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Nz Mugs Jon Slason 16 Oct2009


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Brief review of the uses of traffic models and compares a bit of US versus NZ usage.

Winner - Best Presentation of Conference.

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Nz Mugs Jon Slason 16 Oct2009

  1. 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 ( 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
  2. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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.
  12. 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. 13. Questions Jonathan Slason, PE p. 09-300-9063
  14. 14. 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.
  15. 15. 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.