Roadway Level of Service Calculator

Inputs

Facility type

Density-based LOS applies to freeway/multilane selections.

LOS basis

Both chooses the worse LOS when available.

Units

Changing units will refresh default speed values.

Traffic volume (veh/h)

Use peak hour demand entering the segment.

Demand factor

Growth/seasonal multiplier (1.00 = none).

Peak hour factor (PHF)

Lower values indicate sharper peaks.

Number of lanes

Lane capacity (veh/h/ln)

Use your design standard or measured capacity.

Free-flow speed (km/h)

Baseline speed under low demand conditions.

Heavy vehicles (%)

Heavy-vehicle PCE

Higher values represent stronger truck impacts.

Segment length (km)

Used for context and reporting consistency.

Grade (%)

High grades can affect heavy vehicles.

Reset

Example data

Scenario	Volume (veh/h)	Lanes	Capacity (veh/h/ln)	PHF	HV (%)	PCE	FFS	Expected LOS
Urban bypass, moderate demand	3600	3	2000	0.92	6	2.0	105 km/h	C–D
Freight corridor, high trucks	4200	3	2000	0.90	18	2.5	95 km/h	D–E
Expansion check, added lane	4200	4	2000	0.92	10	2.0	105 km/h	B–C
Near-capacity peak hour	5200	3	2000	0.88	8	2.0	95 km/h	E–F

Examples show typical ranges; always confirm local standards and calibration data.

Formula used

Factored volume: Vf = V × demandFactor
Demand flow rate: v = Vf / PHF
Heavy vehicle adjustment (PCE method): vAdj = v × (1 + p × (PCE − 1)), where p = HV%/100
Per-lane flow: vPL = vAdj / lanes
Volume-to-capacity ratio: v/c = vPL / capPerLane
Estimated speed: S = FFS × (1 − 0.15 × (v/c)^4) (clamped to realistic bounds)
Density: D = vPL / S (veh per distance unit per lane)
LOS mapping (v/c): A≤0.60, B≤0.70, C≤0.80, D≤0.90, E≤1.00, F>1.00

How to use this calculator

Choose the facility type and the LOS basis you want to report.
Enter peak-hour volume, PHF, lanes, and lane capacity.
Add heavy-vehicle percentage and an appropriate PCE value.
Set free-flow speed and confirm units match your project notes.
Click Calculate to view LOS above the form.
Use Download CSV and Download PDF for reporting.
For final design, calibrate with local counts and accepted procedures.

Roadway service evaluation article

1) Why level of service matters on projects

Level of Service (LOS) is a practical way to summarize how well a roadway segment performs under a defined demand. Construction decisions like lane additions, median openings, and work-zone phasing can shift operations from stable flow to breakdown. A change from LOS C to LOS E typically signals that the segment is nearing capacity and will be sensitive to incidents, merges, and short-term surges.

2) Key inputs used in this calculator

The calculator combines peak-hour volume, peak hour factor (PHF), and a demand factor to estimate an adjusted demand flow. Lane capacity is entered per lane (veh/h/ln), then compared with the per-lane demand to obtain the v/c ratio. Free-flow speed is used to estimate operating speed and density for reporting and cross-checking.

3) Heavy vehicles and performance impacts

Trucks and buses consume more space and accelerate more slowly, especially on grades. The heavy-vehicle percentage and a passenger-car-equivalent (PCE) value convert mixed traffic into an equivalent flow. For example, 15% heavy vehicles with a PCE of 2.5 increases the equivalent demand by about 22.5%, often pushing v/c into a worse LOS band.

4) Typical thresholds and interpretation

In many planning checks, LOS A–C indicates stable operations, LOS D indicates limited comfort with rising delay, and LOS E represents near-capacity flow. Once v/c exceeds 1.00, LOS F is expected, with queues and spillback risk. For multilane facilities, density (veh/mi/ln) can provide an additional operational indicator.

5) How to use results in design and construction

Use the scenario table to compare alternatives: revise lane count, increase effective capacity, or reduce demand with staging and access management. Document assumptions (PHF, heavy vehicles, and free-flow speed) for review. Export CSV/PDF outputs to support traffic control plans, design narratives, and stakeholder approvals.

FAQs

1) What does v/c represent?

v/c is the per-lane demand flow divided by the per-lane capacity. Values below 1.00 typically indicate stable operations, while values above 1.00 indicate demand exceeds capacity and queues are likely.

2) How should I choose PHF?

Use a measured PHF from local counts when available. If not, typical planning values range from 0.85 to 0.95. Lower PHF values reflect stronger peaking and increase the calculated demand flow.

3) What PCE value is appropriate for heavy vehicles?

A common starting point is 2.0 for moderate conditions. Use higher values (2.5–3.0) where grades, frequent merges, or stop-and-go conditions increase truck impacts. Local guidance should govern final selection.

4) Why does the calculator estimate speed?

Speed is estimated from a simple speed–flow relationship to provide a consistent density estimate. It supports quick checks and reporting. For final analysis, calibrate with observed speeds and accepted modeling procedures.

5) When should I use density-based LOS?

Density-based LOS is most meaningful for freeway or multilane basic segments. It captures how closely vehicles are spaced per lane. Use it when your project reporting standard references density thresholds.

6) How do work zones affect inputs?

Work zones often reduce capacity and free-flow speed and may increase heavy-vehicle effects. Adjust lane capacity downward and revise free-flow speed based on the planned traffic control setup and expected driver behavior.

7) Can I use this for intersections?

This calculator is intended for roadway segments. Intersections typically use control delay and saturation flow methods. For intersection studies, use a dedicated intersection LOS approach consistent with your design manual.