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Browsing by Author "Wu, Yao"

Now showing 1 - 2 of 2
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    Improving the Estimation of Travel Demand for Traffic Simulation: Part II
    (2004-12) Wu, Yao; Davis, Gary; Levinson, David
    This report examined several methods for estimating Origin- Destination (OD) matrices for freeways using loop detector data. Least squares based methods were compared in terms of both off- line and on- line estimation. Simulated data and observed data were used for evaluating the static and recursive estimators. For off- line estimation, four fully constrained least squares methods were compared. The results showed that the variations of a constrained least squares approach produced more efficient estimates. For on- line estimation, two recursive least squares algorithms were examined. The first method extends Kalman Filtering to satisfy the natural constraints of the OD split parameters. The second was developed from sequential quadratic programming. These algorithms showed different capabilities to capture an abrupt change in the split parameters. Practical recommendations of the choice of different algorithms are given.
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    The Rational Locator Re-examined
    (Springer, 2005) Levinson, David M; Wu, Yao
    The Rational Locator Hypothesis posits that individuals can, if they choose, maintain approximately steady journey-to-work travel times by adjusting their home and workplace. This hypothesis was coupled with the observation of long-term stability in drive alone journey-to-work times in metropolitan Washington (those times were unchanged from 1957 through 1968 to 1988). Despite the increase of average commuting distance and congestion, trip duration remained constant or even declined when controlling for travel purpose and travel mode because of shifting a share of traffic from slow urban routes to faster suburban routes. This observation has significance, as it is important to know for travel demand analysis if there is an underlying budget, or even a regularity, as this helps us determine whether our forecasts are reasonable. To retest the underlying rationale for the hypothesis: that travel times are stable, both intra-metropolitan and inter-metropolitan comparisons of travel times are made. The intra-metropolitan analysis compared Washington DC data from 1968, 1988, and 1994, and Twin Cities data from 1990 and 2000. The results depend upon geography. For the larger Washington DC region, keeping the same geography shows little change in commute times, but using the larger 1994 area suggests an increase in commute times.However, the Twin Cities, starting from a much shorter commute time, shows a marked increase over the decade, using either the smaller or the larger geography. To explain the differences between the two areas, an inter-metropolitan analysis conducts a series of regressions on mean metropolitan travel time for the 65 largest metropolitan areas in theUnited States. The average commute time varies (positively) in these cities as a function of congestion and population density-both significant at the 99 percent confidence interval.Geographical area, population, and income were also significant at the 90 percent confidence interval. Despite the continuing observation of stability in drive alone commuting times in metropolitan Washington, we reject the theory of personal commuting budgets, as we find that not only are commuting times not generally stable over time at the intra-metropolitan area, but that commuting time clearly depends on metropolitan spatial structure.