Highway Capacity Flow Rate

What is this formula?

The Highway Capacity Flow Rate equation converts observed traffic volume into an equivalent passenger-car flow rate used in highway capacity analysis.

This adjustment accounts for peak-hour traffic concentration, heavy vehicles, and driver population characteristics.

The resulting value is one of the key inputs in Highway Capacity Manual (HCM) methodologies.

When to use it

Use this formula when analyzing:

- Highway capacity

- Level of Service (LOS)

- Freeway operations

- Multilane highways

- Traffic engineering studies

Example

A highway segment has:

V = 4200 veh/h

PHF = 0.92

N = 3

fHV = 0.95

fp = 1.00

Formula:

vp = V/(PHF·N·fHV·fp)

Substitution:

vp = 4200/(0.92×3×0.95×1.00)

vp = 1602 pc/h/ln

Result:

vp ≈ 1602 pc/h/ln

Applications

- Capacity analysis

- Level of Service evaluation

- Traffic impact studies

- Highway design

- Transportation planning

Note

This equation follows the general structure used in the Highway Capacity Manual. Actual capacity analysis may include additional adjustment factors depending on roadway type, terrain, lane width, interchange density, and local traffic characteristics.