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1. Introduction: Work Order Objectives

The Federal Highway Administration (FHWA) supports operational improvements to reduce delay and congestion throughout the country. In many cases it has been determined that relatively minor reductions in peak traffic can result in major reductions in delay for all travelers. The FHWA wanted to test this premise for the Washington, DC region, and engaged SAIC (supported by the Louis Berger Group) to carry out the research study. The study approach is designed to answer specific research questions, as summarized in the Tables below.

The first objective of this research is to produce empirical evidence of the changes in rush hour traffic demand (volumes) and delays for weekdays in early August, relative to other months of the year, in the Washington, DC metropolitan area. The three broad questions to be answered for this objective and the approaches to answering the questions are:

Research Question Approach
What is the amount and percentage of reductions in weekday peak period traffic on freeways in (early) August in the Washington, DC area, when traffic congestion is reduced significantly relative to other (non-summer) months? (Section 2) Evaluate traffic count and speed data at selected locations at different times and dates, ideally where (and when) GPS probe data are available to demonstrate free flow and congested conditions.
What is the relationship between peak period and peak-hour traffic reduction and delay reduction on freeways, i.e., how much delay might be reduced by various levels of reductions in traffic? (Section 2) Graph and analyze speed – volume relationships to determine “tip points” for congestion and delay versus free flow conditions
Given the above relationships, how much traffic needs to be taken off freeways operating at various levels of congestion in the metropolitan area, to restore free flow during rush hours? (Section 2) Calculate values and percentages for selected locations from analysis, above, extrapolate to larger regional relationship

The second objective is to identify the approximate numbers and proportions of persons traveling on the congested freeways who may be able to shift their time of travel to off peak periods, or shift their mode of travel to high-occupancy vehicles. The three questions to be answered and the approaches are:

Research Question Approach
What is the share of travel that is made for various purposes other than commuting on congested freeways during peak periods in the Washington, DC area? (Section 3) Perform in-depth analysis on Metropolitan Washington Council of Governments (MWCOG) 1994 Household Travel Survey[3] – identify trip chains by time of day, by trip purpose, and travel time. MWCOG conducted a detailed household travel survey in 2007 but the data will not be available until mid-2009, and thus was not available for this study
What share of these travelers may have some flexibility to shift their time of travel to off-peak periods? (Section 3) Identify subsets of survey with greater likelihood to be able to shift travel times, review literature for appropriate definitions of “discretionary trips”
What is the potential for other modes (e.g., transit, vanpools, carpools, etc.) to attract additional mode share, if free-flow service on all freeways were guaranteed to these modes through aggressive and active traffic management strategies such as congestion pricing? (Section 4) Conduct literature review on travel demand management and mode shifts in analogous situations, summarize results

[3] MWCOG conducted a detailed household travel survey in 2007 but the data will not be available until mid-2009, and thus was not available for this study

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