Volvo Center

A Review of Green Logistics Schemes Used in Cities Around the World

Geroliminis, Nikolaos
Daganzo, Carlos F.
2005

Freight carriers strive to provide higher levels of transportation service with lower costs. However, the economic and environmental viability of cities are negatively affected by the present organization of urban goods distribution. Can these two competitive goals be harmonised to create efficient and environmentally friendly urban logistics systems? This paper presents several examples of “green logistics” schemes tried in a number of forward-looking cities around the world. The review highlights the basic qualitative ideas of these schemes and the results of field tests. Most of the...

On the Stability of Freeway Traffic

Daganzo, Carlos F.
2010

Traffic flow theory is used to analyze the spatio-temporal distribution of flow and density on closed loop homogeneous freeways with many ramps, which produce inflows and allow outflows. It is shown that if the on-ramp demand is space-independent then this distribution tends toward uniformity in space if the freeway is either: (i) uncongested; or (ii) congested with queues on its on-ramps and enough inflow to cause the average freeway density to increase with time. In all other cases, including any recovery phase of a rush hour where the freeway's average density declines, the distribution...

Allocating city space to multiple transportation modes: A new modeling approach consistent with the physics of transport

Gonzales, Eric J.
Geroliminis, Nikolas
Cassidy, Michael J.
Daganzo, Carlos F.
2008

A macroscopic modeling approach is proposed for allocating a city’s road space among competing transport modes. In this approach, a city or neighborhood street network is viewed as a reservoir with aggregated traffic. Taking the number of vehicles (accumulation) in a reservoir as input, we show how one can reliably predict system performance in terms of person and vehicle hours spent in the system and person and vehicle kilometers traveled. The approach is used here to unveil two important results: first, that restricting access to a city’s congested areas can improve mobility for all...

An analytical approximation for the macropscopic fundamental diagram of urban traffic

Daganzo, Carlos F
Geroliminis, Nikolas
2008

This paper shows that a macroscopic fundamental diagram (MFD) relating flow and average density must exist on any street with blocks of diverse widths and lengths, but no turns, even if all or some of the intersections are controlled by arbitrarily timed traffic signals. The timing patterns are assumed to be fixed in time. Exact expressions in terms of a shortest path recipe are given, both, for the street’s capacity and its MFD. Approximate formulas that require little data are also given.Conditions under which the results can be approximately extended to networks encompassing large city...

On the perceptibility of safety systems

Grembek, Offer
Daganzo, Carlos F.
2010

The perceptibility of a safety system is defined as the extent to which the system can be perceived by the senses or the mind. The objective here is to study which safety systems are more easily perceived by the user and to identify design attributes that affect this level of perception. A web-based, pairwise comparison survey was conducted to evaluate the perceptibility of fifteen safety systems ranging from traffic safety systems to consumer safety. The analytic hierarchy process was applied to estimate the perceptibility levels and rank the safety systems. The results show that...

Urban Densities and Transit: A Multi-dimensional Perspective

Cervero, Robert
Guerra, Erick
2011

This paper investigates the relationship between transit and urban densities in the United States. An analysis of light rail systems finds that a residential density of about 30 people per gross acre near stations is needed to in order to make them among the top 25 percent of rail transit investments in terms of cost effectiveness; for heavy rail systems, the density is 45 people per gross acre. Increasing density around stations would greatly increase ridership, particularly when jobs are located within one-quarter mile of the stations and housing is located within one-half mile....

Deploying Underutilized Bus Lanes at Key Nodes in a Road Network

Guler, Ilgin
Cassidy, Michael
2010

The authors of this working paper explain that the operation of buses in mixed traffic flow can be impeded by congestion, leading to unreliable and slow service. Similarly, buses that stop frequently for passengers interfere with the flow of general traffic. Dedicated lanes provide a means for buses to bypass car queues, but in cases where bus flow is low, converting a general purpose lane to a bus-only lane will delay car traffic. The authors describe innovative schemes for deploying bus lanes to serve low bus demand intermittently. Strategies to deploy underutilized bus lanes will be...

Direct Ridership Model of Bus Rapid Transit in Los Angeles County

Cervero, Robert
Murakami, Jin
Miller, Mark A.
2009

A Direct Ridership Model (DRM) for predicting Bus Rapid Transit (BRT) patronage in Southern California is estimated. Attributes of bus stops and their surroundings constitute the data observations of the DRM, enabling a fairly fine-resolution of analysis to be carried out on factors that influence ridership. The best-fitting DRM revealed that service frequency strongly influences BRT patronage in Los Angeles County. High intermodal connectivity, with both feeder bus routes and rail-transit services, also significantly induces BRT travel. Population densities also contribute to BRT...

Clockwise Hysteresis Loops in the MacroscopicFundamental Diagram

Gayah, Vikash V.
Daganzo, Carlos F.
2010

A recent study reported that the Macroscopic Fundamental Diagram of a medium size city exhibited a clockwise hysteresis loop on a day in which a major disturbance caused many drivers to switch to unfamiliar routes. This paper shows that clockwise loops are to be expected when there are disturbances, especially if the disturbances cause a significant fraction of the drivers to not change routes adaptively. It is shown that when drivers are not adaptive networks are inherently more unstable as they recover from congestion than as they are loaded. In other words, during recovery congestion...

Existence of urban-scale macroscopic fundamental diagrams: Some experimental findings

Geroliminis, Nikolas
Daganzo, Carlos F.
2007

A field experiment in Yokohama (Japan) reveals that a macroscopic fundamental diagram (MFD) linking space-mean flow, density and speed exists on a large urban area. The experiment used a combination of fixed detectors and floating vehicle probes as sensors. It was observed that when the somewhat chaotic scatter-plots of speed vs. density from individual fixed detectors were aggregated the scatter nearly disappeared and points grouped neatly along a smoothly declining curve. This evidence suggests, but does not prove, that an MFD exists for the complete network because the fixed detectors...