10.3.4 Stage 2 Operational Performance and ICE

The main tools used in Stage 2 ICE are Synchro, HCS, and Vissim. The analysis software tool selection is based on intersection type, project complexity, and level of detail (see ). Information related to the capabilities of the software is found in
Chapter 4 and Chapter 12, Appendix M
.
When performing Stage 2 operational analysis, expanding the study area to include more than the project intersection is recommended if:
  • The study intersection or adjacent intersections will be impacted by queue spillback.
  • The study intersection operates within a coordinated system due to signalization.
  • The study intersection has geometric conditions in the vicinity, such as a nearby U-turn intersection.
See
Chapter 2
 for data collection resources.
provides needed and optional data inputs for the various tools in the two stages of ICE. For optional data inputs, default values are often used. Changing default values of optional data inputs is not critical to the analysis output but changing default values of needed data inputs is critical for operational analysis.

10.3.4.1 Service Volumes

FHWA has created “rule-of-thumb” intersection capacities that are used to determine if left-turn lane configuration at a signalized intersection is sufficient. See for thresholds based on various left-turn treatment scenarios.
Table 10-2: Operational Analysis Tools
Intersection Type
Level of Detail
Sketch Level or Macroscopic
HCM Based (Mesoscopic)
Microsimulation (Microscopic)
Two-Way Stop Control (TWSC)
Not applicable
Synchro, HCS
Vissim, CORSIM
All-Way Stop Control (AWSC)
Not applicable
Synchro, HCS
Vissim, CORSIM
Traffic Signal
CAP-X
Synchro, HCS
Vissim, CORSIM
Roundabout
See
Chapter 12, Appendix M
See
Chapter 12, Appendix M
See
Chapter 12, Appendix M
Alternative Intersection (DLT, RCUT, MUT, CGT, gradeseparated)
CAP-X
1
 (Synchro for CGT or grade separated)
Synchro, HCS2
Vissim, CORSIM
1
Synchro can be used for CGT and grade-separated intersections
2
Vissim can be used for HCM-based (mesoscopic) analysis when the facility type is unavailable in HCS
Table 10-3: Operational Analysis Tool Inputs (Stage 2 ICE)
Tool
Necessary Data Inputs
Optional Data Inputs
Synchro
  • geometric conditions
  • turning movement volumes (veh/hr)
  • speeds
  • peak hour factor
  • control type
  • heavy vehicle percentages
  • number of bus blockages
  • number of parking maneuvers
  • percent of traffic from midblock sources
HCS
  • geometric conditions
  • turning movement volumes (veh/hr)
  • speeds
  • peak hour factor
  • growth factor
  • control type
  • heavy vehicle percentages
  • buses/hour/approach
  • parking per hour
  • arrival type
  • detector length
  • initial queue
Vissim
  • geometric conditions
  • turning movement speeds
  • static vehicle routes (turning movement volumes veh/hr)
  • conflict rules
  • vehicle inputs
  • control type and signal timing
  • driver behavior parameters
  • heavy vehicle percentages
CORSIM
  • geometric conditions
  • turning movement volumes (veh/hr)
  • speeds
  • control type
  • heavy vehicle percentages
Table 10-4: Signalized Intersection Capacities for Exclusive Left Turn Treatments
Case I: No Exclusive Left-Turn Lanes
Assumed critical signal phases*
2
Left-turn volumes
Critical major approach**: ≤ 125 veh/hr
Critical minor approach: ≤ 100 veh/hr
Planning-level capacity (veh/hr), sum of critical approach volumes***
Number of basic lanes,**** major approach
2
3
4
Number of basic lanes, minor approach
1
1,700
2,300
-
2
2,400
3,000
-
3
-
-
-
Case II: Exclusive Left-Turn Lane on Major Approaches Only
Assumed critical signal phases
3
Left-turn volumes
Critical major approach: 150-350 veh/hr
Critical minor approach: ≤ 125 veh/hr
Planning-level capacity (veh/hr), sum of critical approach volumes
Number of basic lanes, major approach
2
3
4
Number of basic lanes, minor approach
1
1,600
2,100
2,300
2
2,100
2,600
2,800
3
2,700
3,000
3,200
Case III: Exclusive Left-Turn Lane on Both Major and Minor Approaches
Assumed critical signal phases
3
Left-turn volumes
Critical major approach: 150-350 veh/hr
Critical minor approach: ≤ 125 veh/hr
Planning-level capacity (veh/hr), sum of critical approach volumes
Number of basic lanes, major approach
2
3
4
Number of basic lanes, minor approach
1
1,500
1,800
2,000
2
1,900
2,100
2,400
3
2,200
2,300
2,800
Notes:
* Critical signal phases are nonconcurrent phases
**A critical approach is the higher of two opposing approaches (assumes same number of lanes)
***Use fraction of capacity for design purposes (e.g., 85 or 90 percent)
****Basic lanes are through lanes, exclusive of turning lanes
Adapted from NCHRP 279, figure 4-11

10.3.4.2 HCM-based

Synchro and HCS are recommended to be used when a more detailed analysis is necessary. HCM-based tools call for more inputs than CAP-X and sketch-level roundabout analysis and results could account for variables not considered with ICE Stage 1. For information on conducting an intersection analysis using HCM-based tools, refer to software user guides.

10.3.4.3 Microsimulation

Microsimulation may be used for intersection analysis where complex geometry exists, other tools cannot adequately model the intersection, and projects that call for high levels of detail. See
Chapter 13
 for more information on conducting an analysis using microsimulation.

10.3.4.4 Results and Measure of Effectiveness (MOEs)

Intersection analysis using HCM-based tools (i.e., Synchro and HCS) are evaluated in terms of LOS based on either control delay, LOS score (a measure used to rank pedestrian and bicycle facilities based on pedestrian perception and bicycle perception), or experienced travel time (ETT). shows the MOEs for each type of operational analysis tool. Enhanced operational performance equates to a low v/c ratio, low control delay, LOS A (optimal) to LOS D (acceptable), and short queue length.
The delay output by Vissim is calculated using a different method than in HCM based tools, so use caution when comparing the delays between Vissim results and HCM-based software. Relevant pairs of intersection chapters from the HCM 7th Edition are listed below:
  • Signalized Intersections: Chapter 19 (methodology), Chapter 31 (applications);
  • Two-way Stop-controlled Intersections: Chapter 20 (methodology), Chapter 32 (applications);
  • AWSC: Chapter 21 (methodology), Chapter 32 (applications);
  • Roundabouts: Chapter 22 (methodology), Chapter 33 (applications); and
  • Alternative Intersections (Continuous Flow/Displaced Left-Turn, RCUT, MUT): Chapter 23 (methodology), Chapter 34 (applications)
shows HCM LOS criteria for signalized intersections. provides HCM LOS criteria for TWSC and AWSC intersections.
Table 10-5: Operational Analysis Tool Outputs
Tool
Outputs
CAP-X
v/c ratios of top 10 selected intersection types
Synchro
v/c ratio, control delay, LOS, 95% queue length
HCS
v/c ratio, control delay, LOS, 95% queue length,
Warrants (using Synchro, HCS, or other tools)
Warrant met or warrant not met
Vissim
Average vehicle travel times (sec), average total delay per vehicle (sec), percent of queue length, ETT
CORSIM
Control delay, queue length, travel speed, travel time, LOS
Table 10-6: LOS Criteria for Signalized Intersections: Motorized Vehicle Mode
Control Delay
(s/veh)
LOS by Volume-to-Capacity Ratioa
v/c ≤ 1.0
v/c >1.0
≤ 10
A
F
> 10-20
B
F
> 20-35
C
F
> 35-55
D
F
> 55-80
E
F
>80
F
F
Note: For approach-based and intersection-wide assessments, LOS is defined solely by control delay.
Table 10-7: LOS Criteria for TWSC & AWSC Intersections: Motorized Vehicle Mode
Control Delay
(s/veh)
LOS by Volume-to-Capacity Ratio
v/c ≤ 1.0
v/c >1.0
≤ 10
A
F
> 10-15
B
F
> 15-25
C
F
> 25-35
D
F
> 35-50
E
F
>50
F
F
Note: The LOS criteria apply to each lane on a given approach and to each approach on the minor street. LOS is not calculated for major-street approaches or for the intersection.