Appendix E: Guidelines for Traffic Impact Reports/Studies

The purpose of a Traffic Impact Study (TIS), prepared for submittal to the Maryland State Highway Administration (SHA), is to review impacts of the proposed development on the State Highway System, generally in conjunction with the issuance of an access permit. The evaluation should consider traffic capacity, signalization and safety issues. This report will be used to determine the needed improvements in the vicinity of the site access and provide data to the State (and local jurisdictions) on what off-site improvements need to be considered.

The following are intended as guidelines for preparing a traffic impact report for developments which will affect the State Highway system. Traffic reports prepared for the counties should include analyses consistent with these guidelines when state roadways are involved. Some counties have guidelines of their own and these are not intended to replace those guidelines, but rather supplement them.

A TIS may be required for any development that generates more than 50 peak hour trips. For any TIS prepared as a requirement of local jurisdiction guidelines, with a lower threshold, SHA would expect the report to conform to these guidelines when State highways are involved.

Once it is determined that an impact study is required, a scoping meeting may be held with the developer or his consultant and the appropriate representatives of the SHA and/or local jurisdiction. It will be the responsibility of the consultant to initiate this meeting, working through SHA's Engineering Access Permit Division (EAPD). The purpose of this meeting is to discuss site specific information concerning the development. All interested parties should receive copies of the minutes from this meeting.

The study area should generally be in accordance with Local Adequate Public Facilities Ordinance (APFO) guidelines which may be modified during the scoping meeting in consultation with SHA. In the absence of local guidelines, the network should be analyzed to the nearest signalized public street intersection in all directions from each access point; generally not greater than one mile from the access point(s).

An Impact Study Report should include the following information:

  1. Table of Contents
  2. Introduction
    • Explanation of Project/Purpose of Report
    • Area Map showing site location
  3. Existing Conditions
    • Traffic counts & analysis
    • Existing Lane Configuration Sketch
  4. Background Conditions, without site
    • Annual Growth in traffic to build year, if appropriate.
    • Traffic generated by other approved developments.
    • Background Analysis (Background Traffic = Existing Traffic + Growth in Existing Traffic + Approved Development)
    • Background analysis with approved/funded highway projects
  5. Projected Conditions, with site
    • Traffic generated by the proposed development (i.e. site generated traffic) at build out, and/or at any significant stage of development.
    • Total Traffic Analysis (Total Traffic = Existing + Growth + Approved Development + Site Generated)
    • Analyze total traffic with improvements
  6. Conclusions/Recommendations
    • Explain results of analysis
    • The consultant/developer shall suggest reasonable improvements to mitigate the site traffic impacts. (The Level-of-Service (LOS) standard that should be achieved at State intersections is "D".)
  7. Appendix
    • All work sheets, traffic counts and pertinent correspondence
The following is a more detailed explanation of the various aspects involved in preparing the report:
  1. Existing traffic
    • Traffic counts are to be performed at each intersection to be analyzed, if current turning movement counts are not available. The most recent traffic volume counts, whether by SHA, consultant or local jurisdiction, may be used for the study.
    • Counts should, as a rule, not be more than 1 year old from when the report is prepared. Counts between 1 and 3 years old may be used if factored to the current year. Counts older than 3 years will not be accepted.
    • Peak hour counts are acceptable at intersections, generally 7-9 AM and 4-6 PM.
    • Counts are not to be taken on State or Federal holidays.
    • The presence of schools in the area must be considered when determining the date of counts.
  2. Analysis
    • All intersections will be analyzed using the SHA critical lane technique and factors as described in the Appendix No. 1 of these guidelines. In certain circumstances other methodologies, including the Highway Capacity Manual (HCM), might be appropriate to identify operational problems.
    • If required, link analyses will be performed using HCM procedures. Link analyses are appropriate in rural areas when there are no signalized intersections or stop signs on the road being analyzed within the study area. For a two lane roadway, SHA will accept a V/C ratio of up to .90 of the LOS "E" capacity.
    • For analysis of freeways and interchanges, including merge, diverge and weaving areas, the HCM will be used.
  3. Trip Generation and Distribution
    • Local trip generation rates should be used. If local rates are not available, the latest ITE Trip Generation Rates should be used. In the event ITE does not address the development, or is of a limited sample size, studies of similar uses may be used. Documentation of these studies should be submitted for verification.
    • There must be some discussion of the assumptions behind the distribution of generated trips (both site and approved development). The methodology to be used should be discussed at the scoping meeting.
  4. Growth in Existing Traffic
    • Growth in existing traffic is described as a factor representative of travel growth outside the study area. This factor should be applied to the existing through traffic, and appropriate turning movements, before approved development traffic is applied. The volume should be compounded to the reasonable build out years, typically 3-10 years, depending on the build out schedule. For developments with a build out of less than 3 years, growth in existing traffic need not be applied. If a local jurisdiction does not require growth in existing traffic, then this factor should not be applied.
  5. Approved Development Traffic
    • Approved development traffic is described as traffic generated by all approved developments within the area at the time of the report preparation. These sites can be obtained from the County and should be documented in the TIS.
  6. Background Analysis
    • Background analysis includes existing traffic, plus growth in existing traffic, plus approved development. This analysis should take into consideration all transportation improvements expected to be in place within the study area. These improvements should include those which are already programmed or bonded by the state, local jurisdiction or developer(s). These improvements should be documented in the TIS.
  7. Projected Conditions
    • Site traffic is described as traffic which will be generated by the development.
    • Total traffic is to be-calculated after the site traffic is projected.
    • After total traffic is developed, an analysis of traffic operations, with projected future roadway improvement in place (i.e. improvements addressed in the background analysis), is to be performed.
    • After the analysis of total traffic is completed, all intersections and/or links within the study area resulting in a Level-of-Service worse than "D" must be identified and improvement(s) recommended.
  8. Conclusions/Recommendations
    • Any improvement suggested as being implemented by "others" should indicate by whom. If funded by a public agency (i.e. the SHA, the Consolidated Transportation Program (CTP) or local jurisdiction equivalent), then a copy of the page from the appropriate document should be included in the report. If funded by another developer, then documentation should likewise be included.
    • There must be some discussion of the feasibility of constructing any recommended improvement. While detailed construction plans are not expected, some discussion of any obvious constraints is necessary.
    • Consideration should be given to providing improvements at locations that experience a significant decrease in capacity due to the proposed development.
    • A final analysis of the study area must be performed to include any recommended improvements.
    • If a traffic signal is to be proposed, then a signal warrant analysis must be performed in accordance with SHA's warrant analysis procedures, found in Appendix No. 2, and included in the report. After review of this analysis, SHA may require additional study, including exploring other alternatives to signalization, before reaching a final determination on the need for a signal.
    • The report should include a discussion of the improvements that the developer will construct and/or fund as part of the, development proposal.
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