Multilane Highway LOS Calculator

Automobile LOS on a four-lane highway with two lanes in each direction and uninterrupted flow. Choose HCM 2010 (Chapter 14), HCM 6th Edition (2016, Chapter 12), or compare both.

For a freeway with ramp access, use the basic freeway LOS calculator.

HCM edition

HCM 6th Edition combines all heavy vehicles and uses FFS directly.

View calculation formulas and LOS limits. Calculate LOS to see the formulas with your values substituted.

Traffic

Compare upgrade and downgrade conditions using the same directional demand. Enter the volume for one direction, across both lanes.

Directional hourly volume (veh/h)

Total heavy vehicles (%)

Include all trucks, buses and RVs. In this edition, buses and RVs count as single-unit trucks (SUTs).

Peak hour factor (PHF)

Terrain analysis

General terrain applies where no individual grade controls operations. Level terrain permits heavy vehicles to maintain passenger-car speeds; rolling terrain slows trucks without sustained crawl speeds.

Uniform grade

Uniform grade length (ft)

Grade magnitude (%)

HCM 6th Edition PCEs

Heavy-vehicle mix table

SUT = single-unit truck (including buses and RVs); TT = tractor-trailer. These percentages describe the heavy vehicles, not all traffic. The 30% SUT mix is more common on rural roads, 50% on urban roads; use 70% where SUTs predominate.

Automatic table lookup covers signed grades from -2% to +6%, lengths of at least 660 ft (0.125 mi), and at least 2% heavy vehicles. Longer grades use the last tabulated length; 25% and above use the final percentage column. Zero heavy vehicles needs no PCE adjustment.

Use a separately verified PCE

Use these optional overrides for conditions outside the tables or a documented local analysis. Each override replaces the automatic PCE for that direction.

Upgrade PCE override Downgrade PCE override Override basis / source

Free-flow-speed method

Measured speed Measured free-flow speed (mph)

Use a representative passenger-car speed study under low to moderate flow (up to 500 pc/h/ln for the 6th Edition). Roadway adjustments are already reflected in measured FFS.

FFS must be from 45 to 70 mph. HCM 6th Edition uses the measured or estimated speed directly, including intermediate values such as 56 mph.

Calculation formulas

Each direction uses N = 2 lanes. The formulas below follow your edition selection. Lateral-clearance and access adjustments are rounded to 0.1 mph. HCM 2010 also rounds interpolated PCEs to 0.1 and selects the nearest 5 mph speed curve.

1. Free-flow speed

Measured: FFS = measured free-flow speed
Estimated: FFS = BFFS - f_LW - f_TLC - f_M - f_A

BFFS is base free-flow speed. The deductions are for lane width (f_LW), total lateral clearance (f_TLC, called f_LC in HCM 2010), median type (f_M), and access-point density (f_A). All speeds and deductions are in mph.

Roadway adjustment formulas

TLC = min(right clearance, 6) + min(left clearance, 6)
f_A = 0.25 × min(access points per mile, 40)

TLC is in feet; use 6 ft on the left for an undivided highway or a two-way left-turn lane. Interpolate f_TLC from the lateral-clearance table. Round f_TLC and f_A to 0.1 mph.

For lane widths of at least 12 ft, f_LW = 0; from 11 to less than 12 ft, f_LW = 1.9; from 10 to less than 11 ft, f_LW = 6.6 mph. For an undivided highway, f_M = 1.6 mph; otherwise, f_M = 0.

HCM 6th Edition: heavy-vehicle adjustment and demand flow

Use the actual FFS from 45 to 70 mph, without rounding to a 5 mph curve.

P_T = heavy vehicles (%) / 100
f_HV = 1 / [1 + P_T(E_T - 1)]
v_p = V / (PHF × N × f_HV)

P_T is the heavy-vehicle fraction, E_T is the passenger-car equivalent (PCE), and f_HV is the heavy-vehicle adjustment factor. V is directional hourly volume (veh/h), PHF is peak hour factor, and v_p is passenger-car flow per lane (pc/h/ln).

PCE lookup and interpolation

Grade length (mi) = grade length (ft) / 5,280
y = y₁ + (y₂ - y₁) × (x - x₁) / (x₂ - x₁)

The interpolation equation finds y at x between two tabulated points (x₁, y₁) and (x₂, y₂). For a specific grade, apply it to heavy-vehicle percentage, then grade length, then signed grade in the selected SUT/TT table. Upgrade grade is positive; downgrade grade is negative. Lengths beyond the last row use that row; heavy-vehicle percentages of 25% and above use the final column.

General level terrain uses E_T = 2.0; rolling terrain uses E_T = 3.0. A documented PCE override replaces the table value. With no heavy vehicles, f_HV = 1.

3. Capacity

c = min[1,900 + 20 × (FFS - 45), 2,300]
Demand/capacity = v_p / c

c is capacity in pc/h/ln. If v_p > c, the result is LOS F; operating speed and density are not predicted.

4. Operating speed and density

For v_p ≤ 1,400: S = FFS
For 1,400 < v_p ≤ c:
S = FFS - (FFS - c / 45) × [(v_p - 1,400) / (c - 1,400)]^1.31
D = v_p / S

S is operating speed (mph), and D is density in passenger cars per mile per lane (pc/mi/ln).

5. Level of service

LOS limits for demand at or below capacity
LOS	Density D (pc/mi/ln)
A	0 ≤ D ≤ 11
B	11 < D ≤ 18
C	18 < D ≤ 26
D	26 < D ≤ 35
E	35 < D ≤ 45

Demand above capacity is LOS F. LOS is assigned using unrounded values.

HCM 2010: heavy-vehicle adjustment and demand flow

P_T = trucks and buses (%) / 100
P_R = RVs (%) / 100
f_HV = 1 / [1 + P_T(E_T - 1) + P_R(E_R - 1)]
v_p = V / (PHF × N × f_HV × f_p)

E_T and E_R are passenger-car equivalents for trucks/buses and RVs. V is directional volume (veh/h), PHF is peak hour factor, f_p is driver population factor, and v_p is flow in pc/h/ln.

Level terrain: E_T = 1.5, E_R = 1.2. Rolling terrain: E_T = 2.5, E_R = 2.0. Specific upgrades use Exhibits 14-13 and 14-14; downgrades use Exhibit 14-15 for trucks/buses and E_R = 1.2 for RVs.

Grade length (mi) = grade length (ft) / 5,280
E = E₁ + (E₂ - E₁) × (P - P₁) / (P₂ - P₁)

P is the vehicle-class percentage; P₁ and P₂ bracket it in the selected row, with equivalents E₁ and E₂. Round the interpolated E to 0.1. Grade and length select bands without interpolation; exact upper boundaries stay in the lower band (for example, 3% uses the >2–3% row).

HCM 2010: speed curve, capacity and density

FFS from 42.5 to less than 62.5 mph selects the nearest 5 mph curve, with ties rounding up. For example, 56 mph uses the 55 mph curve, while 57.5 mph uses the 60 mph curve. Use the selected speed F throughout the following calculation.

For v_p ≤ 1,400: S = F
For 1,400 < v_p ≤ c:
S = F - a × [(v_p - 1,400) / (c - 1,400)]^1.31
D = v_p / S
Demand/capacity = v_p / c

S is operating speed (mph), D is density (pc/mi/ln), c is capacity (pc/h/ln), and a is the speed-reduction coefficient from Exhibit 14-3.

HCM 2010 speed-curve parameters: F and a in mph; c in pc/h/ln; density in pc/mi/ln.
F	c	a	LOS E density limit
45	1,900	2.78	45
50	2,000	3.49	43
55	2,100	3.78	41
60	2,200	5.00	40

Density limits for LOS A, B, C and D are 11, 18, 26 and 35 pc/mi/ln. Above 35, flow at or below capacity is LOS E. Above capacity, the result is LOS F and speed/density are unavailable. The published rounded coefficients can put calculated density just above the tabulated E limit near capacity; the capacity test controls LOS F.

Method, sources and scope

Applies to uninterrupted automobile flow. Use a separate analysis for signal effects, queues from downstream bottlenecks, or composite grades. Run separately when traffic or FFS differs by direction. For steep grades or high truck percentages, HCM recommends its mixed-flow model for more detailed speed and density estimates.

Speed is reduced above 1,400 pc/h/ln. Demand above the selected curve's capacity is LOS F; speed and density are not predicted for that condition. Density is expressed in passenger cars per mile per lane (pc/mi/ln).

Basis: HCM 6th Edition, Volume 2, Chapter 12, Equations 12-1, 12-3, 12-7 and 12-9 through 12-11; Exhibits 12-6, 12-15, 12-20 and 12-22 through 12-28. Tables were checked against the supplied manual and ODOT Appendix 11D. See the source reconciliation and verification notes.

HCM 2010 basis: Chapter 14, Equations 14-1 through 14-5 and Exhibits 14-3, 14-4 and 14-8 through 14-15 (December 2010 printing). The 2010 implementation uses a separately verified transcription; the archived working pages are retained for history. See 2010 source verification, table limits and comparison notes. One disputed truck-table cell requires an override; later errata have not been verified.