HCM Chapter 12

Basic Managed Lane Segments

Estimate capacity, space mean speed, density, and level of service for a basic managed lane segment adjacent to general purpose freeway lanes.

Scope. The compute engine is boundary-validated against HCM Chapter 26, Example Problem 7 (both cases), which the page defaults reproduce, and against the Exhibit 12-30 separation parameters and the Exhibit 12-11 capacities at every tabulated free-flow speed. The page itself is in beta pending final inspection. Verify results independently before relying on them in engineering work, and please report discrepancies on GitHub.

Managed Lane

Separation from the general purpose lanes, free-flow speed, and the two adjustment factors.

Exhibit 12-30 defines a separate speed-flow calibration for each of the five types.

mi/h

The selected Exhibit 12-30 row describes a single-lane facility.

Use 1.00 for base conditions. Equation 12-14 is linear in CAF, Equation 12-13 squares it.

Use 1.00 for base conditions. Applies to the free-flow speed before the breakpoint and capacity are computed.

Plan view. The managed lanes are the left-most lanes of the roadway, so they are drawn above the general purpose lanes. The managed lane is tinted by its level of service after a run.

Traffic

Hourly demand in the analysis direction. Equation 12-9 converts it to a per-lane flow rate in passenger cars.

veh/h
%

Applied to both carriageways, as in Example Problem 7.

Exhibit 12-25 general terrain. Mountainous terrain requires the Chapter 25 mixed-flow model and is not offered here.

Adjacent General Purpose Lanes

The GP lanes are analyzed as a basic freeway segment. Their density drives the friction term of Equation 12-18, which applies to continuous access and Buffer 1 separations above 35 pc/mi/ln.

veh/h

Example Problem 7 runs 2,000 veh/h as Case 1 and 3,800 veh/h as Case 2.

mi/h
pc/h/ln

From the Chapter 12 basic-segment analysis of the adjacent lanes.

pc/h/ln

Outputs

Results populate after pressing Calculate.

Heavy-Vehicle Factor, fHV:
Managed Lane Flow Rate (pc/h/ln):
GP Flow Rate (pc/h/ln):
GP Speed (mi/h):
GP Density, KGP (pc/mi/ln):
Speed-Flow Breakpoint (pc/h/ln):
Adjusted Capacity (pc/h/ln):
Space Mean Speed (mi/h):
Density (pc/mi/ln):
GP Lane Friction Active:

Segment LOS: