10.0 Project Trip Generation
10.1.1 Trip Generation Sources
The project trip generation should be based on the latest edition of the Institute of Transportation Engineers (ITE) Trip Generation Manual. If data from the ITE Trip Generation Manual is unavailable or inappropriate for a project, other sources such as the San Diego Association of Governments (SANDAG) Traffic Generator's Manual or special trip generation studies can be utilized. These alternative sources should be presented to City staff for approval before the traffic study scoping agreement. For truck-intensive projects, trip generation figures should be converted to Passenger Car Equivalents (PCEs), and any trip credit for existing uses should be clearly identified.
10.1.2 Pass-by Trips
The use of pass-by trip adjustments may be permitted for applicable land uses, such as gas stations or fast-food restaurants, with approval through the traffic study scoping agreement. The ITE Trip Generation Handbook should be referenced for pass-by trip adjustments. However, for project access points and directly adjacent intersections, the full project trip generation should be used without pass-by trip reductions.
10.1.3 Internal Capture
For mixed-use projects, internal capture adjustments can be applied to avoid double-counting of trips. The ITE Trip Generation Handbook or other recognized sources may be used to determine trip reductions due to internal capture. This internal capture must be identified and approved within the scoping agreement.
10.1.4 Transit Adjustment
In most cases, no adjustments for public transit usage are made. However, certain projects located in areas with significant transit access may warrant transit-related trip reductions. Full documentation of any such reductions must be included in the traffic impact study and approved by the City.
11.0 Background Traffic
For project opening year conditions (with and without the project), the “build-up” method is typically used to project future traffic volumes. This involves applying an ambient growth rate to existing traffic counts. Additionally, any cumulative projects within two miles of the site must be considered in the analysis. A cumulative project is defined as one with a complete application, approval, or is under construction but not yet operational. The City's Planning Department can provide a list of such projects when scoping approval is requested. The project opening year is the timeframe when the development is expected to be fully built out and occupied. This year should be established and approved in the scoping agreement.
12.0 Capacity Analysis
Capacity analysis should be conducted for all project scenarios, assessing level of service (LOS) at signalized and unsignalized intersections, project driveways, and sometimes roadway segments. The LOS analysis should follow these guidelines:
12.1.1 Signalized Intersections (ICU Methodology)
- Use the Intersection Capacity Utilization (ICU) methodology to evaluate signalized intersections.
- A saturation flow rate of 1,700 vehicles per lane per hour should be assumed for all lanes, without adjustments for protected movements with dedicated lanes.
- A clearance interval factor of 0.05 should be applied, and a 100-second cycle time used for calculations.
12.1.2 ICU Level of Service Ranges
| Level of Service | Volume to Capacity Ratio | Description |
|---|---|---|
| A | 0.00 - 0.60 | Excellent operation, minimal delays. |
| B | 0.61 - 0.70 | Very good operation, occasional delay. |
| C | 0.71 - 0.80 | Good operation, fully utilized major approaches. |
| D | 0.81 - 0.90 | Fair operation, possible multiple red signals. |
| E | 0.91 - 1.00 | Poor operation, near capacity, long queues. |
| F | ≥1.00 | Forced flow, jammed conditions. |
12.1.5 Peak Hour Definitions
The peak-hour analysis should cover weekdays, specifically between 7:00 AM to 9:00 AM and 4:00 PM to 6:00 PM, with the highest consecutive hour used for calculations.
12.1.8 Right Turn Lane Considerations
If the distance between the edge of the outside lane and curb is 19 feet or greater, and parking is prohibited, right turns may be treated as using an unofficial right turn lane. Otherwise, right turn traffic is assumed to use the through lane.
12.1.9 HCM Methodology for Unsignalized Intersections
Unsignalized intersections, especially those controlled by stop signs on minor streets or project driveways, should be analyzed using the Highway Capacity Manual (HCM) methodology. The LOS should be determined based on the worst individual movement. For all-way stops, the average intersection delay should be used, while for cross-street stop conditions, the worst-case movement delay applies.
| HCM Level of Service | Signalized (Delay in Seconds) | Unsignalized (Delay in Seconds) |
|---|---|---|
| A | 0.00 - 10.00 | 0.00 - 10.00 |
| B | 10.01 - 20.00 | 10.01 - 15.00 |
| C | 20.01 - 35.00 | 15.01 - 25.00 |
| D | 35.01 - 55.00 | 25.01 - 35.00 |
| E | 55.01 - 80.00 | 35.01 - 50.00 |
| F | >80.00 | >50.00 |
For intersections controlled by Caltrans, both ICU and HCM methodologies must be applied.
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