Calculator Inputs
Example Data Table
| Scenario | Input | Input measure | Key result | Result measure |
|---|---|---|---|---|
| Corridor daily to per-lane design flow | 25,000 | AADT (veh/day) | 572.917 | Per-lane peak direction DHV (veh/hr/ln) K=0.10, D=0.55, L=2 |
| 15‑minute peak to peak-hour volume | 260 | Peak 15‑min count (veh/15‑min) | 956.800 | Peak direction DHV (veh/hr) PHF=0.92 |
| Peak direction to PCU rate | 1,200 | Peak direction DHV (veh/hr) | 1,332.000 | PCU per hour (pcu/hr) 85% PC, 10% truck (1.5), 3% bus (2.0), 2% MC (0.5) |
Formulas Used
- Design hour volume: DHV(two‑way) = K × AADT
- Peak direction share: DHV(peak dir) = D × DHV(two‑way)
- Per‑lane conversion: DHV(per lane) = DHV(peak dir) ÷ L, where L is lanes per direction.
- Peak hour factor relation: PHF = Vhour ÷ (4 × V15), so Vhour = PHF × 4 × V15.
- Rate conversions: veh/min = veh/hr ÷ 60, veh/sec = veh/hr ÷ 3600.
- PCU conversion: PCU/hr = veh/hr × wPCE, where wPCE = Σ(share% × PCE) / 100.
How to Use This Calculator
- Enter your known traffic volume and select the correct Input measure.
- Select the Output measure you need for analysis or reporting.
- Provide corridor factors: K (design hour share), D (peak direction split), and L (lanes per direction).
- If using 15‑minute counts, set an appropriate PHF.
- For PCU outputs, adjust vehicle composition and PCE values.
- Click Convert to view results below the header and above the form.
- Use Download CSV or Download PDF for deliverables.
Practical Guide to Traffic Volume Conversions
1) Why consistent units matter
Traffic data is collected in many formats: daily counts (AADT), short-duration turning counts, or continuous detector streams. Converting everything to a comparable base—often peak-direction, per-lane vehicles per hour—reduces design risk and keeps reports auditable.
2) Daily to design-hour planning using K
The K factor estimates the share of daily traffic occurring in the design hour. For example, with AADT 25,000 and K 0.10, the two-way DHV is 2,500 veh/hr. This is the starting point for lane-level checks and intersection sizing.
3) Directional split and lane distribution
The D factor converts two-way DHV into the peak direction demand. If D is 0.55, then 2,500 veh/hr becomes 1,375 veh/hr in the peak direction. With two lanes per direction, that is 687.5 veh/hr/ln—useful for LOS screening and capacity comparisons.
4) Short counts and PHF for peak realism
Short counts often capture the busiest 15 minutes. PHF links that burstiness to an hourly equivalent. With PHF 0.92 and a peak 15-minute count of 260 veh/15-min, the peak-hour volume becomes 956.8 veh/hr. This helps avoid underestimating queues and merge turbulence.
5) PCU outputs for mixed traffic corridors
Mixed vehicle streams require a passenger car equivalent approach when heavy vehicles influence operations. The calculator computes a weighted PCE from composition and factors, then converts veh/hr to PCU/hr. This supports corridor studies where trucks and buses disproportionately affect speed, headways, and saturation flow.
For best practice, document the factors you selected, the data source, and the survey period. Use the CSV or PDF exports to attach assumptions to drawings, traffic impact studies, or design memos. Consistent reporting improves review turnaround and reduces rework.
FAQs
1) What is AADT and when should I use it?
AADT is the average number of vehicles per day over a year, typically two-way. Use it for corridor planning, long-term forecasts, and when only daily totals are available.
2) What does the K factor represent?
K is the fraction of daily traffic that occurs during the design hour. It converts AADT to two-way DHV and should reflect local patterns, seasons, and facility type.
3) How do I choose the D factor?
D is the peak-direction share of the two-way design hour. Commuter routes often have higher directional imbalance. Use measured directional counts when possible; otherwise apply a conservative corridor assumption.
4) What is PHF and why does it matter?
PHF accounts for within-hour peaking. Lower PHF means sharper peaks and more operational stress. It converts a 15-minute peak count to an hourly equivalent for capacity, queue, and ramp analyses.
5) Why are “lanes per direction” required?
Per-lane results are based on peak-direction volume divided by the number of lanes serving that direction. This makes comparisons consistent across corridors with different cross-sections.
6) What are PCU and PCE values used for?
PCU represents equivalent passenger cars. PCE factors assign heavier vehicles a larger operational impact. The calculator applies a weighted PCE to convert veh-based rates into PCU-based rates.
7) Why don’t my percentages need to total 100?
If your composition percentages do not sum to 100, the calculator automatically normalizes them. This avoids accidental bias from data entry while preserving the intended vehicle mix proportions.