Browsing by Author "Merlin, Louis A."

Now showing 1 - 4 of 4
  • Thumbnail Image
    Item
    Longitudinal analysis of adolescent girls' activity patterns in San Diego and Minneapolis: Understanding the influence of the transition to licensure
    (Journal of Transport and Land Use, 2016) McDonald, Noreen C.; Merlin, Louis A.; Hu, Haoting; Shih, Joshu; Cohen, Deborah A.; Evenson, Kelly R.; McKenzie, Thomas L.; Rodriguez, Daniel A.
    The proportion of teens and young adults with driver's licenses has declined sharply in many industrialized countries including the United States. Explanations for this decline have ranged from the introduction of graduated driver licensing programs to the increase in online social interaction. We used a longitudinal cohort study of teenage girls in San Diego and Minneapolis to evaluate factors associated with licensure and whether teens’ travel patterns become more independent as they age. We found that licensure depended not only on age but also on race and ethnicity as well as on variables that correlate with household income. Results also showed evidence that teen travel became more independent as teens aged, and that acquiring a license is an important part of this increased independence. However, we found limited evidence that teens' travel-activity patterns changed as a result of acquiring a driver’s license. Rather, teen independence resulted in less parental chauffeuring but little shift in travel patterns. For the larger debate on declining millennial mobility, our results suggest the need for more nuanced attention to variation across demographic groups and consideration of the equity implications if declines in travel and licensure are concentrated in low-income and minority populations.
  • Thumbnail Image
    Item
    A new method using medians to calibrate single-parameter spatial interaction models
    (Journal of Transport and Land Use, 2020) Merlin, Louis A.
    I present a method for calibrating the impedance parameter of a gravity spatial interaction model using only the median travel time as a measure of observed traveler behavior. Complete information about the spatial structure of origins, destinations, and travel times between origins and destinations is also required. Using Monte Carlo simulation techniques on stylized cities, I attempt to recover true (a priori known) impedance values with this method for a range of impedance values for both negative exponential and power impedance functions. The results are compared with estimates obtained by other fast methods. The proposed method proves to provide a fairly accurate estimate of the impedance parameter, with a mean percent error typically below 20% and often below 10% for common impedance values. The proposed method is an improvement over existing calibration methods in several respects. First, it allows for the estimation of the impedance parameter directly without lengthy iterative calculations. Second, because it only requires median travel times, it can be calibrated with smaller samples (n~200), allowing the construction of gravity models for specific modes and/or travel purposes. And third, the method does not require expensive travel demand software and so can be implemented more widely in practice.
  • Thumbnail Image
    Item
    A portrait of accessibility change for four US metropolitan areas
    (Journal of Transport and Land Use, 2017) Merlin, Louis A.
    Accessibility is a key objective of regional planning, one requiring the coordination of transportation and land use. Several metropolitan planning organizations in the United States and Europe have started to incorporate accessibility metrics into their evaluation of future regional scenarios. This paper describes changes in accessibility to employment by auto and transit for four contrasting metropolitan areas between 2000 and 2010. The effect of changing residential locations, changing employment locations, and changing travel speeds on accessibility change is decomposed and analyzed. Residential locations are generally shifting toward low-accessibility locations, degrading regional accessibility. Shifting employment locations have differential effects across metros, improving the accessibility of central locations in some metros while improving the accessibility of peripheral locations in others. Travel speeds also show strongly contrasting patterns across metros, with speed-related accessibility benefits concentrated in high-density locations for some metros (Chicago), while low-density locations are the primary beneficiary in other metros (Charlotte and St. Louis).
  • Thumbnail Image
    Item
    Residential accessibility's relationships with crash rates per capita
    (Journal of Transport and Land Use, 2020) Merlin, Louis A.; Cherry, Chris R.; Mohamadi-Hezaveh, Amin; Dumbaugh, Eric
    This paper examines the relationship between residential accessibility, i.e., accessibility from a person's home address, and their likelihood of being in a crash over a three-year period. We explore two potential relationships with accessibility. The first is that persons who live in areas with high destination accessibility may drive less and therefore are less likely to be in vehicular crashes. The second is that persons who live in high vehicle miles traveled (VMT) accessibility areas may be exposed to higher levels of traffic in their regular activity space and therefore may be more likely to be in crashes of all modal types. Examining traffic analysis zones in Knoxville, Tennessee, this research finds some evidence for each of these hypothesized effects. These oppositely directed effects have dominant influence within different travel-time thresholds. The first relationship between destination accessibility and fewer crashes is found to be strongest for 10-minute auto accessibility, whereas the second relationship between VMT accessibility and more crashes is found to occur at 10-minute, 20-minute, and 30-minute thresholds.