Number of items: **3**.

## F

Flyvbjerg, Bent,

Skamris Holm, Mette K. and

Buhl, Soren L.
(2003)

*How common and how large are cost overruns in transport infrastructure projects?*
Transport Reviews, 23 (1).
pp. 71-88.
Link to full text available through this repository.

- Abstract
Despite the hundreds of billions of dollars being spent on infrastructure development — from roads, rail and airports to energy extraction and power networks to the Internet — surprisingly little reliable knowledge exists about the performance of these investments in terms of actual costs, benefits and risks. This paper presents results from the first statistically significant study of cost performance in transport infrastructure projects. The sample used is the largest of its kind, covering 258 projects in 20 nations worth approximately US$90 billion (constant 1995 prices). The paper shows with overwhelming statistical significance that in terms of costs transport infrastructure projects do not perform as promised. The conclusion is tested for different project types, different geographical regions and different historical periods. Substantial cost escalation is the rule rather than the exception. For rail, average cost escalation is 45% (SD=38), for fixed links (tunnels and bridges) it is 34% (62) and for roads 20% (30). Cost escalation appears a global phenomenon, existing across 20 nations on five continents. Cost estimates have not improved and cost escalation not decreased over the past 70 years. Cost estimates used in decision-making for transport infrastructure development are highly, systematically and significantly misleading. Large cost escalations combined with large standard deviations translate into large financial risks. However, such risks are typically ignored or underplayed in decision-making, to the detriment of social and economic welfare.

- Item type
- Article
- Subject(s)
- UNSPECIFIED
- Uncontrolled keywords
- Transport; infrastructure projects; cost overruns
- Centre
- BT Centre for Major Programme Management

## L

López, Eduardo,

Carmi, Shai,

Havlin, Shlomo,

Buldyrev, Sergey and

Stanley, Eugene
(2006)

*Anomalous electrical and frictionless flow conductance in complex networks.*
Physica D: Nonlinear Phenomena, 224 (1-2).
pp. 69-76.
Link to full text available through this repository.

- Abstract
We study transport properties such as electrical and frictionless flow conductance on scale-free and Erdős–Rényi networks. We consider the conductance G between two arbitrarily chosen nodes where each link has the same unit resistance. Our theoretical analysis for scale-free networks predicts a broad range of values of G, with a power-law tail distribution , where gG=2λ−1, where λ is the decay exponent for the scale-free network degree distribution. We confirm our predictions by simulations of scale-free networks solving the Kirchhoff equations for the conductance between a pair of nodes. The power-law tail in leads to large values of G, thereby significantly improving the transport in scale-free networks, compared to Erdős–Rényi networks where the tail of the conductivity distribution decays exponentially. Based on a simple physical ‘transport backbone’ picture we suggest that the conductances of scale-free and Erdős–Rényi networks can be approximated by ckAkB/(kA+kB) for any pair of nodes A and B with degrees kA and kB. Thus, a single quantity c, which depends on the average degree of the network, characterizes transport on both scale-free and Erdős–Rényi networks. We determine that c tends to 1 for increasing , and it is larger for scale-free networks. We compare the electrical results with a model for frictionless transport, where conductance is defined as the number of link-independent paths between A and B, and find that a similar picture holds. The effects of distance on the value of conductance are considered for both models, and some differences emerge. Finally, we use a recent data set for the AS (autonomous system) level of the Internet and confirm that our results are valid in this real-world example.

- Item type
- Article
- Subject(s)
- UNSPECIFIED
- Uncontrolled keywords
- Complex networks; Transport; Diffusion; Conductance; Scaling
- Centre
- CABDyN Complexity Centre

## S

Sreenivasan, Sameet,

Cohen, Reuven,

López, Eduardo,

Toroczkai, Zoltán and

Stanley, Eugene
(2007)

*Structural Bottlenecks for Communication in Networks.*
Physical Review E (Statistical, Nonlinear, and Soft Matter Physics), 75 (3).
036105.
Link to full text available through this repository.

- Abstract
We consider the effect of network topology on the optimality of packet routing which is quantified by γc, the rate of packet insertion beyond which congestion and queue growth occurs. We show that for any network, there exists an absolute upper bound, expressed in terms of vertex separators, for the scaling of γc with network size N, irrespective of the static routing protocol used. We then derive an estimate to this upper bound for scale-free networks and introduce a static routing protocol, the “hub avoidance protocol,” which, for large packet insertion rates, is superior to the shortest path routing protocol.

- Item type
- Article
- Subject(s)
- UNSPECIFIED
- Uncontrolled keywords
- Transport; Routing; Network congestion
- Centre
- CABDyN Complexity Centre

This list was generated on **Tue Mar 20 03:19:30 2018 WET**.