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Transportation Research BoardPlanning Applications Conference, May 2007
Given by:
Ronald T. Milam, AICP
Contributing Analysts:
David Stanek, PE
Chris Breiland
Mike Iswalt
The Secrets to HCM Consistency Using Simulation Models
Typical Simulation Examples
When to Use Simulation
When to Use Simulation
When vs. How?
The HCM methodologies may not be appropriate in environments with multiple travel modes or multiple hours of congestion.
“… the HCM methods are generally not appropriate…for the evaluation of queues that are building over both time and space.” – Page 9-1, HCM 2000
“ Certain freeway traffic conditions cannot easily be analyzed by the methodology. Multiple overlapping bottlenecks are an example. Therefore, other tools may be more appropriate…” - Page 22-1, HCM 2000
Challenges/Issues
Multiple software packages• AIMSUN• CORSIM• Dynasim• Paramics• SimTraffic• TransModeler• VISSIM• others…
Which ones are HCM consistent?
How can a user or reviewer be sure?
Traffic simulation programs provide many performance measures
• Total delay• Density• Travel time• Average speed• Travel distance• Number of stops
However, the definition of the performance measures may differ from the HCM definition.
• Stopped delay• Throughput• Emissions• Fuel consumption• Queue length• Others
Simulation Performance Measures
HCM Performance Measures
HCM methods determine LOS for facility types based on different performance measures
Facility Type• Intersections• Urban Streets• Two-Lane Highways
• Multi-lane Highways• Freeways
Performance Measure• Control Delay• Speed• Percent Time
Spent Following
• Density• Density
Roadway System• Peak hour factor
Intersections• Defining the intersection approach
Freeways• Ramp influence areas
Consistency Issues
Peak Hour Factor
HCM defines the LOS for the peak 15 minutes of the peak hour
800
850
900
950
1000
1050
1100
Flo
w (
vp
h)
4:15PM
4:30PM
4:45PM
5:00PM
5:15PM
5:30PM
Peak HourPeak HourPeak 15-Minute Peak 15-Minute VolumeVolume
Peak Hour Peak Hour VolumeVolume
Edit the periods file to create 15-minute interval demand periods.
Peak Hour Factor, continued…
Paramics Example
Use the divisor parameter in the demands file to adjust peak hour volumes. Hourly data with PHF of 0.95 implies a divisor of 3.8.
Peak Hour Factor, continued…
Paramics Example
Include delay for all vehicles on approach
• Model link delay may not include entire intersection approach
Model Network
Maximum Queue
Intersection Approach Delay
Intersection Approach Delay, continued…
SimTraffic Example
Upstream unsignalized intersection divides the southbound approach into two links.
Upstream unsignalized intersection divides the southbound approach into two links.
Intersection Approach Delay, continued…
Unsignalized Driveway Intersection
Signalized Intersection
Link 1
Link 2
SimTraffic Example
SimTraffic Example
Output report for signalized intersection shows delay for Link 1 only.
Intersection Approach Delay, continued…
SimTraffic Example
Adding delay for Links 1 and 2 to get the entire southbound approach delay.
LOS Results Link 1 Links 1 & 2
SB Approach E / 59 F / 86
Intersection D / 40 D / 44
Intersection Approach Delay, continued…
HCM defines the ramp merge analysis area as the two right shoulder lanes plus the auxiliary lane for 1,500 feet downstream of the ramp gore
Ramp influence area does not necessarily match model links
Ramp Influence Area
Build model network to account for ramp influence area and volume collection locations.
Ramp Influence Area, continued…
VISSIM Example
VISSIM Example
Ramp merge area with acceleration lane
450 ft450 ft
Ramp Influence Area
Ramp Influence Area
Ramp Influence Area, continued…
Link 190
Link 191
2,930 ft2,930 ft
On-Ramp
Collect statistics for ramp influence area.
450 ft450 ft
1,050 ft1,050 ft
Ramp Influence Area, continued…
VISSIM Example
Collect statistics by lane for each link.
Ramp Influence Area, continued…
VISSIM Example
Calculate volume-weighted average density first across links, then across lanes
Ramp Influence Area, continued…
Across LinksAcross Links
Across LanesAcross Lanes
VISSIM Example
Analysis Results
Location Density (vpmpl) LOS
Link 190 (all lanes) 42.4 E
Link 191 (all lanes) 37.2 D
Ramp Influence Area 42.1 E
Ramp Influence Area
Ramp Influence Area
Ramp Influence Area, continued…
VISSIM Example
Link 190
Link 191
• FHWA - Modify NGSIM priorities to better reflect user needs
• TRB - Update the HCM to provide specific guidelines for simulation software vendors and to reflect a wider range of performance measures
• Software Vendors – Provide technical support and training on HOW to perform simulation modeling
• Users – Invest time to understand HOW to perform simulation modeling
Recommendations
Questions?
The Secrets to HCM Consistency Using Simulation Models