[HISTORY: Adopted by the City Council of the City of Harrisburg
by Ord. No. 23-1990. Amendments noted where applicable.]
CROSS-REFERENCES
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.
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.
B.
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:
(1)
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
(2)
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.
C.
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.
D.
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.
E.
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.
F.
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.
G.
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.
H.
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.
I.
Any significant difference between the sums of single-use rates and
proposed mixed-use estimates must be justified and explained in the
report.
J.
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.
B.
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.
A.
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.
B.
If a thorough analysis is required to account for pass-by trips,
the following procedure should be used:
C.
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.
A.
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.
B.
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.
C.
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.
D.
Several other factors should also be analyzed. These include:
(1)
Safety;
(2)
Circulation patterns;
(3)
Traffic control needs;
(4)
Transit needs or impacts;
(5)
Transportation system management;
(6)
Neighborhood impacts;
(7)
Adequacy of on-site parking facilities and/or off-site parking
facilities, if any are to be used for site-generated parking;
(8)
Pedestrian and bicycle movements; and
(9)
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.
A traffic access impact study report shall be prepared to document
the purpose, procedures, findings, conclusions, and recommendations
of the study.
B.
The documentation for a traffic access and impact study shall include,
at a minimum:
(1)
Study purpose and objectives.
(2)
Description of the site and study area.
(3)
Existing conditions in the area of the development.
(4)
Anticipated nearby development.
(5)
Trip generation, trip distribution and modal split.
(6)
Projected future traffic volumes.
(7)
Assessment of the change in roadway operating conditions resulting
from the development traffic.
(8)
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.
A.
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.
B.
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.
C.
Data shall be presented in tables, graphs, maps, and diagrams wherever
possible for clarity and ease of review.
D.
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.
E.
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.
A.
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.
B.
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.
