Freeway Merge and Diverge Segments

The compute engine reproduces the published HCM worked examples for this chapter under both editions. The 7th Edition and Edition 7.1 are different models. The same junction can land a full LOS letter apart between them, and under 7.1 a density above 35 pc/mi/ln is LOS F on its own where Exhibit 14-3 read it as LOS E, so results are only comparable within one edition. Please report discrepancies on GitHub.

Configuration

Junction type and geometry of the ramp-freeway junction.

HCM Edition

Edition 7.1 replaces this chapter's methodology; the editions report different speeds, capacities, and LOS.

Ramp Type

Ramp Side

Ramp Lanes

Freeway Lanes (one direction)

Acceleration Lane Length (L_A)

Used for on-ramps and major merges.

Deceleration Lane Length (L_D)

Used for off-ramps and major diverges.

Terrain

Hover the legend to highlight the ramp or the influence area the method evaluates. The picture follows the inputs.

L_A ft

Traffic

Freeway and ramp demand and traffic-stream characteristics.

Freeway Demand

veh/h

Demand immediately upstream of the junction.

Ramp Demand

veh/h

Freeway Free-Flow Speed

mph

Ramp Free-Flow Speed

mph

Peak Hour Factor

Heavy Vehicles (Freeway)

Heavy Vehicles (Ramp)

Capacity Adjustment Factor

Use 1.00 for base conditions.

Speed Adjustment Factor

Use 1.00 for base conditions.

Outputs

Results populate after pressing Calculate.

Freeway Flow Rate (pc/hr):
Ramp Flow Rate (pc/hr):
Flow in Lanes 1 and 2 (pc/hr):
Freeway Capacity (pc/hr):
Ramp Capacity (pc/hr):
Volume-to-Capacity Ratio:
Demand Exceeds Capacity:
Ramp Influence Area Density (pc/mi/ln):
Ramp Influence Area Speed (mi/hr):
Average Speed, All Lanes (mi/hr):

Segment LOS: