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