Rick Donnelly

Urban Freight Models

The chapter discusses specific challenges and applications for modelling urban distribution. In fact, the analyses of urban freight transport traditionally focus only on restocking flows and usually neglect shopping flows. But the end-consumer choices in relation to type of purchasing undoubtedly impact on freight distribution flows and the end-consumer shopping choices depend on the commercial supply with respect to residence and on end-consumer behaviour, which in turn depends on some characteristics such as age, income, family dimension and lifestyle. Starting from literature, the paper reviews models for the urban freight movements, mapping the behaviour of the retailers and some aspects of the end consumers that generate freight movements in an urban context. Two macro-segments in the last miles of the freight supply chain are identified, with the retail outlet as final decoupling point: the segment upstream, between firms (push movements), and the segment downstream, between consumer and retailer (pull movements).

Advanced Practices in Travel Forecasting

This study explores the use of travel modeling and forecasting tools that represent significant advances over the current state of practice. The study includes five types of models: activity-based demand, dynamic network, land use, freight, and statewide. Information was gathered through literature review; detailed interviews among federal, state, and metropolitan agencies, and consulting firms; and case studies.

Gradual rasterization: redefining spatial resolution in transport modelling

It is a challenge to find the appropriate level of spatial resolution in transport modelling. While the zone system has substantial influence on model results, the resolution and design of zones is rarely analyzed systematically, and even less commonly adjusted to a specific modelling need. In this paper we present a new methodology to automatically create a new zone system based on the quadtree algorithm specific to transport modelling. Gradual raster cells are generated, where smaller raster cells tend to be used in urban areas and larger raster cells dominate in low-density, rural areas. As changing the zonal resolution affects the number of intrazonal and interzonal trips, an algorithm has been developed that adjusts intrazonal trips in line with the network resolution. Trip tables of a travel demand model for the state of Georgia, USA were disaggregated using this new zone system of gradual raster cells. The traffic assignment results validate significantly better than when using the original zone system.

A model for national freight flows, distribution centers, empty trucks and urban truck movements

ABSTRACT Trucks travel both short distances for local deliveries and long distances for transporting goods across the country. Often their travel behavior is tour-based, they run under tight schedules and under curfew on selected roads. Despite these differences from personal travel, in practice truck models largely follow person travel methods. To overcome this shortcoming, a two-layer truck model is developed for the Chicago Metropolitan Area. Long-distance trucks are driven by commodity flows, with distribution centers, rail yards, marine ports and airports being represented explicitly. Empty trucks are accounted for as well. For the short-distance truck model, a novel parameter estimation method makes use of limited data to derive region-specific parameters. The model is fully operational and validates reasonably well against traffic counts.

From Macro to Microscopic Trip Generation: Representing Heterogeneous Travel Behavior

Received: September 19, 2016 Revised: December 18, 2016 Accepted: January 06, 2017 Abstract: Background: In four-step travel demand models, average trip generation rates are traditionally applied to static household type definitions. In reality, however, trip generation is more heterogeneous with some households making no trips and other households making more than a dozen trips, even if they are of the same household type.