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HPMS Field Manual

Appendix N: Procedures for Estimating Highway Capacity

Rural One-Lane Capacity

Application

These highways, though rare, do exist in HPMS. They include facilities with both one-way and two-way operation.

Procedure

One-Way Operation

The capacity of these sections should be computed using the procedure for Rural Two-Lane Highways, with the following changes:

• Change the base capacity from 3,200 pch to 1,600 pch
  
  
• Compute the one-way flow rate using the same equation as for two-way flow rate; enter all lookup tables and equations labeled for two-way flow rate with this value.
  
  
• Assume 100% no passing zones.

The resulting capacity is, by definition, a one-way value.

Two-Way Operation

One-lane highways open to both directions of traffic are extremely rare. For these cases, compute the capacity for one-way operation and divide by 2.

Rural Three-Lane Highway Capacity

Application

These highways have two through lanes in one direction and a single lane in the opposite direction. The through lanes are assumed to cover an extended length and are not auxiliary or truck climbing lanes. (This is consistent with the coding of HPMS data).

Procedure

It is assumed that these highways operate as a multilane undivided facility in the two-lane direction and as a single direction of a rural two-lane facility in the one-lane direction. The two-way capacity (required by HPMS for these facilities) is then the sum of these two separate capacities.

The capacity for the two-lane direction is computed using the Multilane Highway capacity procedure assuming an undivided cross-section. The capacity for the one-lane direction is computed using the procedure for Rural One-Lane, One-Way Highways.