Traffic Flow / LOS Calculator
Calculate level of service (LOS) for highways based on HCM methodology. Computes flow rate, density, v/c ratio, and LOS grade for freeways, multilane, and two-lane highways.
Engineering Formulas
Adjusted Flow Rate
Heavy Vehicle Factor
Density
Level of Service (Freeway)
Worked Example
Freeway LOS Analysis
Engineering Notes
Assumptions
Common Mistakes
Frequently Asked Questions
What is Level of Service (LOS)?
LOS grades traffic conditions from A (free flow) to F (congested/breakdown). It is based on density (pc/km/lane) for freeways and multilane highways per HCM methodology.
What is Peak Hour Factor (PHF)?
PHF = (peak hour volume) / (4 × peak 15-min flow rate). Values range 0.75–0.95. Lower PHF means more peaking within the hour, reducing effective capacity.
What is the heavy vehicle factor?
fhv accounts for the space occupied by trucks and RVs which are larger and have poorer performance than passenger cars. It reduces the effective flow rate capacity.
What is free flow speed?
FFS is the average speed at low volumes (typically 100–120 km/h for freeways). It depends on speed limit, lane width, lateral clearance, and interchange density.
What is the v/c ratio?
v/c ratio compares actual flow rate to capacity. v/c < 0.7 indicates good conditions, 0.7–0.9 approaches congestion, > 0.9 indicates near-breakdown conditions.
How does terrain affect capacity?
Trucks slow more on upgrades in rolling/mountainous terrain, reducing capacity. E_T = 1.5 (level), 2.5 (rolling), 4.5 (mountainous) per HCM.
What is a typical freeway capacity?
HCM recommends 2,200–2,400 pc/h/ln for freeways with FFS ≥ 100 km/h. Capacity decreases with lower FFS (≈2,100 at 80 km/h).
What is LOS F?
LOS F represents breakdown flow with stop-and-go conditions. Density exceeds 28 pc/km/lane for freeways. Demand exceeds capacity, causing queue formation.