Level-of-Service Analysis Procedure for Traffic Impact Analysis (TIA)
Introduction
A comprehensive Level-of-Service (LOS) analysis is required as part of the Transportation Impact Analysis (TIA) for new developments in the City of Buena Park. This analysis ensures that the proposed development does not cause significant traffic congestion or degrade the performance of the existing roadway network. Traffic studies must be prepared by qualified transportation planners or registered traffic engineers to maintain accuracy and reliability.
Traffic Data Collection
To establish an accurate baseline for analysis, traffic studies should include existing traffic counts at arterial highway links and peak-hour intersection counts in areas potentially affected by the proposed project. The LOS analysis should reflect the current operating conditions of these roadways and intersections, ensuring that the anticipated development traffic is appropriately assessed against the existing infrastructure capacity.
Traffic Generation, Distribution, and Assignment
Trip Generation
The City of Buena Park follows the trip generation rates established in the latest edition of the Institute of Transportation Engineers (ITE) Trip Generation Handbook. For land uses not covered in the ITE handbook, applicants may refer to alternative studies or trip rates from other agencies, provided they include supporting documentation for validation.
Internal Capture and Passer-By Traffic
If a development consists of multiple land uses, internal capture reductions should be justified based on credible methodologies, such as ITE or other approved studies. Passer-by trips should be estimated using ITE data or validated local studies.
Trip Distribution and Assignment
Trip distribution should be based on demographic and market data relevant to the area, considering factors such as the location of major employment centers, commercial hubs, and freeway access points. The methodology used for distribution can be either quantitative or qualitative, depending on the project size. Large-scale developments require a more detailed quantitative approach, potentially utilizing travel demand models.
Once fully developed, the City of Buena Park will require the use of its designated traffic model for determining trip distribution.
Trip assignment should account for the existing and projected roadway network, incorporating anticipated travel patterns and estimated travel times. The assignment process must factor in trip generation while subtracting the internal capture and passer-by traffic to accurately reflect project-related traffic movements.
The study should evaluate the impact of project traffic on all Congestion Management Program (CMP) roadways and arterial highways within the City until the projected effects fall below 3% of the capacity for Level of Service D on both roadways and intersections.
Traffic Forecasts
Traffic forecasts must consider the total anticipated traffic at the buildout phase of the proposed development. This includes cumulative traffic impacts from other planned or approved developments that have not yet been constructed.
Two methods can be used to develop future traffic forecasts:
- Historical Growth Factors – Applying growth trends to existing traffic volumes to estimate future demand.
- Approved and Pending Projects – Identifying potential additional traffic demand from specific development projects that are approved but not yet built.
To ensure consistency with regional planning efforts, traffic studies should use the latest version of the Orange County Transportation Analysis Model (OCTAM) for future-year traffic projections.
Traffic Analysis Methodology
Intersection Level of Service (LOS) Analysis
The City of Buena Park uses the Intersection Capacity Utilization (ICU) methodology to determine intersection LOS. This approach aligns with the latest edition of the Highway Capacity Manual (HCM) and includes the following parameters:
- Saturation Flow Rate: 1,700 vehicles per lane per hour. Adjustments may be made in cases where turn movements share lanes or lack protected signalization.
- Lost Time Factor: A 5% adjustment is applied in ICU calculations.
- Peak Hour Analysis: The defined weekday peak hour periods are:
- Morning (AM): 6:30 AM to 9:00 AM
- Evening (PM): 3:00 PM to 7:00 PM
- The highest one-hour period within these windows is used for analysis.
Traffic Count Collection
To ensure accuracy and consistency, traffic counts must be conducted under the following guidelines:
- Data collection should be avoided on Mondays, Fridays, weekends, or holidays unless the project is expected to generate traffic impacts specifically on those days.
- A minimum of three daily counts should be averaged for LOS calculations.
- Peak-hour analysis should be based on four consecutive 15-minute intervals to determine the highest volume one-hour period.
- Pedestrian impacts should be incorporated into the analysis using appropriate reductions in saturation flow rates, following HCM recommendations.
LOS Analysis Timeframes
The LOS analysis must evaluate traffic conditions for the following scenarios:
- Existing Conditions – Current traffic conditions without project influence.
- Opening Year Conditions – Traffic conditions expected in the project’s first operational year.
- Opening Year Plus Project – Traffic conditions in the opening year with project-generated traffic.
- Horizon Year Conditions – Traffic projections for a long-term future planning horizon (e.g., 20+ years).
- Horizon Year Plus Project – Traffic projections for the long-term horizon with project-generated traffic.
For large multi-phase developments, the City may require additional timeframes for phased impact assessments.
A summary table should be included in the traffic study, displaying the LOS results for all studied intersections under each scenario. The table should also outline any necessary mitigation measures to maintain acceptable LOS standards.
Arterial Highway Link Analysis
Determination of LOS for Arterial Roadways
Arterial highway classifications in the City’s Circulation Element follow the Highway Capacity Manual framework. A two-step process is used to determine LOS for arterial segments:
- Initial Screening: Compare observed Average Daily Traffic (ADT) against the roadway’s designated capacity to assess preliminary LOS.
- Detailed Analysis: If any segment operates at LOS E or worse, a secondary evaluation using SimTraffic or an alternative approved by the City Traffic Engineer is required.
This detailed analysis should involve field-measured segment lengths and average travel times, comparing results against the HCM methodology for determining LOS.
Transportation Effects and Mitigation
LOS Standards and Capacity Thresholds
A volume-to-capacity (V/C) ratio of 0.90 (LOS D) is the minimum acceptable service level for intersections.
The traffic study must quantify the following:
- Project Traffic Proportion: The share of projected traffic attributed to the proposed development at each intersection or roadway link.
- Project Impact on Capacity: The ratio of project-generated traffic to the intersection or roadway link’s capacity.
- Improvement Costs: A cost estimate for required mitigation measures, including:
- Planning and studies
- Design and engineering
- Right-of-way acquisition
- Construction and inspection
- Financing and funding strategies
Post-Mitigation LOS Evaluation
The final section of the TIA must document the projected LOS for all affected intersections and roadway segments after mitigation measures are implemented. This ensures that all transportation improvements effectively restore or maintain the required LOS thresholds.
The Level-of-Service analysis framework outlined in these guidelines ensures that all new developments in Buena Park undergo thorough traffic impact assessments. By evaluating both existing and projected traffic conditions, these procedures help maintain an efficient transportation system while aligning with the City’s long-term mobility goals.
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