Impacts of Millenial Student Loan Debt on Transportation Choices

The Federal Highway Administration’s Transportation Policy Unit has a series of reports on Transportation Futures. I was involved in one of them as an advisor to the consultant, though my name is not on the report, so I am not responsible. The report  is now online:

Figure 18. Transportation and Loan Payment as Percentage of Income
Figure 18. Transportation and Loan Payment as Percentage of Income


Impacts of Millenial Student Loan Debt on Transportation Choices

Now the largest generation in America, the Millennials are not driving at the same rates of their predecessor generations, the Baby Boomers and Generation X. There have been plenty of studies about the millennial generation’s lack of interest in driving. Many conclude that Millennials are fascinated by technology or urban culture.

According to AAA’s findings of the 2013 ‘Your Driving Costs’ study, annual automobile spending for an average sedan owner are $9,122 (Based on 15,000 miles annual usage). For someone newly out of college with student loan debt, automobile ownership may feel out of reach. Millennial student loan debt is a widely discussed topic. Approximately 40 million Americans hold student loan debt. Currently more than 70 percent of U.S. students who graduate with a bachelor’s degree leave with debt, averaging $28,400. According to the White House Council of Economic advisors, 61% of adult millennials attended college, compared to 46% of their Baby Boomer parents. In 2014, the total outstanding student loan debt in the US surpassed $1 trillion.

This paper attempts to investigate the impact of student loan debt along with other variables on the millennial transportation choices.


The data was tortured looking for a relationship. If there is one, it is weak. For instance see the finding buried on p. 34

“In general, cutting back on transportation expenses may not be a central priority for those with student loans, as their job earnings enable such individuals to handle rising transportation costs. Indeed, the data shows a positive relationship between income and student loan value (Figure 15).

Taking into account all student loan holders, the relationship between student loans and transportation expenses appears unclear. While some analyses suggest a slightly positive relationship (i.e., the uptick in transportation expenses for loan-holders), many of the other trends can be explained by Figure 15. Student loan holders in our data are generally well-off, which would contribute to higher transportation expenses.

Across the board, people spent less on transportation as a percentage of household expenditures post- 2008, but Millennials showed a particularly large difference between loan-holders (Figure 16, right) and those without loans (Figure 16, left). While we might consider this drop to be connected to student loan commitments, a number of analyses seem to refute this idea.”

Closing the Cahill Expressway at Circular Quay

Map of Cahill Expressway, Red line indicates section under discussion in this post.
Map of Cahill Expressway, Red line indicates section under discussion in this post.
The Cahill Expressway in Sydney, the city’s first expressway, opened in 1958, connecting the Eastern suburbs to the Harbour Bridge. After the Harbour Tunnel opened in 1992, traffic was halved, the section’s Eason or being eliminated. Looking at a map, you can see the Harbour Tunnel and Harbour Bridge approaches join north of the Harbour, and basically form an upside-down V-shape, with the Circular Quay section forming a cross, the segment turning the upside-down V into an A.

Traffic counts for the Cahill Expressway at Circular Quay are given for 2012 as about 20000 average annual daily traffic in each direction. While certainly non-trivial, this is also not a lot for two lanes in each direction, equivalent to a four-lane arterial. And when the system is working, all of this traffic has alternative routes, as the route is topologically similar to the classic Braess Paradox.

The Braess Paradox observes that under certain circumstances an additional link increases total travel time, and is dysfunctional, because of the difference between the costs that travellers pay and the costs they impose by congesting others. While it is hard to prove such cases in the real world, there is no reason for this link to exist in the post-Tunnel configuration except as a backup when the Harbour Tunnel is closed or constricted to divert traffic to the Harbour Bridge.

Circular Quay Railway Station, Cahill Expressway on the top deck.
Circular Quay Railway Station, Cahill Expressway on the top deck.
If this section of the Cahill were to be removed, many of its access and egress links could be removed as well, creating additional space and sunlight in the constricted central business district. Southbound traffic would decide north of Sydney whether to diverge for the East or West and then take the Bridge or Tunnel, with no recourse except for city streets. Northbound traffic from the East would take the tunnel to cross the Harbour or exit onto city streets. The operators of the tunnel should be pleased.


Suppose the Circular Quay section were closed. The expressway lies on the upper deck of a double-deck elevated structure, with an elevated railway (the under-rated John Bradfield‘s City Circle, completed in 1956)  immediately below. So the whole structure cannot easily come down. Instead the expressway deck can be repurposed, much like New York’s High Line and other infrastructure reuse projects, as a pedestrian overlook (there is already a sidewalk) on the north side, with the south side hosting restaurants and open-air cafes with a gorgeous view of the Harbour.* I am sure urban designers could come up with some lovely watercolour renderings.

Views like this from the Cahill Expressway at Circular Quay (photo from the train deck below)
While all of this undoubtedly requires study and many, many consultant contracts, it is really easy to test the actual traffic effects (and would make a nice Master’s Thesis project). Close the ramps for a few weeks “for repairs”. This must happen from time-to-time anyway.  Perhaps there is a ‘natural experiment’ coming up, or recently passed, when this happened. Monitor traffic elsewhere in the system. Evaluate the consequences.

The hypothesis is that traffic conditions are no worse overall (system travel time is unchanged or lower), though selected links may in fact be worse off while others are improved. Given the reduction in merges and diverges, I suspect more links are improved than worsened.

If this hypothesis is borne out, there is less total travel (fewer vehicle kilometres traveled) in the city, travel is faster, and most travellers are better off.

In recent decades there has been a trend for cities to close obsolete freeway sections. San Francisco famously took down the Embarcadero Freeway for instance, opening up the waterfront. Seoul removed the Cheongyecheon freeway and restored a river. There have been others. While removal of this section of the Cahill is not likely to have the same effects, as the elevated railway will remain, it still could be beneficial.  Proposals to demolish the entire Cahill, which bisects major parks the Botanical Gardens and the Domain have also been discussed, though burying them under air rights park seems a far simpler and less controversial proposal, and less like to strand the Harbour Tunnel.

Aerial Photo (via Apple Maps) of Cahill Expressway at Circular Quay, facing south. Red marks indicate extent of section.
Aerial Photo (via Apple Maps) of Cahill Expressway at Circular Quay, facing south. Red marks indicate extent of section.

* A single lane passage for emergency vehicle could be maintained if necessary.

Mo’ Rankings, Mo’ Bragging

I posted skeptically late last year On Academic Rankings. Some new rankings have come out, so it is time to brag or fret some more. The world renowned ARWU has come out with new rankings for Civil Engineering, and better still, for Transport.

I am pleased to report Sydney comes in 7th globally in Transport. None of this is my doing, I just got here, but nevertheless it is good to hear.

ARWU Transport Rankings

World Rank Institution* Country Total Score Score on
1 Delft University of Technology 274.9 100
2 Beijing Jiaotong University 267.5 79.9
3 University of California, Berkeley 265.5 86.3
4 University of Leeds 245.6 72.6
5 National University of Singapore 241.8 61.8
6 The Hong Kong University of Science and Technology 237.4 51.1
7 University of Sydney 236.7 78.7
8 The Hong Kong Polytechnic University 234.7 62.8
9 The University of Texas at Austin 230.9 73.8
10 Massachusetts Institute of Technology (MIT) 228.7 69.3
11 University of Maryland, College Park 228 74.9
12 Purdue University – West Lafayette 224.9 74.3
13 Georgia Institute of Technology 224.4 67.8
14 Tsinghua University 223.2 74

This is not how I would rank the universities, but feel free to look at the methodologies and construct your own.

The ARWU indicators and methodology are provided at:

Sydney comes in at 32 globally in Civil Engineering (a bigger arena than transport usually). Again I am not responsible, and this is not how I would rank them, and it sure is puzzling how this is how it came out, and sadly we are behind local rival UNSW, but that is being worked on …

ARWU Civil Engineering Rankings

World Rank Institution* Country Total Score Score on
1 Tongji University 313.1 100
2 Lehigh University 252.1 39.7
3 Swiss Federal Institute of Technology Zurich 250.9 63.9
4 The University of Texas at Austin 248.8 66.2
5 Polytechnic University of Madrid 226.9 59.4
6 Tsinghua University 226.1 85.8
7 National Technical University of Athens 217.2 54.7
8 University of California, Berkeley 213.7 72.6
8 University of Illinois at Urbana-Champaign 213.7 67.9
10 University of Canterbury 204.2 36.4
11 The University of New South Wales 202.4 59.2
12 Western University 201.9 42
13 University of California, San Diego 197.3 39.6
14 Nanyang Technological University 192.8 56.4
15 University of California, Davis 189.9 56.1
16 University at Buffalo, the State University of New York 185.3 40.3
17 The University of Tokyo 183.9 47.1
18 Texas A&M University 183.7 77.8
19 University of Toronto 181.7 50.9
20 Purdue University – West Lafayette 180.2 63.6
21 Dalian University of Technology 176.2 75.8
22 The Hong Kong Polytechnic University 174.4 76.6
23 Seoul National University 174.3 56
24 The University of Hong Kong 174.2 56.4
25 Swiss Federal Institute of Technology Lausanne 173.8 53.8
26 Delft University of Technology 173.3 75.5
26 University of Stuttgart 173.3 36
28 Virginia Polytechnic Institute and State University 172.8 59.2
29 McMaster University 172 36.4
30 Harbin Institute of Technology 171.7 69.4
31 Southeast University 170.6 73.8
32 University of Sydney 169.5 43.9
33 University of Michigan-Ann Arbor 168.3 48

An Introduction to the Network Weight Matrix

Recently published:

This study introduces the network weight matrix as a replacement for the spatial weight matrix to measure the spatial dependence between links of a network. This matrix stems from the concepts of betweenness centrality and vulnerability in network science. The elements of the matrix are a function not simply of proximity, but of network topology, network structure, and demand configuration. The network weight matrix has distinctive characteristics, which are capable of reflecting spatial dependence between traffic links: (1) elements are allowed to have negative and positive values capturing the competitive and complementary nature of links, (2) diagonal elements are not fixed to zero, which takes the self-dependence of a link upon itself into consideration, and (3) elements not only reflect the spatial dependence based on the network structure, but they acknowledge the demand configuration as well. We verify the network weight matrix by modeling traffic flows in a 3 × 3 grid test network with 9 nodes and 24 directed links connecting 72 origin-destination (OD) pairs. Models encompassing the network weight matrix outperform both models without spatial components and models with the spatial weight matrix. The network weight matrix represents a more accurate and defensible spatial dependency between traffic links, and offers the potential to augment traffic flow prediction.

Talk: Full Cost Analysis of Accessibility

The following research talk will be held on the University of Sydney campus on July 10. Let me know if you are interested in attending.

Comparing alternative paths
Comparing alternative paths

Title: Full Cost Analysis of Accessibility

Abstract: Accessibility measures the ease of reaching valuable destinations. For transport systems, accessibility combines travel costs and opportunities into a single metric, which represents both the transport network and land-use. Traditional accessibility metrics have been analyzed from the perspective of travel time – considering the time cost of travel. This fails to fully capture the full travel costs, especially the external costs of travel. In this presentation, a framework of extending accessibility analysis is proposed combining the significant cost components of travel, time, safety, emission and money, with accessibility analysis. By examining both private costs, which individual travelers consider when making travel decisions, and external costs, which society should consider when making investment decision, this approach better aligns accessibility with the goals of evaluation for transportation planning. A proof-of-concept analysis based on a toy network was conducted to prove the practicability of the framework. The current studies focus on the implementation of the framework on Minneapolis-St.Paul metropolitan region.

Bio: Mengying Cui is a Ph.D. Candidate in the Department of Civil, Environmental and Geo-Engineering at the University of Minnesota, and working in the Accessibility Observatory of the Center for Transportation Studies at the university. Mengying earned her bachelor of engineering degree (2011) in logistics engineering from Tongji University and a master of engineering degree (2014) in transportation planning and management from Dalian University of Technology. Her research interests in accessibility evaluations, transport economics, network reliability and GIS in transportation. She has been granted Matthew J. Huber Award for Excellence in Transportation Research and Education (2017).

When: Monday July 10, 2017, 14:00 – 15:00 pm AEST

Where: Room 438 | School of Civil Engineering Building J05  | The University of Sydney | NSW | 2006

Elon Musk’s Chicago Tunnel makes a dumb idea even dumber | Wired

I was interviewed by Aarian Marshall of Wired for Elon Musk’s Chicago Tunnel makes a dumb idea even dumber. My quote:

Be skeptical, too, of Chicago’s promises that any contractor—Boring Company included—will pay for this tunnel’s construction and maintenance all on its lonesome. Public transportation construction and operations are rarely profitable, says David Levinson, a transportation engineer at the University of Sydney. “There’s no way fares will cover the capital costs of a tunnel,” he says. “If you made everyone take this train, maybe.”

The Surprisingly Not Terrible Urban Interface of McDonald’s in Alexandria, NSW

Recently I berated a hotel in Shanghai for not welcoming pedestrians from a corner. I have since come across a McDonald’s, shown in the images, which makes an effort to welcome pedestrians from the adjacent intersection, with an opening at the corner, and a clearly delineated and non-circuitous pedestrian path across the driveway to the otherwise typical and un-urban store configuration.

I don’t know the history, I imagine  there was once a typical corner hotel/pub that for whatever reason (abandonment, fire, changing market) became a McDonald’s site. The planners insisted on maintaining the semblance of urbanity at the corner, and this was the compromise. One day there will be a real building again. Until that day, I have seen far worse.



On the Differences between Autonomous, Automated, Self-Driving, and Driverless Cars

Today we have cars. In 30 years we will have cars. But in the meantime, some cars will will driven by humans and others not, and there will be terms to distinguish them.

Today, most people use the terms Autonomous, Automated, Self-Driving, and Driverless as interchangeable. Even wikipedia does not differentiate. Yet some people in the field make a point of the differences (e.g. Alain Kornhauser). If I understand these differences correctly, a self-driving car is not as advanced as driverless, in that driverless doesn’t have the back-up of a person taking control, and self-driving might. Driverless taxis are not merely self-driving, they pick up passengers and may be personless. In SAE terms, driverless is Level 5, while self-driving is Level 4 or below.

Generally, the difference between automatic (or automated) and autonomous is the degree of human intervention. An automated car does not have the level of intelligence or independence that an autonomous car has. So driverless and autonomous are nearer to synonyms, as are self-driving and automated. A truly autonomous car would decide on destination and route as well as control within the lanes. An automated car would follow orders about destination and route, and may only adopt some lane-keeping or car-following guidance.

Google/Waymo car, soon to be retired
Google/Waymo car, soon to be retired

Nevertheless, I do not believe these differences can be preserved linguistically, even within the profession, the broad misuse and confusion will drown small differences of meaning.

Etymology online gives the following:

autonomous (adj.) Look up autonomous at Dictionary.com1800, “pertaining to autonomy;” 1804, “subject to its own laws,” from Greek autonomos “having one’s own laws,” of animals, “feeding or ranging at will,” from autos “self” (see auto-) + nomos “law” (from PIE root *nem- “assign, allot; take”). Compare privilege. Used mostly in metaphysics and politics; see autonomic. Related: Autonomously.

automated (adj.) Look up automated at Dictionary.com1952, American English, adjective based on automation.

The Transportist: June 2017

Welcome to the June 2017 issue of The Transportist. As always you can follow along at the blog or on Twitter.

Transport Posts

[posts as in jobs or positions]

Transportist Posts

[posts as in blog posts]





Media Appearances

Transport News


  • The New Season of Utopia [Dreamland] starts Wednesday July 19 on . The best show about urban planning in Australia.







(The worst month for Uber)





Land Use

Infrastructure Week






By Us

By Others

Call for Papers