Division 13-05-002
Impact Analyses
Sections:
13-05-002-0001 Water Impact Analysis
13-05-002-0002 Sewer Impact Analysis
13-05-002-0003 Transportation Impact Analysis
13-05-002-0003.1 General
13-05-002-0003.2 Process
13-05-002-0003.3 Requirements
13-05-002-0003.4 Analysis Methods and Report Format
13-05-002-0003.5 Study and Report Format
13-05-002-0004 Stormwater Impact Analysis
13-05-002-0001 Water Impact Analysis
The City of Flagstaff shall prepare the water impact analysis that is required as part of the submittal process for any development that involves: an annexation, extension of service beyond the urban growth boundary, specific or small area plan, development master plan, subdivision plat, change of zoning request (medium or large in accordance with the zoning code), main extension, or a site plan submittal for any development which will generate a peak hour demand greater than the equivalent flow of ten (10) single-family dwelling units (the requirement may be waived at the discretion of the City Engineer and the Utilities Director).
A. The analysis shall establish the parameters of the system which satisfies the requirements of Division 13-09-003, Water System Design.
1. The analysis shall evaluate the maximum daily rate plus the required flow rate for fire protection, and the maximum hourly rate to determine which will govern the design.
2. The system analysis shall include the development, as well as adequate surrounding areas to determine that the new development will not negatively impact adjacent developments and the encompassing water pressure zone.
3. All calculations should be shown to justify the design.
4. Approval of any proposed development will require the correction of any deficiencies indicated in the report by the developer, including inadequate flow to the development.
B. This analysis need not be made if the site has previously been included in a complete water impact analysis for a larger area and the land use and intensity assumed for the site in that previous analysis is the same as that of the proposed development.
C. A computer model of the proposed water system for the development will be performed by the City for a fee that is separate from the development plan review fee.
1. Adequate information regarding the project’s water demands must be provided by the developer to the City, in order to run the model.
2. The information provided will determine the upper limit of demand that the development may place on the water system.
3. In the event that a proposed development exceeds the maximum demand, as determined in the impact analysis, a new water impact analysis may be required.
4. The model will determine the impact of the development on the City’s water system as well as the impact of the City’s water system on the development.
D. The analysis and report shall be submitted with the development application. (Ord. 2017-22, Rep&ReEn, 07/05/2017)
13-05-002-0002 Sewer Impact Analysis
The City of Flagstaff shall prepare, at the expense of the developer, a sewer impact analysis that is required as part of the submittal for any development that involves: an annexation, extension of service beyond the urban growth boundary, specific or small area plan, development master plan, subdivision plat, change of zoning request, medium or large in accordance with the zoning code), main extension, or a site plan submittal for any development which will generate a peak hour discharge greater than the equivalent flow of ten (10) single-family dwelling units (the requirement may be waived at the discretion of the City Engineer and the Utilities Director).
A. All general requirements, as listed in Division 13-09-002, Sewer System Design, shall be adhered to.
1. The developer must provide adequate information regarding the project’s sewer discharge to the City, in order to run the model.
a. The information provided will determine the upper limit of discharge that the development may place on the sewer system.
2. In the event that a proposed development exceeds the maximum discharge, as determined in the impact report, a new sewer impact analysis may be required.
3. The model will determine the impact of the development on the City’s sewer system. However, the computer model will not address the functionality of the development’s sewer system.
B. The analysis and report shall be submitted with the development submittal application.
C. The analysis shall include the following: estimate of flows generated from the proposed development, capacity of existing downstream mains from the tie-in point of the development to the Rio de Flag sewer trunk line, and the impact development flows will have on these downstream mains.
1. The calculated off-site impacts shall be based on a steady-state flow pattern using the peak flows established in Chapter 13-09 (the loadings and patterns may be modified at the discretion of the Utilities Director).
2. The Rio de Flag sewer trunk line shall be defined as the sewer line between manhole R-065 and manhole 23-001.
3. Approval of any proposed development will require the correction of any deficiencies by the developer to any off-site mains between the development and the nearest downstream treatment plant.
D. The analysis need not be made if the site has previously been included in a complete sewer impact analysis for a larger area and the land use and intensity assumed for the site in that previous analysis is the same as that of the proposed development. (Ord. 2017-22, Rep&ReEn, 07/05/2017)
13-05-002-0003 Transportation Impact Analysis
13-05-002-0003.1 General
A. The impact of traffic generated by new developments and re-developments on the City’s transportation network shall be considered in the approval process for all developments. The purpose for this consideration will be to:
1. Determine the transportation impacts of the project on the existing and future public transportation networks and identify measures to mitigate these impacts.
2. Highlight any special or unusual transportation conditions which may exist and describe how they will be handled.
3. Provide sufficient information for an assessment of the fair costs to mitigate the impacts of the development.
4. Coordinate circulation aspects of the project with those of other projects, existing developments, and the City’s general and specific plans.
5. Ensure uniform requirements and treatment for all developers.
6. Provide data for the City’s ongoing capital improvement and long range planning programs.
B. The analysis and report shall be prepared under the supervision of a professional engineer (civil) registered in the State of Arizona. The report shall be sealed and signed. (Ord. 2017-22, Rep&ReEn, 07/05/2017)
13-05-002-0003.2 Process
The City Traffic Engineer shall approve the level, scope, and impact area for the analysis for each project, as well as any special conditions and issues to be addressed. The Engineering Section Project Manager will communicate the analysis requirements to the developer and/or the developer’s engineer at the first concept review meeting where the project is considered.
A. Acceptance by the City of the TIA shall be a condition of approval of a development project as follows:
1. For annexation, general area plan, specific plan, subdivision plat, or change of zoning request (medium or large) in accordance with the zoning code, the analysis must be accepted prior to staff scheduling the project for Planning and Zoning Commission for public hearing, or prior to staff approval of a development agreement, whichever comes first.
2. For individual development types not included in the previous categories, the analysis must be accepted prior to site plan approval. (Ord. 2017-22, Rep&ReEn, 07/05/2017)
13-05-002-0003.3 Requirements
The need and level of analysis for a TIA shall be based on the number of vehicle trips generated by the development during the peak hour. The criteria for determining the analysis category, study horizon, and minimum study area are summarized in Table 13-05-002-01.
A. Category 0 – Very Small Developments. A traffic impact analysis may be required for developments that generate fewer than one hundred (100) peak hour directional trips. The requirement will be based on existing or anticipated special conditions or traffic problems near the site that may be aggravated by the development. The analysis shall address the impact of the development with respect to these conditions.
B. Category 1 – Small Developments. A Category 1 analysis is required for developments that generate between one hundred (100) and five hundred (500) peak hour directional trips. The analysis will generally focus on site access and the impact of the development on the adjacent circulation network.
C. Category 2 – Moderate or Large Developments. A Category 2 analysis is required for developments that generate more than five hundred (500) peak hour directional trips. The analysis will cover the circulation system within the influence area of the development and may include analysis at different future stages of the project.
D. Exceptions. Very small developments will often be excepted from the requirement of a full traffic impact analysis. The City Engineer’s scoping statement will serve for the development approval requirement.
Developments that have been anticipated in a previously accepted analysis may be excepted from the requirement to perform a full analysis; provided, that the proposed development substantially complies with the conditions and assumptions made for the transportation impacts of that development in the original analysis. These conditions and assumptions would include land use type and intensity, trip generation and distribution, site configuration and access points, and adjacent roadway configuration and traffic conditions. Special conditions or traffic problems near the site may require an analysis to address the impact of the development with respect to these conditions.
E. Coordination with Arizona Department of Transportation (ADOT). The developer of any project that has access to or frontage upon a State highway within the City limits shall contact the assigned ADOT Traffic Engineer in order to determine the Department’s impact analysis requirements for the project. To the extent that these exceed the City’s requirements, they shall be incorporated into the scope of the analysis required by the City. The intent here is that the developer is required to perform only a single TIA that satisfies the requirements of both agencies.
|
ANALYSIS CATEGORY |
DEVELOPMENT CHARACTERISTICS |
STUDY HORIZON |
MINIMUM STUDY AREA |
|---|---|---|---|
|
0 |
Very Small Development <100 peak hour directional trips |
City Engineer shall set or waive requirements for traffic analysis for very small projects on a case-by-case basis |
|
|
1 |
Small Development 100 - 500 peak hour directional trips |
Opening year |
- Site access drives and adjacent streets |
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- Adjacent signalized and/or major street intersections |
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|
2-M |
Moderate, single phase 500 – 1,000 peak hour directional trips |
Opening year |
- Site access drives and adjacent streets |
|
- Street network and major intersections within 1/2 mile |
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|
2-L |
Large single phase > 1,000 peak hour directional trips |
Opening year City planning horizon year |
- Site access drives and adjacent streets |
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- Street network and major intersections within 1 mile |
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2-MULTI |
Moderate or large, multi-phase |
Opening year of each phase City planning horizon year |
- Site access drives and adjacent streets |
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- Street network and major intersections within 1 mile |
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(Ord. 2017-22, Rep&ReEn, 07/05/2017)
13-05-002-0003.4 Analysis Methods and Report Format
A. Study Area and Study Horizon Years. The minimum study area and the horizon years for the study shall be determined by the project size and type based on Table 13-05-002-01. The City Engineer may determine that the study area and horizon shall be adjusted based on the following conditions:
1. Special traffic conditions or capital projects underway which may exist outside the minimum study area but which will be affected by the project’s traffic.
2. Coordination with and accounting for the impact of other development projects in the vicinity of the development which contribute traffic to the street network in the geographic area of the traffic impact analysis.
B. Analysis Time Period. In most cases only the afternoon weekday peak period shall be analyzed. This may be varied if:
1. The proposed project is expected to generate very few trips during the weekday evening peak, in which case the peak hour of generation for the project shall also be analyzed; or
2. The peak traffic hour on the streets in the study area occurs during a different time period, such as noon, morning, or weekend, in which case that period shall also be analyzed.
C. Data Collection. All data shall be collected in accordance with the latest edition of the ITE Manual of Traffic Engineering Studies or as directed by the City Engineer. Existing traffic volume studies may be extrapolated for a period of two (2) years, with the concurrence of the City Engineer, in lieu of performing a required study.
1. Turning Movement Counts at Intersections and Driveways. Turning movement counts shall be obtained for all existing cross-street intersections and major driveways to be analyzed during the analysis time period. Turning movement counts at other times may also be required. These counts shall include classification of pedestrians, and bikes.
2. Traffic Volumes. Current and projected daily traffic volumes shall be presented in the report for all streets within the study area. A directional mechanical count for a minimum forty-eight (48) hours shall be made at each location. The data shall be taken in fifteen (15) minute increments.
3. Accidents. An analysis of accidents and the impact of the development on the accident patterns may be required.
4. Street and Intersection Geometry. Roadway and intersection geometric information for existing and future streets and intersections shall be obtained. This shall include width, number of lanes, turning lanes, vertical grade, location of driveways, vertical and horizontal geometry, and sight distance.
5. Existing Traffic Control Devices. The location and type of traffic control devices adjacent to the development, including pavement markings, signs, and signals shall be identified. All traffic signals within the study area shall be identified along with their phasing, timing, and coordination programs.
6. Other information may be required in order to perform a complete analysis including but not limited to:
a. Transit routes and stops;
b. Pedestrian generators and circulation patterns;
c. Bicycle facilities;
d. Emergency response time.
D. Trip Generation. Trip generation shall be developed using the latest edition of ITE’s Trip Generation. Other sources may be used with the approval of the City Engineer if the ITE manual does not include trip rates for a specific category of land use, or if the local trip generation rates have been shown to differ from the ITE rates.
E. Distribution and Assignment. Projected trips shall be distributed to the street network and added to the projected nonsite traffic within the study area.
1. The specific assumptions and data sources used in deriving trip distribution and assignment shall be documented.
F. Capacity Analysis.
1. Level of service shall be computed for all signalized and main unsignalized intersections within the study area. Level of service at site driveways shall also be computed. Level of service shall be determined in accordance with the latest edition of the Highway Capacity Manual.
2. Queue lengths for dedicated turn lanes at signalized intersections shall be determined.
G. Improvement Analysis. A traffic signal needs study shall be conducted for any new signal proposed for the development.
1. The study shall identify when the signal will be warranted, and the conceptual design for the signal and its operation.
2. The report shall identify the steps to be taken to mitigate any adverse effects of the traffic generated by the development on the street network within the study area.
a. This shall include, but not be limited to:
(1) Improvements to existing signalized and unsignalized intersections.
(2) Future signalization of unsignalized intersections.
(3) Maintenance of street capacity at site driveways.
b. Where the impact to be mitigated is less than the capacity improvement created by the mitigation, then sufficient information to determine a fair proportional distribution of cost to the developer for the mitigation shall be presented. (Ord. 2017-22, Rep&ReEn, 07/05/2017)
13-05-002-0003.5 Study and Report Format
Full documentation of the analysis is required in the report. The report format should be scaled to the required category of the analysis. Table 13-05-002-02 shows the minimum requirements for inclusion in the report for each level of analysis.
|
ANALYSIS CATEGORY |
0 |
1 |
2-M |
2-L |
2-MULTI |
|---|---|---|---|---|---|
|
INCLUSION |
|
|
|
|
|
|
INTRODUCTION |
|
X |
X |
X |
X |
|
EXECUTIVE SUMMARY |
|
|
X |
X |
X |
|
PROJECT DESCRIPTION |
X |
X |
X |
X |
X |
|
SITE PLAN |
|
|
X |
X |
X |
|
PHASING AND TIMING |
|
|
X |
X |
X |
|
STUDY AREA CONDITIONS |
|
|
|
|
|
|
EXISTING AND ANTICIPATED LAND USE |
|
X |
X |
X |
X |
|
EXISTING AND FUTURE ROAD-WAY SYSTEM |
|
X |
X |
X |
X |
|
EXISTING OPERATIONS |
|
|
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|
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ROADWAY CONDITIONS AND TRAFFIC CONTROLS |
|
|
X |
X |
X |
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OTHER MODES |
|
|
X |
X |
X |
|
TRAFFIC VOLUMES |
|
|
X |
X |
X |
|
LEVEL OF SERVICE |
|
|
X |
X |
X |
|
SAFETY |
|
|
X |
X |
X |
|
PROJECTED TRAFFIC* |
|
|
|
|
|
|
SITE TRAFFIC |
X |
X |
X |
X |
X |
|
NONSITE TRAFFIC |
|
X |
X |
X |
X |
|
TOTAL TRAFFIC |
|
X |
X |
X |
X |
|
TRAFFIC AND IMPROVEMENT * ANALYSIS |
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SITE ACCESS |
|
X |
X |
X |
X |
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LEVEL OF SERVICE ANALYSIS |
|
X |
X |
X |
X |
|
ROADWAY IMPROVEMENTS |
|
X |
X |
X |
X |
|
DRIVEWAY OPER. ANALYSIS |
|
|
X |
X |
X |
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ALTERNATE MODES |
|
X |
X |
X |
X |
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TRAFFIC CONTROL NEEDS |
|
X |
X |
X |
X |
|
TRAFFIC SIGNAL NEEDS |
|
X |
X |
X |
X |
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CONCLUSIONS |
|
X |
X |
X |
X |
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RECOMMENDATIONS |
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|
X |
X |
X |
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APPENDICES |
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|
X |
X |
X |
* For multi-phase developments projected traffic and the traffic and improvements analysis shall be made for each phase of the development and for the City’s planning horizon.
(Ord. 2017-22, Rep&ReEn, 07/05/2017)
13-05-002-0004 Stormwater Impact Analysis
A stormwater impact analysis shall be required for a general plan amendment or a request for a zoning change. When required, the following shall be provided in a report for review and approval.
A. Calculations for pre- and post-development runoff volumes.
B. Downstream impacts as the result of increased volumes shall be assessed as scoped by the City’s Stormwater Management Section and may include:
1. Hydrologic calculations to determine discharges at various downstream points pre- and post-development.
2. Corresponding hydraulic calculations to determine any increase in water surface elevations.
3. A geomorphic analysis to determine channel stability and sediment transport concerns as the result of increased flow duration created by increased volumes and clear water runoff created by development.
4. Other hydrologic and hydraulic calculations necessary to determine and resolve impacts.
C. Water surface increases may be allowed; provided, that they are less than one-tenth (1/10) of one (1) foot (0.1 feet) and there are no structures with known or calculated flooding problems or other major concerns. Water surface increases for Lake Continental, aka Big Fill Lake, (impoundment located on the Rio de Flag upstream of Route 66/I-40) are prohibited. (Ord. 2017-22, Rep&ReEn, 07/05/2017)