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    <copyright>Copyright © 2026. National Academy of Sciences. All rights reserved.</copyright>
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    <managingEditor>tris-trb@nas.edu (Bill McLeod)</managingEditor>
    <webMaster>tris-trb@nas.edu (Bill McLeod)</webMaster>
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      <title>Transport Research International Documentation (TRID)</title>
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    <item>
      <title>Exploring paradigm shift impacts in urban mobility: Autonomous Vehicles and Smart Cities</title>
      <link>https://trid.trb.org/View/1568879</link>
      <description><![CDATA[Urban mobility is a dynamic system that has had a (slow) natural evolution. Scientists and engineers are currently developing new mobility technologies. A progressive paradigm shift will change everything from the fuel type to the way of driving vehicles. Vehicles will progressively become autonomous and will communicate and cooperate with each other. In the long run, profound changes are expected in mobility as a service. Furthermore, urban areas will have a higher level of development, and cities will likely turn into Smart Cities in which the vehicles will interact with the urban infrastructure. The main objective of this paper is to explore the macroscopic effects of mobility interaction in a radial-circular urban road system for current and future cities (Smart Cities). In the literature, there is documentation of the direct effects of autonomous vehicles, but some indirect effects will cause undesirable impacts such as an increase in demand and more congestion, which change the demand behavior and the urban structure. Finally, this paper exhibits the results of direct and indirect effects calculated through analytical tools (Continuous Approximation Method). In fact, the authors' research shows that if demand increases by about 50%, the current scenario could have the same total cost as the future scenario with autonomous vehicles. Moreover, if the city radius increases by about 33% and the subjective value of time decreases about 20%, the benefits of the autonomous cars will be compensated. Therefore, the paper proves that autonomous vehicles could encourage the urban sprawl in the long run. Finally, Administrations should define transport strategies and policies to control these externalities, because autonomous driving could deteriorate mobility even worse than it is now.]]></description>
      <pubDate>Mon, 03 Dec 2018 12:05:42 GMT</pubDate>
      <guid>https://trid.trb.org/View/1568879</guid>
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      <title>Continuous approximation for demand balancing in solving large-scale one-commodity pickup and delivery problems</title>
      <link>https://trid.trb.org/View/1502631</link>
      <description><![CDATA[The one-commodity pickup and delivery problem (1-PDP) has a wide range of applications in the real world, e.g., for repositioning bikes in large cities to guarantee the sustainable operations of bike-sharing systems. It remains a challenge, however, to solve the problem for large-scale instances. This paper proposes a hybrid modeling framework for 1-PDP, where a continuum approximation (CA) approach is used to model internal pickup and delivery routing within each of multiple subregions, while matching of net surplus or deficit of the commodity out of these subregions is addressed in a discrete model with a reduced problem size. The interdependent local routing and system-level matching decisions are made simultaneously, and a Lagrangian relaxation based algorithm is developed to solve the hybrid model. A series of numerical experiments are conducted to show that the hybrid model is able to produce a good solution for large-scale instances in a short computation time.]]></description>
      <pubDate>Fri, 16 Mar 2018 09:52:01 GMT</pubDate>
      <guid>https://trid.trb.org/View/1502631</guid>
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      <title>Advancements in continuous approximation models for logistics and transportation systems: 1996–2016</title>
      <link>https://trid.trb.org/View/1493561</link>
      <description><![CDATA[Continuous approximation (CA) is an efficient and parsimonious technique for modeling complex logistics problems. In this paper, the authors review recent studies that develop CA models for transportation, distribution and logistics problems with the aim of synthesizing recent advancements and identifying current research gaps. This survey focuses on important principles and key results from CA models. In particular, the authors consider how these studies fill the gaps identified by the most recent literature reviews in this field. The authors observe that CA models are used in a wider range of applications, especially in the areas of facility location and integrated supply chain management. Most studies use CA as an alternative and a complement to discrete solution approaches; however, CA can also be used in combination with discrete approaches. The authors conclude with promising areas of future work.]]></description>
      <pubDate>Mon, 22 Jan 2018 10:48:16 GMT</pubDate>
      <guid>https://trid.trb.org/View/1493561</guid>
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    <item>
      <title>Continuous Approximation for Skip-Stop Operation in Rail Transit</title>
      <link>https://trid.trb.org/View/1259075</link>
      <description><![CDATA[Operating speed of a transit corridor is a key characteristic and has many consequences on its performance. It is generally accepted that an increased operating speed for a given fleet leads to reduced operating costs (per kilometer), travel and waiting times (three changes that can be computed precisely), an improved comfort and level of service, which can attract new passengers who are diverted from automobile (items harder to estimate precisely). That is why several operation schemes which aim to increase the operating speed are studied in the literature, such as deadheading, express services, stop skipping, etc.  A novel category of solutions to this problem for one-way single-track rail transit is to perform accelerated transit operations with fixed stopping schedules. The concept is quite simple: as the time required for stopping at each station is an important part of travel time, reducing it would be a great achievement. Particular operations that take advantage of this idea already exist. This paper focuses on one of them: the skip-stop operation for rail transit lines using a single one-way track. It consists in defining three types of stations: AB stations where all the trains stop, and A and B stations where only half of the trains stop (stations type A and B are allocated interchangeably). This mode of operation is already described in the literature [1–3] and has been successfully implemented in the Metro system of Santiago, Chile.  This work tackles the problem with a continuous approximation approach. The problem is described with a set of geographically dependent continuous parameters like the density of stations for a given line. Cost functions are built for a traditional (all-stop) operation and for skip-stop operation as described above. A simple example is presented to support this discussion. Finally, a discussion about the type of scenarios in which skip-stop operations are more beneficial is presented.]]></description>
      <pubDate>Tue, 03 Sep 2013 12:26:15 GMT</pubDate>
      <guid>https://trid.trb.org/View/1259075</guid>
    </item>
    <item>
      <title>A continuous approximation approach for assessment routing in disaster relief</title>
      <link>https://trid.trb.org/View/1248322</link>
      <description><![CDATA[In this paper, the authors focus on the assessment routing problem which routes teams to different communities to assess damage and relief needs following a disaster. To address time-sensitivity, the routing problem is modeled with the objective of minimizing the sum of arrival times to beneficiaries. The authors propose a continuous approximation approach which uses aggregated instance data to develop routing policies and cost approximations. Numerical tests are performed that demonstrate the effectiveness of the cost approximations at predicting the true implementation costs of the policies and compare the policies against more complex solution approaches. The continuous approximation approach yields solutions which can be easily implemented; further, this approach reduces the need for detailed data and the computational requirements to solve the problem.]]></description>
      <pubDate>Thu, 09 May 2013 09:07:12 GMT</pubDate>
      <guid>https://trid.trb.org/View/1248322</guid>
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    <item>
      <title>Further Investigation on Urban Cooperative Delivery Strategies at the Firm Level</title>
      <link>https://trid.trb.org/View/1234714</link>
      <description><![CDATA[A data set obtained from Treasure Valley, Idaho, which contains firm level information as well as detailed pickup/delivery tour information such the business type of every stop on the tour, enable this project to extend previous work to incorporate the critical supply chain and logistics decisions at the firm level. The Idaho data together with the night-time delivery survey data to be collected from a major grocery store chain in the Chicago region will be used to fine tune the ongoing work on urban consolidation/cooperative delivery project, in which a logistics cost model has been developed based on the Continuous Approximation (CA) method.]]></description>
      <pubDate>Thu, 03 Jan 2013 15:18:09 GMT</pubDate>
      <guid>https://trid.trb.org/View/1234714</guid>
    </item>
    <item>
      <title>Modeling the Airline Hub Location and Optimal Market Problems with Continuous Approximation Techniques</title>
      <link>https://trid.trb.org/View/1130886</link>
      <description><![CDATA[This paper presents continuous approximation techniques for the airline hub location and optimal market problems and demonstrates the usefulness of continuous approximation modeling in airline operations and network design through numerical studies. Specifically, this study proposes continuous approximation models for airline operations in restricted and unrestricted one-hub systems. The continuous approximation models presented in this paper will facilitate strategic planning of many-to-many airline distribution systems. Results from the continuous model can provide guidelines for constructing solutions for the discrete models. Using the proposed models, the effects of changing demand over years on the optimal hub location are evaluated. The 5% indifference area of the optimal hub location is also analyzed in order to investigate the sensitivity of the studied logistic problem to the hub location. The impact of a competitive airline network structure with regard to the hub location is also studied. This study addresses a gap in the airline operations literature on modeling the optimal market for an airline in a competitive structure with multi-airlines and already located hubs.]]></description>
      <pubDate>Tue, 26 Jun 2012 09:19:31 GMT</pubDate>
      <guid>https://trid.trb.org/View/1130886</guid>
    </item>
    <item>
      <title>Time slot management in attended home delivery</title>
      <link>https://trid.trb.org/View/1115862</link>
      <description><![CDATA[Narrow delivery time slots are offered by many e-tailers providing home delivery, especially e-grocers, in order to ensure satisfactory customer service. A complex planning problem results when the choice of delivery time slots has to balance marketing and operational considerations. The problem of selecting the set of time slots to offer in each of the zip codes in a service region is studied in this paper. Not only does the selection need to facilitate cost-effective delivery routes, but also needs to ensure an acceptable level of service to the customer. A fully automated approach is presented that is capable of producing high-quality delivery time slot offerings in a short amount of time. The value of this approach and the impact of the environment on the underlying trade-offs are revealed in computational experiments.]]></description>
      <pubDate>Wed, 14 Sep 2011 11:13:16 GMT</pubDate>
      <guid>https://trid.trb.org/View/1115862</guid>
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    <item>
      <title>A Continuum Approximation Approach to Reliable Facility Location Design under Correlated Probabilistic Disruptions</title>
      <link>https://trid.trb.org/View/915572</link>
      <description><![CDATA[This paper studies the reliable uncapacitated fixed charge location problem (RUFL) where facilities are subject to spatially correlated disruptions that occur with location-dependent probabilities (due to reasons such as natural or man-made disasters). If a facility fails, its customers are diverted to other facilities and incur excessive transportation cost. The authors develop a continuum approximation (CA) model to minimize the sum of initial facility construction costs and expected customer transportation costs under normal and failure scenarios. The paper presents ways to formulate the correlation among adjacent facility disruptions, and incorporates such correlations into the CA model. Numerical experiments are conducted to illustrate how the proposed model can be used to optimize facility location design, and how the correlations influence the total system cost.]]></description>
      <pubDate>Sun, 30 May 2010 07:44:14 GMT</pubDate>
      <guid>https://trid.trb.org/View/915572</guid>
    </item>
    <item>
      <title>Performance and Design of Mobility Allowance Shuttle Transit Services: Bounds on the Maximum Longitudinal Velocity</title>
      <link>https://trid.trb.org/View/793392</link>
      <description><![CDATA[There is a need for a transit system that provides flexible service at a cost-efficient price.  This article describe the mobility allowance shuttle transit (MAST) system, a concept the merges the flexibility of demand responsive transit (DRT) with the low-cost operability of fixed-route bus systems.  The authors develop bounds on the maximum longitudinal velocity to evaluate the performance and help the design of MAST services.  A MAST system allows buses to deviate from the fixed path so that customers within the service area may be picked up or dropped off at their desired locations.  However, the main purpose of these services is still to transport customers along a primary direction. The velocity along this direction should remain above a minimum threshold value to maintain the service attractive to customers.  The authors use continuous approximations to compute lower and upper bounds for realistic operating conditions.  Their analysis shows that a two-vehicle system, with selected widths of the service area of 0.5 miles and 1 mile, is able to serve, respectively, a demand of at least 10 and 7 customers per longitudinal mile of the service area while maintaining a reasonable forward progression velocity of about 10 miles/hour.  The relationships obtained by these calculations can be helpful in the design of MAST systems to set the main parameters of the service, such as slack time and headway.]]></description>
      <pubDate>Tue, 28 Nov 2006 11:31:18 GMT</pubDate>
      <guid>https://trid.trb.org/View/793392</guid>
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