meeting

Prior to initiation of the traffic study, a pre-application meeting shall be held between the Applicant and Georgetown-Scott County Planning Commission (GSCPC) staff.  Other invited parties may include the Kentucky Department of Highways (District 7 and/or Central Office), City of Georgetown and/or Scott County Fiscal Court. Topics to be discussed could include:

• Definition of the proposed project
• Study area/transportation facilities to be included in the analyses
• Horizon year(s)/analysis scenarios
  
  °   Opening date
  °   Anticipated buildout or full development
  °   Interim years or phases
   

• External factors that could affect the proposed development
  
  °   Planned roadway improvements
  °   Other developments nearby
   

• Analysis periods
  
  °   Weekday A.M. peak
  °   Weekday Mid-day peak
  °   Weekday P.M. peak
  °   Saturday peak
  °   Other peak period(s) as necessary (e.g., Toyota Motor Manufacturing of Kentucky shift change,
      special events, etc.)
   

• Traffic data
  
  °   Data to be collected
  °   Available data from other sources
   

• Trip generation
  
  °   Source(s)
  °   Pass-by and diverted traffic rate assumptions
   

• Methodology for background (non-project) estimates and forecasts
  
  °   Current traffic volumes
  °   Forecasts
   

• Methodology for site traffic assignments
  
  °   Directional distribution for approach and departure traffic
  °   Site traffic distribution
   

• Analytical tools
  
  °   Highway Capacity Manual/Highway Capacity Software
  °   Other deterministic models
  °   Simulation
   

• Required performance measures
• Additional analyses needed
  
  °   Signal warrant analyses
  °   Safety studies
   

• Documentation

V.        Analysis Periods

Operational analyses shall be conducted for peak sixty-minute periods:

• For a typical weekday A.M. peak
• For a typical weekday mid-day peak
• For a typical weekday P.M. peak

The GSCPC staff may require an additional analyses for a typical Saturday peak hour depending on the type of development (retail, for example) and location. Additionally, the GSCPC staff may waive the need for an analysis of the mid-day peak based on the type of development being proposed and location.

VI.       Analysis Scenarios

Analyses shall be performed for the required peak periods for the following scenarios:

• Existing or base year
• Opening year of the proposed project, without the estimated site traffic (“No Build”)
• Opening year of the proposed project, including the estimated site traffic
• Buildout or completion year of the project if the project will be constructed in multiple phases; completion year, shall be analyzed with and without mitigation measures (see section XIII)

VII.     Study Area

Each traffic access and impact study is different, both in the type of development being proposed and in its location within Scott County. Thus, the study area and transportation network to be analyzed will be determined jointly by the applicant and GSCPC staff and will include all major arterials and minor collectors that provide access to the proposed development site. It also may determine that specific minor arterial and collector streets should be included in the analyses as well. The study area network is to include all proposed access points to the project within the adjacent roadway network and major intersections, both signalized and unsignalized.

 VIII.    Trip Generation

Estimation of site-generated traffic volumes or trip ends should be performed using a source or sources approved by the GSCPC. Trip generation volumes are most commonly computed from data contained in the latest edition of the ITE Trip Generation manual. In the event that data for the proposed land use are not available in Trip Generation or are not appropriate for the proposed land use, data from similar developments should be collected and trip generation rates from these data be developed accordingly. Guidelines for collecting trip generation data and developing trip generation rates are presented in the ITE Trip Generation Handbook².  Traffic generation estimates from data presented in the Trip Generation manual can be made using one of three sources for each combination of land use type, independent variable (i.e. development size) and time period: 

• Data plot
• Weighted average trip generation rate
• Regression equation

Guidance for proper use of these sources is presented in the Trip Generation Handbook and should be followed in performing traffic access and impact studies.

Traffic estimates using weighted average trip generation rates or regression equations from Trip Generation represent an average number of trips for a given land use type and independent variable (square feet, for example). After these trip estimates are made, they should be increased by ten (10) percent in order to represent a typical “busy” day for the proposed development.

Multi-use developments afford the opportunity for interaction among land uses within an individual site and thus a reduction in total trips to and from the site. An internal capture rate can be applied as a percent reduction to trip generation estimates to account for trips internal to the site. Trip reduction for internal trips is separate from a reduction for pass-by trips. If applicable, internal capture trips should be subtracted before pass-by trip reductions are applied. Guidance on the estimation of internal capture rate is contained in the Trip Generation Handbook.

IX.       Trip Distribution and Assignment

Directional distribution of approach and departure site traffic may be performed in one of the following ways:

• In proportion to existing or projected traffic volumes on adjacent streets and roads
• Using the Scott County Travel Demand Model (with assistance from the GSCPC)
• Applying a manual gravity model
• By other means (justification must be provided)
• Guidance for assignment of project traffic to site access points is provided in Transportation and Land Development³.

X.        Analytical Tools

Allowable analytical tools can be grouped into two general categories: macroscopic and microscopic. Any macroscopic tool used must implement the most recent version of the Highway Capacity Manual⁴ (HCM). Several software packages attempt to faithfully replicate methods in the HCM and are acceptable for use in traffic access and impact studies. However, non-HCM methods such as the Intersection Capacity Utilization (ICU) and percentile delay-based level of service (LOS) shall not be used if contained in a software package.

HCM methods have limitations and in some cases, microscopic simulation models will be more appropriate. Situations where HCM methods are limited and therefore simulation would be more appropriate include high degrees of oversaturation (i.e., where demand exceeds capacity), turn lane overflow, demand starvation (congestion and/or back-ups prohibit turning vehicles from reaching turn lanes), and closely spaced traffic signals on an urban street.

In the event that a proposed roundabout is being evaluated, either the HCM method, microsimulation, or software specifically written for roundabout analyses, may be used.

XI.       Performance Measures

Performance measures, qualitative and quantitative, relay information on the performance of the transportation system. Performance measures should be appropriate for those facility types being analyzed. The following performance measures, by facility type, should be included in traffic access and impact studies:

Unsignalized Intersections

• Control delay
• LOS (HCM only)
• Volume-to-capacity ratio (v/c) (HCM only)
• 95th-percentile queue

These measures shall be reported for those lanes/lane groups required to yield to through movements (i.e. minor street approaches, left turns on major street approaches). A weighted average delay for the entire intersection, if computed using simulation software, shall not be reported for unsignalized intersections.

Signalized Intersections

• Control delay
• Level of service (HCM only)
• Volume-to-capacity ratio (v/c) (HCM only)
• 95th-percentile queue

These measures shall be reported for individual lane groups and approaches.

Urban Streets

• Average travel speed
• Number of stops (simulation only)
• Level of service (by segment and overall) (HCM only)

Roundabouts

• Control delay
• Level of service (HCM only)
• Volume-to-capacity ratio (v/c) (HCM only)
• 95th-percentile queue

These measures shall be reported for individual lane groups and approaches.

Two-Lane Highways

• Volume-to-capacity ratio (v/c) (HCM only)
• Level of service (HCM only)

Multi-lane Highways

• Average speed
• Density
• Level of service (HCM only)

XII. Other Analyses

In addition to operational analyses, other analyses of the transportation system and impacts by the proposed development may be required. These include:

Signal Warrant Analysis

A supporting signal warrant analysis shall be performed if a new traffic signal is being assumed and/or recommended as part of the proposed development. The warrant analysis shall be performed in accordance with guidelines presented in the Manual on Uniform Traffic Control Devices⁵ (MUTCD). Off-peak traffic volumes can be estimated or projected for the purpose of comparison with warrant criteria. Justification for off-peak traffic estimates must be provided.

Safety Analysis

When determined necessary by the GSCPC staff, a safety analysis shall be conducted for those streets and roads where site access is being proposed. The analysis shall include an assessment of existing roadway conditions for the following elements: horizontal and vertical geometry, sight distance, pavement condition, shoulder width/clear zone width, traffic control, and pedestrian/bicycle facilities. Crash data (if available) for the last three (3) to five (5) years should be examined. Crash frequencies and rates should be tabulated and compared to statewide averages using the most current version of Analysis of Crash Data in Kentucky⁶. Crash types/causative factors should be tabulated and, where determined necessary by the GSCPC staff, collision diagrams shall be prepared.  For those locations where speed is determined to be a significant causative factor, analyses and recommendations shall include speed mitigation measures.

The crash analysis shall include a discussion of recommended roadway enhancements to improve safety in the vicinity of the proposed access to the project site and their anticipated effectiveness.

Assessment of Transit/Bicycle/Pedestrian Facilities

When deemed desirable by the GSCPC staff, an assessment of existing transit, bicycle and pedestrian facilities within the project impact area shall be performed by the applicant. The assessment shall include identification of current transit, bicycle and pedestrian facilities – description, location, and current condition or state of use. Transit facilities shall include bus stops, especially school bus stops. Pedestrian facilities shall include sidewalks, crosswalks and pedestrian signals at intersections. The assessment also should include an evaluation of how the proposed development will impact these current facilities and recommendations for improvements.

XIII.    Mitigation

The study should identify current and/or future anticipated deficiencies in the impact area roadway system, particularly those deficiencies that would occur as a result of the proposed development being built. The study should include feasible recommendations to mitigate development impacts and the anticipated effectiveness of those recommendations, both operationally and with respect to safety. Cost estimates (to include engineering, construction and right-of-way) should be provided. The study should also include an assessment of traffic conditions with construction of the proposed development but without the recommended mitigation improvements.

XIV.    Documentation/Supporting Information

The applicant shall submit a final report documenting the study process, the analyses and the results. The report shall be submitted in both hard copy and electronic (PDF) format. The desired number of hard copies will be determined by the GSCPC staff. The report shall include the following elements:

• Executive summary
• Development summary
• Location map
• Study area boundaries and roadway network
• Study area intersection photographs, existing roadway cross-sections, project access points(s), etc.
• Assessment of existing traffic conditions
• Traffic growth and future No Build traffic conditions
• Summary of proposed development
• Trip generation
• Trip distribution, mode split (where applicable), and assignment
• Assessment of future traffic conditions
• Conclusions and recommendations
• Appendices
  • HCS/other software output
  • Signal warrant analyses
  • Preparer’s qualifications
  • Other pertinent information

__________________

1 Trip Generation, 7th Edition, Institute of Transportation Engineers, Washington, D.C., 2003 (current edition).
2 Trip Generation Handbook: An ITE Recommended Practice, Institute of Transportation Engineers, Washington,
   D.C., March 2001.
3 Stover, Vergil G. and Frank J. Koepke, Transportation and Land Development, 2nd Edition, Institute of
   Transportation Engineers, Washington, D.C., 2002.
4 Highway Capacity Manual, Transportation Research Board, National Academy of Sciences, Washington,
   D.C.
5 Manual on Uniform Traffic Control Devices, United States Department of Transportation, Federal
   Highway Administration, Washington, D.C., 2003.
6 Analysis of Crash Data in Kentucky, Research Report KTC-07-26/KSP2-07-1F, Kentucky Transportation
   Center, College of Engineering, University of Kentucky, Lexington, Kentucky, 2007.