Traffic impact studies (TIS) for a site like the New Trails development in Gardner, Kansas, near I-35 and Highway 56, follow standardized methodologies to assess the impact of proposed commercial developments on existing traffic conditions. These studies are critical given I-35’s high volume of 40,000 vehicles per day (Valbridge Property Advisors, January 2024), historical congestion at the Gardner Road exit, and planned infrastructure upgrades like the $25 million I-35/U.S. 56 interchange modernization (KDOT, March 2024). Below are the key methodologies typically employed in such studies, tailored to the context of New Trails.
1. Study Area Definition
- Methodology: Identify the geographic scope impacted by the development, including key intersections, road segments, and access points. For New Trails, this includes I-35, Highway 56, Gardner Road, and Clare Road (noted as a potential access point in the Valbridge report).
- Application: The study area would encompass the I-35/U.S. 56 interchange, where KDOT’s modernization project is planned, and nearby intersections like Gardner Road, known for congestion (Kansas City Star, 2017). The 40,000 vehicles/day on I-35 and Highway 56’s 10,000 vehicles/day (Valbridge) set the baseline traffic load.
2. Existing Conditions Analysis
- Methodology: Collect data on current traffic volumes, peak-hour flows, crash history, and roadway characteristics using:
- Traffic Counts: Manual counts or automated traffic counters to measure vehicle volumes, typically over a 24-hour period and during peak hours (e.g., 6:30–7 a.m., as noted for Gardner Road congestion).
- Level of Service (LOS): Assess intersection and roadway performance using the Highway Capacity Manual (HCM) methodology, grading from A (free flow) to F (severe congestion).
- Crash Data: Analyze accident history to identify safety concerns, often sourced from local police or DOT records.
- Application: For New Trails, existing conditions would show I-35’s 40,000 vehicles/day, with peak-hour backups at Gardner Road (2017 Kansas City Star). Crash data might include recent incidents like the February 2024 semi-truck fire or April 2024 police chase near Moonlight Road. LOS analysis would likely reveal poor performance (e.g., LOS D or worse) at Gardner Road during peak hours due to left-turn delays.
3. Trip Generation Estimation
- Methodology: Estimate the number of new trips generated by the proposed development using the Institute of Transportation Engineers (ITE) Trip Generation Manual. This involves:
- Land Use Categories: Assign trip rates based on development type (e.g., retail, restaurant, hotel).
- Trip Rates: Apply ITE rates for daily and peak-hour trips, adjusting for local conditions (e.g., pass-by trips for retail).
- Application: The New Trails plan (J2J New Trails, LLC, April 2025) includes a C-Store (1.50 acres), coffee shops (2.00 acres), restaurants (3.00 acres), retail (9.00 acres), and a hotel (2.50 acres). Using ITE rates:
- A C-Store (convenience store with gas) might generate ~700 trips/day per 1,000 sq ft (e.g., 5,000 sq ft = 3,500 trips/day).
- Coffee shops (e.g., 2,000 sq ft each) could generate ~200 trips/day each, with high AM peak-hour trips.
- Restaurants (e.g., 5,000 sq ft each) might generate ~500 trips/day each.
- Retail (e.g., 40,000 sq ft strip) could add ~1,500 trips/day, with pass-by reductions.
- A hotel (e.g., 100 rooms) might generate ~800 trips/day. Total new trips could exceed 10,000 daily, with ~1,000–1,500 during peak hours, significantly impacting I-35 and Highway 56.
4. Trip Distribution and Assignment
- Methodology: Determine where trips will originate and how they’ll travel through the network:
- Distribution: Use regional travel patterns, often based on a gravity model or local surveys, to allocate trips (e.g., 60% from I-35 north, 30% south, 10% local via Highway 56).
- Assignment: Map trips onto the road network using traffic modeling software (e.g., VISSIM, Synchro) to predict turning movements and impacts on intersections.
- Application: For New Trails, most trips would likely access I-35 (40,000 vehicles/day) and Highway 56 (10,000 vehicles/day). A significant portion would be pass-by trips (e.g., retail customers already on I-35), but new trips from the hotel and restaurants would add to peak-hour loads, particularly at the I-35/U.S. 56 interchange and Clare Road access points.
5. Future Conditions Analysis (Without Development)
- Methodology: Forecast background traffic growth without the proposed development, typically over a 5–20-year horizon:
- Growth Rates: Apply annual growth rates (e.g., 1–2% per year, based on historical data or regional plans).
- Planned Improvements: Incorporate infrastructure projects like KDOT’s I-35/U.S. 56 interchange modernization (FY2029, KDOT 2024).
- LOS Analysis: Recalculate LOS for future conditions using HCM methods.
- Application: Gardner’s 4.89% population growth in 2023 (U.S. Census Bureau, May 2024) suggests a traffic growth rate of ~2–3% annually. Without New Trails, I-35 might see 44,000–48,000 vehicles/day by 2030. The KDOT interchange project would improve LOS, but Gardner Road’s historical congestion (LOS D/F in 2017) could worsen without further mitigation.
6. Future Conditions Analysis (With Development)
- Methodology: Add the development’s trips to the future background traffic and reassess impacts:
- Total Traffic: Combine background growth with New Trails’ 10,000+ daily trips.
- LOS and Delay: Recalculate LOS, focusing on intersections like I-35/U.S. 56 and Gardner Road, using HCM or simulation tools (e.g., Synchro).
- Safety Analysis: Evaluate increased crash risks due to higher volumes, referencing historical data (e.g., 2017 safety concerns, 2024 incidents).
- Application: New Trails’ 1,000–1,500 peak-hour trips could push I-35/U.S. 56 and Gardner Road to LOS E/F during peak hours, exacerbating delays. Left-turn movements at Gardner Road, already problematic (2017 Kansas City Star), would face increased strain, potentially raising crash risks without mitigation.
7. Mitigation Measures
- Methodology: Propose solutions to address identified impacts, ensuring LOS remains acceptable (typically LOS D or better in urban areas):
- Roadway Improvements: Add lanes, turn lanes, or roundabouts.
- Signalization: Install or retime traffic signals to optimize flow.
- Access Management: Design site access to minimize conflicts (e.g., right-in/right-out only).
- Demand Management: Encourage carpooling or transit for employees.
- Application: For New Trails, mitigation might include:
- Signalization at Clare Road or Highway 56 access points (Valbridge notes access challenges being resolved with KDOT).
- Additional turn lanes at I-35/U.S. 56, aligning with KDOT’s modernization plans.
- A right-in/right-out design for the C-Store and retail to reduce left-turn conflicts.
- Coordination with KDOT’s diverging diamond interchange at Gardner Road (planned 2022 construction) to handle increased volumes.
8. Public and Agency Coordination
- Methodology: Engage stakeholders to validate findings and secure approvals:
- Public Input: Hold meetings to address community concerns, as seen in Johnson County’s 2024 rural road study (Web ID: 17).
- Agency Review: Submit the TIS to KDOT and local authorities (e.g., City of Gardner) for feedback, ensuring alignment with projects like the I-35/U.S. 56 interchange modernization.
- Application: Gardner residents have historically opposed traffic increases (e.g., South Metro Connection dropped in 2007). The TIS would need to address these concerns, emphasizing safety and the benefits of KDOT’s $25 million project, while coordinating with KDOT’s phased approach (concepts due fall 2025).
Summary
The traffic impact study for New Trails would use these methodologies to assess the addition of 10,000+ daily trips against I-35’s 40,000 vehicles/day and Highway 56’s 10,000 vehicles/day. It would reveal significant peak-hour impacts at Gardner Road and I-35/U.S. 56, necessitating mitigation like signalization, access management, and coordination with KDOT’s interchange project. Historical congestion, recent incidents, and public sentiment highlight the need for careful planning to ensure safety and efficiency.
