[HISTORY: Adopted by the City Council of the City of Harrisburg by Ord. No. 23-1990. Amendments noted where applicable.]
Highway Capacity Manual, Transportation Research Board, Washington, D.C., 1985.
Trip Generation, Institute of Transportation Engineers, 4th edition, Washington, D.C., 1988.
Applicants for approval of subdivision or land development plans may be required to submit a traffic impact study, if the same is determined to be necessary by the City Engineer. Based on this study, certain improvements may be identified to provide safe and efficient access to the development or safe and efficient movement of traffic through intersections within the traffic impact study area.
A traffic impact study may be required at the discretion of the City Engineer whenever a proposed development will generate 40 or more additional (new) peak direction (inbound or outbound) trips to or from the site during the development's peak hour. The site's trip generation shall be determined by using the latest edition of the Institute of Transportation Engineers' (ITE) Trip Generation.
In addition, a traffic impact study shall be prepared whenever either one of the following conditions exists within the impact study area as determined by the City Engineer:
Current traffic problems in the local area, such as a high-accident intersection, confusing intersection or an intersection in need of a traffic signal; or
The ability of the adjacent, existing, or planned roadway system to handle increased traffic or the feasibility of improving the roadway system to handle increased traffic.
The traffic impact study area is defined as any intersection within 1/2 mile of an entrance to a proposed development generating up to 40 peak hour trips.
Traffic impact studies shall be prepared under the supervision of qualified, experienced, and registered transportation engineers with specific training in traffic and transportation engineering and at least two years of experience related to preparing traffic studies for existing or proposed developments.
The traffic forecasts shall be prepared for the anticipated opening year of the development, assuming full buildout and occupancy. This year shall be referred to as the "horizon year" in the remainder of this chapter.
Estimates of non-site traffic shall be made and will consist of through traffic and traffic generated by all other developments within the study area. Non-site traffic may be estimated using any one of the following three methods: buildup technique, area transportation plan data or modeled volumes, and trends or growth rates.
The traffic impact study report shall include a table showing the categories and quantities of land uses, with the corresponding trip generation rates or equations, with justification for selection of one or the other, and resulting number of trips. The trip generation rates used must be either from the latest edition of Trip Generation by ITE or from a local study of corresponding land uses and quantities. All sources must be referenced in the study.
If pass-by trips are a major consideration for the land use in question, studies and interviews at similar land uses must be conducted or referenced.
Any significant difference between the sums of single-use rates and proposed mixed-use estimates must be justified and explained in the report.
The reasoning and data used in developing a trip generation rate for special/unusual generators must be justified and explained in the report.
Prior to trip distribution of site-generated trips, an influence area must be defined which contains 80% or more of the trip end that will be attracted to the development. A market study can be used to establish the limits of an influence area, if available. If no market study is available, an influence area should be estimated based on a reasonable documented estimate. The influence area can also be based on a reasonable maximum convenient travel time to the site or delineating area boundaries based on locations of competing developments.
Whichever method is used, trip distribution must be estimated and analyzed for the horizon year. A multi-use development may require more than one distribution and coinciding assignment for each phase (for example, residential and retail phases on the same site). Consideration must also be given to whether inbound and outbound trips will have similar distributions.
Assignments must be made considering logical routings, available roadway capacities, left turns at critical intersections, and projected (and perceived) minimum travel times. In addition, multiple paths should often be assigned between origins and destinations to achieve realistic estimates rather than assigning all of the trips to the route with the shortest travel time. The assignments must be carried through the external site access points and in large projects (those producing 500 or more additional peak direction trips to or from the site during the development's peak hour) through the internal roadways. When the site has more than one access driveway, logical routing and possibly multiple paths should be used to obtain realistic driveway volumes. The assignment should reflect conditions at the time of the analysis. Assignments can be accomplished either manually or with applicable computer models.
If a thorough analysis is required to account for pass-by trips, the following procedure should be used:
Upon completion of the initial site traffic assignment, the results should be reviewed to see if the volumes appear logical given characteristics of the road system and trip distribution. Adjustments should be made if the initial results do not appear to be logical or reasonable.
Traffic estimates for any site with current traffic activity must reflect not only new traffic associated with the site's redevelopment but also the trips subtracted from the traffic stream because of the removal of a land use. The traffic impact report should clearly depict the total traffic estimate and its components.
Capacity analysis must be performed at each of the major street and project site access intersection locations (signalized and unsignalized) within the study area. In addition, analysis must be completed for roadway segments deemed sensitive to site traffic within the study area. These may include such segments as weaving sections, ramps, internal site roadways, parking facility access points and reservoirs for vehicles queuing off site and on site. Other locations may be deemed appropriate depending on the situation.
The recommended level-of-service analysis procedures detailed in the most recent edition of the Highway Capacity Manual must be followed. The City Engineer considers the overall level-of-service ratings A, B, C and D to be acceptable for signalized intersections (level C or better is considered desirable); level-of-service E or F is considered to be unacceptable.
The operational analysis in the Highway Capacity Manual should be used for analyzing existing conditions, traffic impacts, access requirements or other future conditions for which traffic, geometric, and control parameters can be established.
Several other factors should also be analyzed. These include:
Traffic control needs;
Transit needs or impacts;
Transportation system management;
Adequacy of on-site parking facilities and/or off-site parking facilities, if any are to be used for site-generated parking;
Pedestrian and bicycle movements; and
Service and delivery vehicle access.
The recommendations of the traffic impact study shall provide safe and efficient movement of traffic to and from and within and past the proposed development, while minimizing the impact to non-site trips. The current levels of service must be maintained if they are C or D, not allowed to deteriorate to worse then C if they are currently A or B, and improved to D if they are E or F.
A traffic access impact study report shall be prepared to document the purpose, procedures, findings, conclusions, and recommendations of the study.
The documentation for a traffic access and impact study shall include, at a minimum:
Study purpose and objectives.
Description of the site and study area.
Existing conditions in the area of the development.
Anticipated nearby development.
Trip generation, trip distribution and modal split.
Projected future traffic volumes.
Assessment of the change in roadway operating conditions resulting from the development traffic.
Recommendations for site access and transportation improvements needed to maintain traffic flow to, from, within, and past the site at an acceptable and safe level of service.
The analysis shall be presented in a straightforward and logical sequence. It shall lead the reader step by step through the various stages of the process and resulting conclusions and recommendations.
The recommendations shall specify the time period within which the improvements should be made (particularly if the improvements are associated with various phases of the development construction), the estimated cost of the improvements, and any monitoring of operating conditions and improvements that may be required.
Data shall be presented in tables, graphs, maps, and diagrams wherever possible for clarity and ease of review.
To facilitate examination by the City Engineer and the Planning Commission, an executive summary of one or two pages shall be provided, concisely summarizing the purpose, conclusions, and recommendations.
The report documentation outlined above provides a framework for site traffic access/impact study reports. Some studies will be easily documented using this outline. However, the specific issues to be addressed, local study requirements, and the study results may warrant additional sections.
The applicant shall be responsible for improvements required for adequate and safe access to the development site, as well as necessary roadways, walkways, parking facilities, etc., within the site.
The developer's share of off-site improvements within the traffic impact area shall be based on the recommendations of the City Engineer and the City Planning Commission, as determined by City Council.
Payment for the applicant's share of off-site improvements shall be made to the City. An improvement construction guarantee, in conformance with Chapter 7-515, will be required before the final plan is certified by the City Engineer.