Appendix B - Impacts Analysis Tools

Several methodologies and tools are available for conducting transportation analyses and estimating the effects of various transportation planning alternatives and projects. These tools vary in level of complexity, and each tool offers different capabilities. Some tools were designed specifically for work zone applications. Other traffic analysis tools, although not designed specifically for work zones, can be used for to analyze work zone situations. This section includes information on both of these types of tools.

Types of Traffic Analysis Tools

Traffic analysis tools can be grouped into the following categories:

• Sketch-planning tools – Sketch-planning methodologies and tools produce general order-of-magnitude estimates of travel demand and traffic operations in response to transportation improvements. They allow for evaluation of specific projects or alternatives without conducting an in-depth engineering analysis. Sketch-planning tools perform some or all of the functions of other analysis tool types using simplified analyses techniques and highly aggregate data. Such techniques are primarily used to prepare preliminary materials and budgets, and are not considered a substitute for the detailed engineering analysis often needed later in the project design and implementation process. Sketch-planning approaches are typically the simplest and least costly of traffic analysis techniques, and are usually limited in scope, analytical robustness, and presentation capabilities. Examples of sketch-planning tools include QuickZone, Surface Transportation Efficiency Analysis Model (STEAM), and ITS Deployment Analysis System (IDAS). QuickZone was developed for work zone applications and is described in the Work Zone Specific Analysis Tools section later in this appendix.
• Travel demand models – Travel demand models have specific analytical capabilities, such as the prediction of travel demand and the consideration of destination choice, mode choice, time-of-day travel choice, and route choice, as well as the representation of traffic flow in the highway network. These are mathematical models that forecast future travel demand based on current conditions, and future projections of household and employment characteristics. Travel demand models were originally developed to determine the benefits and impacts of major highway improvements in metropolitan areas. Travel demand models are suited for static analyses and are not capable of dynamic traffic analysis (i.e., time-varying analyses). Therefore, they have only limited capabilities to evaluate ITS/operational strategies and operational characteristics such as speed, delay, and queuing. Examples of travel demand models include TransCAD, Cube, Quick Response System (QRS) model, Équilibre Multimodal, Multimodal Equilibrium 2 (EMME2), IDAS[1], and VISUM.
• Analytical/deterministic tools (HCM Based) – Most analytical/deterministic tools implement the procedures of the Highway Capacity Manual (HCM). HCM procedures are closed-form, macroscopic, deterministic, and static analytical procedures that estimate capacity and performance measures to determine the level of service (e.g., density, speed, and delay). They are closed-form because they are not iterative. The practitioner inputs the data and parameters and, after a sequence of analytical steps, the HCM procedures produce a single answer. Moreover, HCM procedures are macroscopic (inputs and outputs deal with average performance during a 15-minute or a one-hour analysis period), deterministic (any given set of inputs will always yield the same answer), and static (they predict average operating conditions over a fixed time period and do not deal with transitions in operations from one state to another). As such, these tools quickly predict capacity, density, speed, delay, and queuing on a variety of transportation facilities and are validated with field data, laboratory test beds, or small-scale experiments. Analytical/deterministic tools are good for analyzing the performance of isolated or small-scale transportation facilities, but are limited in their ability to analyze network or system effects. Examples of analytical/deterministic tools include Highway Capacity Software (HCS), Synchro, and the TEAPAC suite of programs.
• Traffic signal optimization tools – Traffic signal optimization tools are similar to analytical/deterministic tools, and are largely based on HCM procedures. However, traffic signal optimization tools are primarily designed to develop optimal signal phasings and timing plans for isolated signal intersections, arterial streets, or signal networks. Some optimization tools can also be used for optimizing ramp metering rates for freeway ramp control. The more advanced traffic signal optimization tools are capable of modeling actuated and semi-actuated traffic signals, with or without signal coordination. Examples of traffic signal optimization tools include Progression Analysis and Signal System Evaluation Routine (PASSER), Signal Operations Analysis Package (SOAP), Synchro, Traffic Network Study Tool (TRANSYT-7F), Time-Space Diagram for Windows (TSDWin), and the TEAPAC suite of programs.
• Macroscopic simulation models – Macroscopic simulation models are based on deterministic relationships of flow, speed, and density of the traffic stream. The simulation in a macroscopic model takes place on a section-by-section basis rather than tracking individual vehicles. Macroscopic simulation models were originally developed to model traffic in distinct transportation subnetworks, such as freeways, corridors (including freeways and parallel arterials), surface street grid networks, and rural highways. They consider platoons of vehicles and simulate traffic flow in small time increments. Macroscopic simulation models operate on the basis of aggregate speed/volume and demand/capacity relationships. Macroscopic models have considerably less demanding computer requirements than microscopic models. They do not, however, have the ability to analyze transportation improvements in as much detail as microscopic models, and do not consider trip generation, trip distribution, and mode choice in their evaluation of changes in transportation systems. Examples of macroscopic simulation models include Bottleneck Traffic Simulator (BTS), Freeway Corridor Simulation Model (FREQ), Corridor Flow Simulation Software (CORFLO), PASSER, and TRANSYT-7F.
• Mesoscopic simulation models – Mesoscopic models combine properties of both microscopic (discussed below) and macroscopic simulation models. As in microscopic models, the mesoscopic models' unit of traffic flow is the individual vehicle. Similar to microscopic simulation models, mesoscopic tools assign vehicle types and driver behavior, as well as their relationships with the roadway characteristics. Their movement, however, follows the approach of macroscopic models and is governed by the average speed on the travel link. Mesoscopic model travel prediction takes place at an aggregate level, and does not consider dynamic speed/volume relationships. As such, mesoscopic models provide less accuracy than microsimulation tools, but are superior to typical planning analysis techniques. Examples of mesoscopic models include Continuous Traffic Assignment Model (CONTRAM), and Dynamic Network Assignment Simulation Model for Advanced Road Telematics for Planning (DYNASMART-P).
• Microscopic simulation models – Microscopic simulation models simulate the movement of individual vehicles, based on theories of car-following and lane-changing. Typically, vehicles enter a transportation network using a statistical distribution of arrivals (a stochastic process), and are tracked through the network over small time intervals (e.g., one second or fraction of a second). Typically, upon entry, each vehicle is assigned a destination, a vehicle type, and a driver type. In many microscopic simulation models, the traffic operational characteristics of each vehicle are influenced by vertical grade, horizontal curvature, and super-elevation, based on relationships developed in prior research. Computer time and storage requirements for microscopic models are large, usually limiting the network size and the number of simulation runs that can be completed. Examples of microscopic simulation models include Traffic Software Integrated System/Corridor Simulation (TSIS/CORSIM), INTEGRATION, SimTraffic, Wide Area Traffic Simulation (WATSim), VISSIM, and Parallel Microscopic Traffic Simulator (PARAMICS).

More information on traffic analysis tools can be found on the FHWA Office of Operations Traffic Analysis Tools web site, available at http://www.ops.fhwa.dot.gov/trafficanalysistools/index.htm (Accessed 9/16/05).

Work Zone Specific Analysis Tools

• QuickZone is a work zone delay estimation model developed by the Federal Highway Administration (FHWA) Research, Development, and Technology (RD&T) program. QuickZone was developed to help State and local transportation agencies better understand and consider the impacts of work zones as they plan, design, and implement their highway projects. QuickZone can help enable the consideration of the work zone impacts of alternate work zone design and mitigation strategies. QuickZone provides this capability to project planners and engineers, whereby they can obtain an estimate of delay, queuing, and user costs associated with alternate work zone design and mitigation strategies. The ability to estimate these work zone impacts at the early planning and design stages will facilitate better decision-making that will ultimately improve the operational performance of highways during construction and maintenance activities, and minimize the impacts on road users and businesses.
  
  QuickZone provides analysis options to estimate work zone delays and user costs for different demand patterns and for temporal (seasonal, weekly, daily) and spatial variations of work zone configurations. It can quantify corridor delay resulting from capacity decreases in work zones; identify the impact on delay of alternative construction phasing plans; and support tradeoff analyses between construction costs and delay costs. Work zone impacts and costs are estimated for an average day of work, which can then be amortized to get an estimate of average annual costs based on a user-specified life-cycle for the improvement. It can assess the impact of delay-mitigation strategies, such as alternate routing, signal re-timing, lane widening, and ramp metering. In addition to estimating work zone delays and user costs, QuickZone also provides a sketch-planning analysis of travel behavioral changes in response to work zones. QuickZone also supports the calculation of work-completion incentives.
  
  The software will therefore help highway agencies better phase and stage their construction and maintenance activities. For example, QuickZone enables road owners and contractors to compare the effects of doing highway work at night instead of during the day, or that of diverting traffic to one road versus another road at various stages of construction[2]. Information on QuickZone can be found at https://www.fhwa.dot.gov/research/topics/operations/travelanalysis/quickzone/ (Accessed 09/16/05).
• QUEWZ-98 is a microcomputer analysis tool for planning and scheduling freeway work zone lane closures. It analyzes traffic conditions on a freeway segment with and without a lane closure in place and provides estimates of the additional road user costs and of the queuing resulting from a work zone lane closure. The road user costs calculated include travel time, vehicle operating costs, and excess emissions. A user's manual for QUEWZ-98 is available. After describing the capabilities and input data requirements of QUEWZ-98, it provides instructions on using Q98MENU, a menu-driven user interface, to run QUEWZ-98. It also includes three examples to illustrate the various input and output options that are available. QUEWZ-98 can be obtained from McTrans at http://mctrans.ce.ufl.edu/ (Accessed 09/16/05).
• Construction Analysis for Pavement Rehabilitation Strategies (CA4PRS) is a computer model intended to estimate the maximum amount (distance) of highway that can be rehabilitated or reconstructed within various closure timeframes. This model integrates pavement, construction, and traffic related decision-making by balancing numerous constraints such as scheduling interfaces, pavement materials and design, contractor logistics and resources, and traffic operations. When combined with a traffic model, the CA4PRS software can help determine which pavement structures and rehabilitation strategies maximize on-schedule construction production without creating unacceptable traffic delays. More information on CA4PRS is available at http://www.dot.ca.gov/newtech/roadway/ca4prs/ca4prs.htm (Accessed 01/06/06), and http://www.ce.berkeley.edu/~eblee/CA4PRS.htm (Accessed 01/06/06).

Additional information on work zone analysis tools can be found at the Work Zone & Traffic Analysis/Management section of the FHWA work zone web site, available at http://ops.fhwa.dot.gov/wz/traffic_analysis.htm (Accessed 06/05/06).

Choice of Analysis Tools

There is no one analytical tool that can do everything or solve every problem. The method or tool selected for any analysis should be consistent with the analysis needs and fit within budget and resource requirements. Using too complex of a tool for the analysis needs, such as using a microsimulation tool for preliminary screening of scenarios, may result in a poor use of resources. At the same time, using too simplistic of a tool for the situation, for example using a travel demand model for detailed design of an operational strategy, may result in inaccurate or unreliable results.

Some tools, such as IDAS and DYNASMART-P, were not designed specifically for work zones but they can be used to analyze work zone situations. For example, IDAS may be used to analyze work zone situations in a planning context for a sketch-planning level analysis, while DYNASMART-P may be used to perform a more detailed operational analysis on a dynamic (time-varying) basis.

The FHWA Traffic Analysis Toolbox provides reference information on current tools and also presents a needs-based framework for selecting the appropriate tools. The Toolbox provides a spreadsheet-based tool selection framework that is based on user-specific analysis needs and criteria. The Toolbox is available at http://www.ops.fhwa.dot.gov/trafficanalysistools/toolbox.htm (accessed 06/05/06).

previous | next