This document presents a detailed exploration of planning and transportation engineering modeling in the U.S., focusing on the development, use, and challenges of various modeling approaches, including deterministic and microsimulation models. It discusses the changing demands on traffic models due to increasing congestion, environmental concerns, and sophisticated intersection controls, while highlighting the importance and limitations of Level of Service (LOS) as a measure of transportation quality. Furthermore, it introduces Transims, an advanced modeling system for travel demand and behavior analysis, contrasting it with traditional 4-step models.

1. Concepts of Planning and
Transportation Engineering from a
modelling perspective in the US
Presentation made to the NZ Model Users
Jonathan Slason, PE Group Conference
Transportation Engineer at Beca (www.beca.com) 15 October 2009
The views expressed are those of the author and do not necessarily reflect those of Beca or any other organisation or
agency.
Jonathan Slason, PE
Further detail behind the issues raised is Engineer, Beca
Transportation available by contacting jonathan.slason@beca.com

2. Reasons for Modelling
- Planning: Statewide, Regional, City, project specific
-Consent: Resource consent processes (NEPA), state or city
specific impact assessment processes
-Operations: design flows, operational assessments,
optimisation
Source: Traffic Analysis Toolbox Volume I:Traffic Analysis Tools Primer
PUBLICATION NO. FHWA-HRT-04-038 JULY 2004

3. Planning
Changing demands on models.
- Increasing sophistication of intersection control types
- Increasing congestion
- Increasing appreciation of mode choice
- Mix of land use types creating less homogenous land types
- Environmental: GHG, Noise, Particulates, Stormwater

4. Consent
Rigorous review of Models
-Often deterministic models are sufficient. HCM Methodology
-Varies by jurisdiction on level of analysis
-Concurrency vs. Infill and Urban Planning concepts
KPI’s & MOE’s
-Level of Service (avg. Vehicle delay)
-Volume to Capacity
-95 percentile queues
Most Jurisdictions have a Level of Service policy or Concurrency Policy
with rules on allowable degree of impact or effect on future operations.
LOS is clearly the most often used MOE in the US.
In the End - LOS is simply a quantitative representation of
transportation users’ perspectives of transportation Quality
of Service.

5. Consent
Consent
Microsimulation and Deterministic Models often used together
to provide HCM outputs, volume to capacity, and queuing
details.
HCM Limitations on Methodology support the use of
Microsimulation to assess operations
Common Limitations:
-Closely spaced intersections
-Congested areas
Oregon, USA -
“…A queue blockage or spillback condition is considered a
problem when the duration exceeds 5 percent of the peak
hour. “

6. Consent
Consent
Examples of consent rules
Los Angeles Polly
Caltrans endeavors to maintain a
target LOS at the transition
between LOS “C” and LOS “D”
Approximately 1/3 of the states
in the US aim for a LOS “C” for
target operations.
The remaining prefer to NOT
state their objective and leave it
up to specific cities or a pre-
San Diego Policy
arranged negotiation of ‘impact’.

7. Consent Trends
Florida analysis zones
NOT a one size fits
all analysis.
Early
appreciation
that different
urban areas
have different
expectations. Florida TIS/LOS guidebook - 2002

8. Operations
More demands
- Increasing sophistication of intersection control types. Multi-
modes, buses, cycles, pedestrians, pre-emption, etc.
- Detailed interaction and effects of downstream/upstream
capacities
-Desire for Signal Timing and very detailed operational
enhancements to come from models
Multiple Ring (most often Dual Ring), multiple barrier signals are default in the
US. SCATS used here in NZ provides different adaptive signal setup. SCATS can
be modelled in most software with a correct dual ring setup.
Most analysis software was initially setup to model the US style of signals.
ScatsSim operates with the
following
Micro-simulation packages :
• Paramics (S & Q)
• Aimsun (TSS)
• Vissim (PTV)

9. Current Behaviour
Most often used analysis software in use in the US
Deterministic:
HCM Analysis conducted by Synchro and HCS+
Microsimulation:
SimTraffic
Paramics (Q)
Vissim

10. What’s the Difference?
- Review of Models performed by government agencies.
-Government has skills and responsibility to accept
results. When they don’t they retain consultants who can
review on their behalf.
- peer review process not commonly used
-Litigious environment changes when and how models are
used
-Defensible (standard practice, guidelines)
-Often results in another model being built to justify the
first one
-Negotiation/arbitration in the end
NEPA and other environmental review procedures allow a
variety of stakeholders to challenge, review, and produce
alternative models.

11. Trends
Demand for models have increased with improved access to
faster computers, more focused applications, and increasing
educational focus from Universities.
Results
-Micro for Specific Purposes
-Discrete Choice Macro Models
Departure from the 4-Step Process
TRANSIMS
TRansportation ANalysis and SIMulation
System (TRANSIMS).
TRANSIMS is the next generation of travel
modeling, microsimulation and air quality
analysis tools.
http://tmip.fhwa.dot.gov/resources/clearinghouse/docs/transims_fundamentals/

12. Two Trends
Macro Trends
The Discrete processes require advanced mixed nested
logit models for modelling the hierarchy of trip choices
and modal options.
Required computing power is substantial with some new
models requiring 24 hours to run through.
Micro Trends
Over reliance on micro models have made some
jurisdictions revert back to simple first principles and
general planning. The answers provided by the modelling
rarely justifying the cost and complexity.
Focus on the core benefits of Micro modelling

13. Questions
Jonathan Slason, PE
Jonathan.slason@beca.com
p. 09-300-9063

15. How TRANSIMS Compares to 4-Step Models
Different From 4-Step Models Similar to 4-Step Models
Framework The microsimulation and travel behavior sub models in TRANSIMS provides a collection of software modules and utilities to build models of
TRANSIMS share data easily. Model iteration works with travel demand and transport networks.
individual travelers rather than aggregate demand data. Time
is a continuous variable throughout the framework.
Travel TRANSIMS models and tracks travel for each individual and TRANSIMS may estimate demand from a zonal rate-based model.
demand vehicle. The TRANSIMS activity model uses a statistical
generation sampling method to draw an activity pattern for a modeled
household from a demographically similar survey household.
Destination Destination choice for each trip is made for each traveler Zonal interchanges can be estimated with a user defined gravity model. Choice of
choice rather than aggregate trips by purpose by zone. intermediate destinations on a tour may also be estimated.
Mode choice TRANSIMS applies a user defined mode preference for each Modes are user defined. The mode preference model structure is user defined.
traveler. All travel starts and ends with a walk segment and Applications to date use zone-zone auto and transit impedance with terminal
transfers are explicitly routed as walks. For a given trip, the characteristics as preference variables. The Router makes the final walk vs. vehicle
TRANSIMS Router may find that walking is a better choice choice. Walking, bicycling, SOV, auto passenger, transit bus, school bus, fixed
than a vehicle and use walk for that particular trip. guideway transit, and park-and-ride have been modeled to date.
Route choice TRANSIMS uses a routing network representing all available TRANSIMS finds the shortest time path between two points on a network. Cost
and transport services with facility service quality aggregated to variables can be incorporated using a value of time for each traveler. All-or-nothing,
simulation fifteen-minute intervals. Path finding is link based. The Router iterative capacity-restrained, and (Nash) equilibrium assignment methods can be
relies on the Microsimulator to provide expected link travel replicated.
times. The Microsimulator is an integral part of the TRANSIMS
tool set.

16. How TRANSIMS Compares to 4-Step Models
Different From 4-Step Models Similar to 4-Step Models
Time Traveler itineraries and subsequent vehicle uses are Trip time of departure can be estimated using diurnal factors. Results can
scheduled according to a travel survey and refined based be aggregated to the hour, period or entire day.
on simulation results. Demand is estimated to the minute
and simulated to the second.
Data Networks Networks
Stop signs, traffic signalization, and intersection lane A link-node format is used to describe topology. Existing network data or a
geometries need to be coded. Land Use, Population and commercial GIS dataset can provide the basis for an initial highway
Employment data network. Existing headway and route data may be used to generate initial
TRANSIMS generates trip-end locations automatically, transit files, schedules and run details. The network database needs to be
they must be refined manually. appropriately corrected and calibrated. Land Use, Population and
Monitoring and Surveys Employment data
In addition to other data TRANSIMS reads 15-minute Existing zone and parcel data may be allocated to activity locations. Census
ATR/ATC/ITS data. data, including SF3 and PUMS data are key elements for population
synthesis, augmented by demographic forecasts for future years.
Monitoring and Surveys
Household activity survey
External stations counts, forecast, intercept survey
Transit on-board surveys
Traffic count databases
Computing A Linux server or Linux cluster is used for model Model results are analyzed using Windows or Unix workstations.
Environment application. The framework is scalable to allow more
computers to be used on larger, more complex problems.