Complete Guide to Traffic Volume & Capacity Analysis
The Traffic Volume Calculator uses HCM 6 methods to estimate peak flows, directional splits, and LOS. Critical for signal warrants, lane additions, and traffic impact assessments. Integrates with Signal Timing and Road Curve tools.
What is Traffic Volume?
Number of vehicles passing a point in a given time. Key types:
- AADT: Annual Average Daily Traffic
- PHV: Peak Hour Volume
- DDHV: Design Directional Hourly Volume
Why Calculate It?
- Capacity Planning: Add lanes?
- Signal Design: Warrant analysis
- Safety: Congestion prediction
- Funding: Justify improvements
Key HCM 6 Equations
Peak Hour Volume
\( PHV = ADT \times \frac{K}{100} \)
Directional Design Hourly Volume
\( DDHV = PHV \times \frac{D}{100} \)
Flow Rate
\( v = \frac{DDHV}{PHF \times N \times f_{HV} \times f_P} \)
Level of Service (LOS)
| LOS | v/c Ratio | Description |
|---|---|---|
| A | ≤0.60 | Free flow |
| B | 0.61–0.70 | Reasonable flow |
| C | 0.71–0.80 | Stable flow |
| D | 0.81–0.90 | Approaching unstable |
| E | 0.91–1.00 | Unstable flow |
| F | >1.00 | Breakdown |
Step-by-Step Process
- Input ADT & K-factor
- Apply D & PHF
- Compute DDHV
- Estimate capacity
- Determine LOS
Example: Urban Arterial
ADT=15,000, K=10%, D=55%, PHF=0.90, 2 lanes:
- PHV = 1,500 veh/h
- DDHV = 825 veh/h/dir
- v = 458 pc/h/ln
- LOS = A
Typical Values
| Road Type | K (%) | D (%) | PHF |
|---|---|---|---|
| Urban Arterial | 9–12 | 55–60 | 0.88–0.95 |
| Rural Highway | 10–15 | 60–70 | 0.85–0.92 |
| Collector | 8–10 | 50–55 | 0.80–0.90 |
Applications
- Intersections: Signal warrants
- Highways: Lane justification
- Developments: Trip generation
- Transit: Bus lane feasibility
Best Practices
- Use tube counts or ATR data
- Apply seasonal factors
- Validate with Synchro/HCS
- Consider future growth
Common Mistakes
- Using ADT for peak design
- Ignoring PHF
- Wrong K or D factors
- Forgetting heavy vehicles
Advanced Topics
- Microsimulation (VISSIM)
- Adaptive signals
- Connected vehicles
- Complete streets
Conclusion
Accurate traffic volume analysis ensures safe, efficient roads. Our Traffic Volume Calculator delivers HCM-compliant PHV, DDHV, and LOS instantly. Pair with Signal Timing for complete intersection design. Plan smarter infrastructure!