Traffic Impact Study
An engineering analysis of how a proposed development will affect traffic on surrounding roads and intersections.
A Traffic Impact Study (TIS), also called a Traffic Impact Analysis (TIA), is an engineering study that evaluates how a proposed development will affect traffic conditions on the surrounding road network. Most municipalities require a TIS for any development that will generate a significant number of vehicle trips — thresholds vary but are typically 50 to 100 peak-hour trips.
What a Traffic Impact Study Includes
- Trip generation: How many vehicle trips the proposed development will create during peak hours and daily
- Trip distribution: Where those trips will come from and go to on the road network
- Level of service analysis: Current and projected performance of affected intersections and road segments
- Queuing analysis: Expected vehicle queue lengths at intersections and driveways
- Access analysis: Adequacy of proposed driveway locations, sight distances, and turning movements
- Mitigation recommendations: Road improvements, traffic signals, turn lanes, or other measures needed to maintain acceptable traffic conditions
- Multi-modal analysis: In some jurisdictions, pedestrian, bicycle, and transit impacts must also be evaluated
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How Traffic Studies Affect Development Approvals
Traffic impact studies frequently become the most contentious element of the development approval process. If the study identifies significant traffic impacts, the developer may be required to:
- Build or fund road improvements (turn lanes, traffic signals, road widening) - Reduce the project's size or density to lower trip generation - Implement Transportation Demand Management (TDM) strategies - Pay proportionate share contributions to planned road improvements
Why This Matters for CRE
Traffic mitigation requirements can add millions to development costs and fundamentally change project economics. A required road improvement that costs $2 million on a 100-unit apartment project adds $20,000 per unit to the development cost. Tracking traffic study submissions also reveals project details — the trip generation estimates indicate project size, while the study area reveals the geographic footprint of traffic impacts. For existing property owners, traffic studies for nearby developments may identify road improvements that benefit their access and visibility.
What to Watch For
- Concurrency requirements: In some jurisdictions, development cannot proceed until adequate road capacity exists or is funded
- Proportionate share obligations: Developers may be required to contribute to road improvements beyond their project boundaries
- Trip generation rates: Outdated ITE trip generation rates may overestimate traffic impacts, leading to excessive mitigation requirements
- Adjacent development cumulative impacts: Traffic studies must account for other pending developments, which can increase total mitigation costs
Related Terms
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