4.0 Data Collection
A comprehensive and accurate data collection process is essential for conducting a Transportation Impact Study (TIS) in the City of Walnut Creek. The data collected should reflect current traffic conditions and inform the analysis of project-related impacts on the local transportation network. The following guidelines outline the procedures for gathering traffic data, including traffic counts and field observations, to ensure consistency and reliability in study findings.
4.1 Traffic Counts
New traffic counts must be conducted at each study intersection and roadway segment identified in the approved scope of work. These counts should capture peak-period turning movements for vehicles, bicycles, and pedestrians. All collected data should be included in the appendix of the final TIS report.
Existing traffic counts may be used if they are less than 24 months old and if no major changes—such as new developments, roadway modifications, or traffic control adjustments—have occurred that could significantly alter traffic patterns. The use of existing counts must be approved by City staff.
The following rules should be followed when conducting traffic counts:
- Timing of Counts:
- Weekday traffic counts should be performed on Tuesdays, Wednesdays, or Thursdays to ensure representative data.
- Counts should not be conducted on holidays, during the last two weeks of December, or in weeks containing a holiday.
- Weather and External Factors:
- Traffic counts should not be conducted in inclement weather.
- Data collection should be avoided during temporary road closures, construction projects, special events, or any incidents that could affect typical traffic flow.
- School Session Considerations:
- Counts should be conducted when schools and colleges are in session, but not during the first week of a new academic year.
- Peak Period Counts:
- Weekday intersection counts should be conducted from 7:00 a.m. to 9:00 a.m. for the morning peak period and from 4:00 p.m. to 6:00 p.m. for the afternoon peak period, unless specified otherwise.
- Counts should be recorded in 15-minute intervals, and the peak hour factor should be calculated.
- Special Considerations:
- Seasonal variations in traffic should be accounted for when necessary (e.g., near recreational areas or Downtown Walnut Creek).
- Weekend peak periods should be considered for certain land uses with high weekend traffic activity.
4.2 Field Observations
In addition to numerical data, qualitative observations should be made at study intersections and roadways during peak periods. Field observations provide context for the traffic analysis by identifying operational issues not evident in traffic counts. The consultant should document the following conditions:
- Freeway Ramp Effects: Assess the impact of freeway ramps on local streets, particularly ramp meter spillback.
- Lane Usage: Observe traffic lane distribution to identify uneven demand or inefficient use of available lanes.
- On-Street Parking: Evaluate whether parking activity affects traffic flow or safety.
- Pedestrian and Bicycle Safety: Identify safety issues for non-motorized users, including crossings and access points.
- Transit Routes and Stops: Note bus stops and transit services that could be impacted by project-generated traffic.
- Cut-Through Traffic: Determine if neighborhood streets experience increased cut-through traffic.
- Sight Distance Issues: Identify any visual obstructions that impact driver or pedestrian safety.
- Intersection Gridlock: Observe intersection congestion that may result in lower-than-expected traffic counts.
- Queueing and Storage Lengths: Measure queue lengths during peak hours to assess intersection performance.
- Truck Routes: Identify truck traffic patterns and potential conflicts with general traffic.
For locations experiencing prolonged congestion, consultants should record queue lengths at 15-minute intervals to capture changing traffic conditions.
The final TIS report should include a detailed description of all data collected, including specific dates, days of the week, and time periods for peak traffic counts. If existing data is used from a previous study, the source document should be cited. The appendix should contain all raw traffic count data to ensure transparency in the study’s methodology and findings.
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