Planning a new residential, commercial, or mixed-use development? One of the most critical steps in understanding its impact on surrounding roads and infrastructure is estimating how many vehicle trips it will generate. Whether you’re preparing a Traffic Impact Study (TIS), Traffic Impact Assessment (TIA), or just doing a preliminary feasibility analysis, getting your trip generation numbers right is essential.
In this step-by-step guide, we walk through how traffic engineers and urban planners estimate vehicle trips for proposed developments—using best practices, standard data sources, and tools like the Trip Generation Estimator Tool available on Arterials.
🚗 What Is Trip Generation?
Trip generation is the process of estimating the number of trips a development will produce (entering and exiting) during specific time periods—usually the AM and PM peak hours. It’s the first step in transportation impact analysis and lays the foundation for downstream steps like trip distribution, assignment, and mitigation planning.
📘 Step 1: Define the Land Use Type
Different land uses generate different traffic volumes. Start by identifying your development’s land use classification, such as:
- Residential (e.g., apartments, detached homes)
- Office or commercial buildings
- Shopping centers or mixed-use spaces
- Educational institutions
- Hospitals or medical offices
- Industrial or warehouse facilities
You’ll need this classification to reference standard trip rates.
📊 Step 2: Use Standard Trip Generation Rates
The most widely accepted source is the ITE Trip Generation Manual, published by the Institute of Transportation Engineers. It provides trip generation rates based on land use codes and thousands of real-world studies.
Example:
- ITE Code 210 – Single-Family Detached Housing
- ITE Code 820 – Shopping Center
Rates are typically provided in:
- Trips per dwelling unit
- Trips per 1,000 sq ft of gross floor area
- Trips per employee
You can also use tools like our Trip Generation Estimator which applies ITE-style logic based on simplified inputs.
🕒 Step 3: Focus on Peak Hour Trips
While daily trip totals are important, AM and PM peak hour estimates are most crucial for evaluating impact on traffic operations. These are the times when roadway networks are under maximum stress.
Your estimation should focus on:
- AM Peak Hour (7–9 AM)
- PM Peak Hour (4–6 PM)
🔁 Step 4: Account for Pass-By and Internal Trips (if applicable)
For retail or mixed-use developments, not all trips are “new” to the network. Some are:
- Pass-By Trips: Vehicles already on the road that stop into the development.
- Internal Capture Trips: Trips between land uses within the same development (e.g., residents walking to an on-site café).
Adjust your estimates accordingly using standard reduction rates (ITE provides these too).
🛣️ Step 5: Document Assumptions
Clearly list:
- Data sources (ITE Manual Edition, local data, etc.)
- Trip generation rates used
- Time periods (AM/PM peak)
- Any adjustments made (e.g., for internal capture)
This documentation is critical if your results are reviewed as part of a formal Traffic Impact Study. You can download a complete Traffic Impact Assessment Report template here.
🧰 Recommended Tools
Use the Trip Generation Estimator Tool on Arterials to get quick estimates based on your land use type and size. It’s designed for urban planners, engineers, and developers working in both preliminary and advanced stages. Also try the trip distribution tool.
⚠️ Limitations
- ITE data is based on North American studies—adjust for local context if needed.
- Mixed-use developments require careful coordination of internal capture effects.
- Future modal shifts (e.g., increase in transit, cycling, etc.) may not be reflected.
📞 Need a Professional Traffic Impact Study?
While this guide is a great starting point, actual TIA/TIS submissions often require professional validation. If you’re working on a development project and need traffic engineering support, get in touch with our team for tailored consulting.
🧠 Conclusion
Estimating vehicle trips may seem technical, but by following a systematic approach and using trusted data sources, you can get reliable numbers to move your project forward.
