Chapter 18.40


18.40.010    Traffic impact analysis requirements.

18.40.020    Traffic impact analysis guidelines.

18.40.010 Traffic impact analysis requirements.

Applicants for development and redevelopment projects expected to create 20 or more residential units (e.g., single family residential lots, apartment/condo units) or 20,000 square feet or more of commercial/industrial space shall evaluate the project’s transportation system impacts in a transportation impact analysis (TIA). The TIA is used to determine a project’s impacts to the City’s transportation system. The City requires that the TIA be prepared by a licensed transportation engineer in the State of Oregon and follow the City’s current TIA guidelines. The recommended general format is as follows and pertains to City of Coos Bay facilities. Oregon Department of Transportation (ODOT) facilities should be addressed with ODOT using ODOT criteria.

1. A TIA shall analyze the ultimate build out of the project.

2. Any intersection where the proposed development can be expected to contribute 25 or more trips during the analysis, peak hour shall be included in the study area and evaluated operationally to determine compliance with City performance standards.

3. Development trip generations shall utilize the most recent edition of the Institute of Transportation Engineers (ITE) Trip Generation to estimate daily and peak hour trips to/from the development. All assumptions and adjustments regarding pass-by, diverted link, and internal trips shall be calculated in accordance with ITE methodology and documented in the analysis.

4. Trip distributions into and out of the transportation system must either follow existing traffic patterns or use a current transportation model. If alternate splits are used to distribute development trips, then justification must be provided and approved by the City prior to submittal of the TIA.

5. Turning movement counts where signal modifications or signals are being proposed shall be a minimum of 12-hours long, with 15-minute breakdowns in the A.M. and P.M. peak hours, unless pre-approved for a lesser time. For all other intersections, counts shall be at least 2-hours long and taken during the A.M. and P.M. peak periods, with 15-minute breakdowns. Counts must be no longer than two years old to be applicable.

6. All traffic volumes shall be seasonally adjusted to represent peak conditions in accordance with ODOT’s Analysis Procedures Manual (APM).

7. Level of service analyses shall follow operational procedures per the current Highway Capacity Manual (HCM). Ideal saturation flow rates greater than 1800 vehicles per hour per lane shall be justified by field measurements. Queue lengths reported in the analysis shall be 95th percentile lengths and rounded to the nearest 25' increment, in accordance with ODOT’s APM. Actual peak hour factors shall be used for existing conditions and calculated for each intersection or approach depending upon the peaking characteristics of an intersection. For new intersections, default peak hour factors shall be used in accordance with ODOT’s APM.

8. Intersection sight distance shall be evaluated at all site driveways and proposed new approaches in accordance with the American Association of State Highway and Transportation Officials (AASHTO) Policy on Geometric Design methodologies. Right and left turn lane criterion shall be evaluated at site driveways and proposed new approaches in accordance with ODOT’s APM.

9. Stop-controlled intersections shall be evaluated for signal warrants per the Manual on Uniform Traffic Control Devices (MUTCD) if the level of service is determined to be below performance standards. Left and right turn lanes shall also be evaluated where failing facilities are identified and none are currently provided.

10. Analyses shall include existing, design, and future year (City’s Transportation System Plan future year) scenarios. For phased developments, analyses shall be evaluated for each phase of development.

11. The TIA shall determine all improvements and/or mitigation measures necessary to meet City performance standards. For each phase of development, improvements shall be identified to accommodate additional traffic generated by this project.

The TIA format shall follow the City’s Traffic Impact Analysis Guidelines provided on the following pages of this Appendix.

[Ord. 479 § 1 (EDS Appendix B), 2016].

18.40.020 Traffic impact analysis guidelines.


1) Introduction and Summary

a) Purpose of the report and study objectives

b) Executive summary

(1) Site location and study area

(2) Development description

(3) Principal findings

(4) Conclusions

(5) Recommendations

2) Proposed Development

a) Site location

b) Land use and intensity

c) Site plan (readable version shall be provided)

(1) Access geometrics

d) Development phasing and timing

3) Study Area Conditions

a) Study area

(1) Area of significant traffic impact

(2) Influence area

b) Land use

(1) Existing land use

(2) Anticipated future development

c) Site accessibility

(1) Existing and future area roadway system

4) Analysis of Existing Conditions

a) Physical characteristics

(1) Roadway characteristics

(2) Traffic control devices

(3) Transit service

(4) Pedestrian/bicycle facilities

(5) Existing transportation demand management

b) Traffic volumes

(1) Daily, morning, and afternoon peak periods (two hours), and others as required

c) Level of service

(1) Morning peak hour, afternoon peak hour, and other as required

d) Safety

e) Data sources

5) Projected Traffic

a) Site traffic forecasting (each horizon year)

(1) Trip generations

(2) Mode split

(3) Pass-by traffic (if applicable)

(4) Trip distribution

(5) Trip assignment

b) Non-site traffic forecasting (each horizon year)

(1) Projections of non-site traffic by ODOT or other source. For larger developments and study areas, a more comprehensive method may be required which includes: trip generation, trip distribution, modal split and trip assignment.

c) Total traffic (each horizon year)

6) Traffic and Improvement Analysis

a) Site access

b) Level of service analysis

(1) Without project including programmed improvements (each horizon year)

(2) With project including programmed improvements (each horizon year)

c) Roadway improvements

(1) Improvements programmed by the City of Coos Bay, ODOT or others to accommodate non-site traffic

(2) Additional alternative improvements to accommodate site traffic

d) Traffic Safety

(1) Sight distance

(2) Acceleration/deceleration lanes, left-turn lanes

(3) Adequacy of location and design of driveway or site access

e) Pedestrian considerations

f) Speed considerations

g) Traffic control needs

h) Traffic signal needs (base plus each year in five-year horizon)

i) Conformance with the City of Coos Bay Transportation System Plan

7) Conclusions

8) Recommendations

a) Site access

b) Roadway improvements

(1) Phasing

c) Conformance with the City of Coos Bay Transportation System Plan

d) Other

9) Appendices

a) Traffic counts

b) Capacity analyses worksheets

c) Traffic signal needs studies

d) Accident data and summaries

The traffic impact analysis shall be prepared under the supervision of a Professional Traffic Engineer or qualified Civil Engineer registered in the State of Oregon. The report shall be sealed and signed by the engineer.

The latest edition of the Institute of Transportation Engineers’ “Trip Generation” shall be used for selecting trip generation rates.

All assumptions shall be discussed in the study narrative. All data sources shall be referenced and all supporting data will accompany the study.

[Ord. 479 § 1 (EDS Appendix B), 2016].