Guide for Highway Capacity and Operations Analysis of Active Transportation and Demand Management Strategies
Appendix H: Speed/Capacity for Shoulder/Median Lane Strategies
This Appendix provides details on the free-flow speed and capacity adjustments associated with the temporary shoulder and median lane strategies.
Open Shoulders As Auxiliary Lanes Between Adjacent On- and Off-Ramps
This strategy involves opening a shoulder lane for use by all vehicles entering at the upstream on-ramp or exiting at the downstream off-ramp. Some through vehicles may temporarily use the auxiliary lane to try and jump ahead of the queue.
The capacity of an auxiliary lane is assumed by the HCM 2010 freeway method to be the same as a regular lane, however; actual utilization of the auxiliary lane may be quite a bit lower than for a through lane. In addition, the HCM 2010 freeway method does not provide a capacity for shoulder lanes. Until such time as the HCM has specific information on the capacities of auxiliary shoulder lanes, this procedure assumes that the capacity of an auxiliary shoulder lane is one-half that of a normal freeway through lane (1,050 vph) (user can override this value in cell X26 of the “30 Lanes” worksheet).
Since, the HCM 2010 freeway method does not recognize individual lane capacities, it is necessary to compute an average capacity for freeway sections with auxiliary shoulder lanes, across all lanes.
Where:
AveCap(s) = average capacity per lane for section(s) (vph/ln)
CapShldr(s) = capacity per shoulder lane (vph/ln) (assume only one shoulder lane)
CapMFLanes = capacity per mixed-flow lane (vph/ln).
MFLanes(s) = Number of mixed-flow lanes in section(s)
The number of lanes on the freeway segments between adjacent on- and off-ramps is increased by one for the shoulder lane.
Until such time as the HCM has more specific information for shoulder lanes, free-flow speeds on auxiliary shoulder lanes are assumed in this procedure to be the same as for regular through lanes.
Open Shoulders To Buses Only
This strategy involves opening a shoulder lane to buses only. The same procedure and assumptions as described above for auxiliary shoulder lanes is used to compute freeway section capacities, lanes, and free-flow speeds where buses are allowed on shoulders, with the following exceptions:
- Capacity of the shoulder lane is the number of buses per hour using the shoulder lane or the user specified capacity, whichever is less (user can override the default capacity).
Open Shoulders To HOVs Only
This strategy involves opening a shoulder lane to buses, vanpools, and carpools (HOVs) only. The same procedure and assumptions as described above for auxiliary shoulder lanes is used to compute freeway section capacities, lanes, and free-flow speeds where HOVs are allowed on shoulders, with the following exceptions:
- Capacity of the shoulder lane is the number of HOVs per hour using the shoulder lane or the user specified capacity, whichever is less.
Open Shoulders To All Traffic
This strategy involves opening a shoulder lane to all vehicles.
The same procedure and assumptions as described above for auxiliary shoulder lanes is used to compute freeway section capacities, lanes, and free-flow speeds where all vehicles are allowed on shoulders, with the following exceptions:
- Capacity of the shoulder lane is as specified by the user.
Open Median To Buses Only
This strategy involves opening a median lane to buses only. The same procedure and assumptions as described above for auxiliary shoulder lanes is used to compute freeway section capacities, lanes, and free-flow speeds, with the following exceptions:
- Capacity of the median lane is the number of buses per hour using the shoulder lane or the user designated capacity, whichever is less.
Open Median To HOVs Only
This strategy involves opening a median lane to HOVs (buses, vanpools, carpools) only. The same procedure and assumptions as described above for auxiliary shoulder lanes is used to compute freeway section capacities, lanes, and free-flow speeds, with the following exceptions:
- Capacity of the median lane is the number of HOVs per hour using the shoulder lane or the user designated capacity, whichever is less.
Open Median To All Traffic
This strategy involves opening a median lane to all traffic. The same procedure and assumptions as described above for auxiliary shoulder lanes is used to compute freeway section capacities, lanes, and free-flow speeds, with the following exceptions:
- Capacity of the median lane is as designated by the user.
