Recent papers of Nexus Group

Our research group has released a slew of working papers this week: Working Papers – Nexus: Researching Networks, Economics & Urban Systems
These are listed below





  • Liao, Chen-Fu, Henry Liu, and David Levinson (2008) Engaging Undergraduate Students in Transportation Studies through Simulating
    Transportation for Realistic Engineering Education and Training (STREET)

    The practice of transportation engineering and planning has evolved substantially over the past several decades. A new paradigm for transportation engineering education is required to better engage students and deliver knowledge. Simulation tools have been used by transportation professionals to evaluate and analyze the potential impact of design or control strategy changes. Conveying complex transportation concepts can be effectively achieved by exploring them through simulation. Simulation is particularly valuable in transportation education because most transportation policies and strategies in the real world take years to implement with a prohibitively high cost. Transportation simulation allows learners to apply different control strategies in a risk-free environment and to expose themselves to transportation engineering methodologies that are currently in practice. Despite the advantages, simulation, however, has not been widely adopted in the education of transportation engineering. Using simulation in undergraduate transportation courses is sporadic and reported efforts have been focused on the upper-level technical elective courses. A suite of web-based simulation modules was developed and incorporated in the undergraduate transportation courses at University of Minnesota. The STREET (Simulating Transportation for Realistic Engineering Education and Training) research project was recently awarded by NSF (National Science Foundation) to develop web-based simulation modules to improve instruction in transportation engineering courses and evaluate their effectiveness. Our ultimate goal is to become the epicenter for developing simulation-based teaching materials, an active textbook, which offers an interactive learning environment to undergraduate students. With the hand-on nature of simulation, we hope to improve student understanding of critical concepts in transportation engineering and student motivation toward transportation engineering, and improve student retention in the field. We also would like to disseminate the results and teaching materials to other colleges to integrate the simulation modules in their curricula.

    Keywords: Transportation Education and Training, Transportation Simulation, Roadway Geometry Design
    (working paper).




  • Tilahun, Nebiyou and David Levinson (2008) Home Relocation and the Journey to Work
    Relocation decisions are complex. Each household has a bundle of attributes that make a location attractive to it, including the ability to access different activity locations easily, neighborhood quality, house amenities etc. Relocating households have an opportunity to ?nd housing closer to their work. Using data collected in the Twin Cities area, we investigate how distance to home and travel time to home change among individuals who have changed their residence since they started their current job. Comparing the home-to-work distance after the move to the previous-home-to-work distance, we ?nd that the average home to work distance is reduced as a result of the move. We also ?nd that the reduction depend on the previous home to work distance as well as the previous homes’ proximity to downtown Minneapolis. The ?ndings show that households that are either very close to their work, or very close to downtown, or both did not signi?cantly increase or decrease their commute after relocation. This suggests that access to work as well as access to the opportunities that proximity to downtown offers (to jobs, urban spaces, etc.) are important in the decision making process.

    Keywords: Commuting, Location, Journey-to-Work, Tenure
    (working paper).




  • Iacono, Michael and David Levinson (2008) Predicting Land Use Change: How Much Does Transportation Matter?
    In this paper, we propose to measure the extent of the influence of transportation systems on land use change. Using a set of high-resolution land use data for the Twin Cities metropolitan region, we estimate logistic regression models of land use change covering a 10-year period from 1990 to 2000. The models account for existing land use types, neighboring land uses, and transportation network variables that measure the physical proximity of highway networks, as well as the level of accessibility associated with a speci?c location. The models are estimated with and without the transportation variables and compared to assess the extent of their influence. We ?nd (perhaps not surprisingly) that transportation-related variables exert some influence on changes to land use patterns, though not as much as variables representing existing and neighboring land uses.

    Keywords: Land use, Twin Cities (Minnesota), Mathematical models, urban growth
    (working paper).




  • Iacono, Michael and David Levinson (2008) Review of Methods for Estimating the Economic Impact of Transportation Improvements
    Transportation analysts and the public decision-makers they support are confronted with a broad range of analytical tools for estimating the economic impacts of improvements to transportation networks. Many of the available models operate at different scales and have distinctly different structures, making them more or less appropriate for analyzing the impacts of different types of projects. Here, we review several of the economic methods and models that have been developed for analyzing the impact of transportation improvements, giving special attention to types of projects that add highway capacity in urban areas. We review project-based methods, including bene?t-cost analysis and several analytical software tools developed by the Federal Highway Administration (FHWA) for economic analysis of transportation investment.
    We then move on to aggregate and disaggregate-level econometric methods, including regional economic models, hedonic price functions, production functions and cliometric analyses. We also devote some attention to the role of induced demand in economic evaluation, since it is often one of the most uncertain and confounding factors faced by those charged with conducting economic evaluation of transportation projects.

    Keywords: Economic Impact, Benefit-Cost Analysis, Literature Review
    (working paper).




  • Zhu, Shanjiang and David Levinson (2008) A Review of Research on Planned and Unplanned Disruptions to Transportation Networks
    Travel decisions may be very stable in an environment with which they are familiar. Ma jor network disruptions such as the I-35W bridge collapse disrupt habitual behavior. Such “natural” experiments provide unique opportunities for behavioral studies, but the time window for such studies is limited. A well-developed methodology is crucial for both data collection and analysis, and thus the soundness of behavioral models , especially in such a limited time window. Therefore, this paper reviews both theoretical and empirical studies on traffic and behavioral impacts of network disruptions. Findings from this paper offer prospective ideas about capturing the impacts of network disruption.

    Keywords: Network disruption; Travel survey; Travel behavior
    (working paper).




  • Parthasarathi, Pavithra and David Levinson (2008) Post-Construction Evaluation of Traf?c Forecast Accuracy
    This research evaluates the accuracy of demand forecasts using a sample of recently-completed projects in Minnesota and identi?es the factors influencing the inaccuracy in forecasts. The forecast traf?c data for this study is drawn from Environmental Impact Statements (EIS), Transportation Analysis Reports (TAR) and other forecast reports produced by the Minnesota Department of Transportation (Mn/DOT) with a horizon forecast year of 2010 or earlier. The actual traf?c data
    is compiled from the database of traf?c counts maintained by the Of?ce of Traf?c Forecasting and Analysis section at Mn/DOT. Based on recent research on forecast accuracy, the (in)accuracy of traf?c forecasts is estimated as a ratio of the forecast traf?c to the actual traf?c. The estimation of forecast (in)accuracy also involves a comparison of the socioeconomic and demographic assumptions, the assumed networks to the actual in-place networks and other travel behavior assumptions that went into generating the
    traf?c forecasts against actual conditions. The analysis indicates a general trend of underestimation in roadway traf?c forecasts with factors such as highway type, functional classi?cation, direction playing an influencing role. Roadways with higher volumes and higher functional classi?cations such as freeways are subject to underestimation compared to lower volume roadways/functional classi?cations. The comparison
    of demographic forecasts shows a trend of overestimation while the comparison of travel behavior characteristics indicates a lack of incorporation of fundamental shifts and societal changes.

    Keywords: Traffic Forecast, Travel Demand Model, Transportation Planning
    (working paper).




  • Huang, Arthur and David Levinson (2008) The Effects of Daylight Saving Time on Vehicle Crashes in Minnesota
    Daylight saving time (DST), implemented as an energy saving policy, impacts many other aspects of life; one is road safety. Based on ten-year vehicle crash data in Minnesota, this paper evaluates long- and short-term effects of DST on daily vehicle crashes, as well as daily fatal crashes. Our statistical models not only include weather conditions and days of week as independent variables, but also consider traf?c volume count on road. Our ?ndings show that DST, in the long run, is associated with fewer daily crashes than standard time (ST). Yet, DST is found to be associated with higher odds of having more fatal crashes than ST. In addition, our data rejects the hypothesis that the ?rst Sunday or Monday of time change in spring is associated with more fatigue-related crashes than Sundays before time change; nor do we ?nd that the ?rst Sunday or Monday of time change in fall is associated with more alcohol-related crashes than Sundays before time change. Of all weather conditions, snow is found to have the most signi?cant effect on vehicle crashes; however, its impact on fatal crashes is nevertheless not statistically different from clear weather. Furthermore, Friday is associated with the most daily crashes, whereas Sunday and Saturday are associated with higher odds of more fatal crashes than weekdays.

    Keywords: daylight saving time, vehicle crashes, fatal crashes, traf?c volume
    (working paper).




  • Huang, Arthur and David Levinson (2008) An Agent-based Retail Location Model on a Supply Chain Network
    Clusters of business locations, which considerably impact daily activities, have been prominent phenomena. Yet the question of how and why ?rms cluster in certain areas has not been suf?ciently studied. This paper investigates the emergence of clusters of business locations on a supply chain network comprised of suppliers, retailers, and, consumers. Krugman (1996) argued that urban concentration involved a tension between the “centripetal? and the “centrifugal? forces. Based on that notion, this research proposes an agent-based model of retailers’ location choice in a market of homogeneous products. In this game, retailers endeavor to maximize their pro?ts by changing locations. Retailers’ distribution patterns are measured by entropy and cluster density. Simulation results reveal that as more retailers engage in the game, clusters autonomously emerge and the entropy of clusters increases. Once retailers exceed a certain number, average density of clusters begins to decline; all discrete clusters gradually merge to a large cluster, spreading out uniformly. This research thus ?nds that the centripetal
    force attracts retailers to supplier locations; with even more retailers entering the market, the centrifugal force disperses them. The sensitivity results on model parameters and consumers’ demand elasticity are also discussed.

    Keywords: clustering, supply chain network, location choice, distribution pattern
    (working paper).




  • Geroliminis, Nikolas and David Levinson (2008) Cordon Pricing Consistent with the Physics of Overcrowding
    This paper describes the modeling of recurring congestion in a network. It is shown that the standard economic models of marginal cost cannot describe precisely traffic congestion in networks during time-dependent conditions. Following a macroscopic traffic approach, we describe the equilibrium solution for a congested network in the no-toll case. A dynamic model of cordon-based congestion pricing (such as for the morning commute) for networks is developed consistent with the physics of traffic. The paper combines Vickrey’s theory with a macroscopic traffic model, which is readily observable with existing monitoring technologies. The paper also examines some policy implications of the cordon-based pricing to treat equity and reliability issues, i.e. in what mobility level a city should choose to operate. An application of the model in a downtown area shows that these schemes can improve mobility and relieve congestion in cities.

    Keywords: congestion pricing, traffic models, macroscopic fundamental diagram
    (working paper).




  • Wu, Xinkai, David Levinson, and Henry Liu (2008) Perception of Waiting Time at Signalized Intersections
    Perceived waiting time at signalized intersections differs from the real value, and varies with signal design. The onerousness of delay depends on the conditions under which it is experienced. Using weighted travel time time may contribute to optimal signal control if its use can improve upon assuming that all time is weighted equally by users. This research explores the perception of waiting time at signalized intersections based on the results of an online survey, which directly collected the perceived waiting time and the user ratings of the signal designs of each intersection on an arterial including 3 intersections. Statistically analyzing the survey data suggests the perception of waiting time is a function of the real time; and a quadratic model better can describes relationship. The survey also indicates that there exists a tradeoff between the total waiting time and the individual waiting time of each intersection. It turns out that drivers prefer to split the total waiting time at different intersections at the price of a longer total wait if the difference of the total waiting time of two signal designs is within 30 seconds. The survey data shows that the perceived waiting time, instead of the real waiting time, better explains how users will rate the individual signal designs for both intersections and arterials including multiple intersections.

    Keywords: delay, perceived time, traffic signals
    (working paper).




  • Zhu, Shanjiang, David Levinson, Henry Liu, and Kathleen Harder (2008) The Traffic and Behavioral Effects of the I-35W Mississippi River Bridge collapse
    The collapse, on August 1, 2007, of the I-35W bridge over the Mississippi River in Minneapolis, abruptly interrupted the usual route of about 140,000 daily vehicle trips and substantially disturbed the flow pattern on the network. It took several weeks for the network to re-equilibrate, during which period, travelers continued to learn and adjust their travel decisions. A good understanding of this process is crucial for traffic management and designing mitigation schemes. A survey collected behavioral responses to the bridge collapse. Traffic data were also collected to understand the traffic conditions experienced by road users. Data from both resources are analyzed and compared. Findings of behavioral effects of capacity changes could have signi?cant implications for travel demand modeling, especially of day-to-day travel demand.

    Keywords: I-35W bridge collapse, travel behavior, travel survey
    (working paper).




  • Xie, Feng and David Levinson (2008) How Streetcars Shaped Suburbanization: A Granger-Casality Analysis of Land Use and Transit in The Twin Cities
    This paper presents a causality analysis of the coupled development of population and streetcars in the Twin Cities metropolitan area. Historic residence and network
    data were assembled for 1900-1930, and linear cross-sectional time-series models were estimated at both a tract and block level using this data. It is found that, in contrast with transportation systems that were expanded in response to increased demand, the rapid expansion of the streetcar system during the electric era has been driven by other forces and to a large extent led land development in the Twin Cities. The main forces that have driven this process include technological superiority, monopoly, close connections with real estate business, and people’s reliance on the streetcar for mobility. Proximity to the streetcar is found to be a crucial factor that determines the distribution and development of residences: it is observed that residential density declines with the distance from streetcar lines, and signi?cantly drops beyond a walkable distance; it is also observed that gaining a closer access to streetcar lines within 800 meters (about a half mile) predicts the increase in residential density to a signi?cant extent.

    Keywords: streetcars, light rail transit, land use and transportation, development, Twin Cities (Minnesota), network growth
    (working paper).




  • Xie, Feng and David Levinson (2008) Evaluating the Effects of I-35W Bridge Collapse on Road-Users in the Twin Cities Metropolitan Region
    This study evaluates the effects of I-35W bridge collapse on road-users in the Twin- Cities metropolitan area. We adopted the Twin-Cities (Metropolitan Minneapolis
    and St. Paul) Seven-County travel demand model developed in previous research, recalibrated it against July 2007 loop detector traffic data, and used this model to carry out an evaluation of economic loss incurred by increased travel delay in alternative scenarios before and after the bridge collapse. We concluded that the failure of the I-35W bridge resulted in an economic loss of $71,000 to $220,000 a day, depending on how flexible road-users in the system can adjust their trip destinations in response to the bridge closing. We also estimated that the ma jor traffic restoration projects Mn/DOT has implemented in quick response to the bridge collapse can save road-users $9,500 to $17,500 a day. This translates into a bene?t-cost ratio of 2.0-9.0, suggesting these pro jects are highly bene?ciary in an economic sense. In this analysis, the use of a simpli?ed, scaled-down travel demand model enabled us to carry out the analysis quickly and accurately, showing its contributions in transportation planning under situations such as emergency relief and comprehensive design.

    Keywords: I-35W Bridge Collapse, Twin Cities (Minnesota), economic evaluation
    (working paper).




  • Patterson, Tyler and David Levinson (2008) Lexus Lanes or Corolla Lanes? Spatial Use and Equity Patterns on the I-394 MnPASS Lanes
    A 2004-2006 longitudinal panel survey of I-394 residents found support levels at over 60 percent for the congestion priced High Occupancy Toll (HOT) lane, known to the Twin Cities as MnPASS. This number varies only slightly when sorted by income levels, gender, and education levels, suggesting that the arrangement is perceived as equitable.
    However, people with higher incomes use the system more often and thereby capitalize on the direct benefit more often, a finding consistent with other studies. Previous research has not revealed whether higher incomes actually cause people to use the MnPASS option more often or whether HOT lanes have simply been built along high income corridors, such as I-394. This paper aims to separate the effects of income and location on use to provide a more robust understanding of equity concerns. Using data provided by the Minnesota Department of Transportation, Heteroskedasticity-Consistent
    Method 3 (HC3) regressions, this paper suggests that location and income both explain
    HOT lane use.

    Keywords: Congestion Pricing, HOT Lanes, High Occupancy Toll lanes, Value Pricing, Equity, Twin Cities (Minnesota), economic evaluation
    (working paper).