Recently in Reliability Category

I get interviewed about the reliability measures of the new Urban Mobility Report by Ariel Hart of the Atlanta Journal-Constitution: Atlanta traffic bad but predictable :

"‘People care about this,’ said David Levinson, a professor of civil engineering at the University of Minnesota who researches traffic psychology surrounding reliability. People will even accept more congestion to get more reliability, he said, and he has a mathematical formula to calculate how much.

‘It’s the surprises, the inconsistency of the delay that makes it difficult,’ costing people social capital with colleagues, clients and friends when they are unexpectedly late, he said."

The reliability ratio, the ratio of the value of reliability to the value of time us about 1, depending on how it is measured. See

• Carrion, Carlos and David Levinson (2012) Value of Travel Time Reliability: A review of current evidence. Transportation Research part A 46(4) 720--741.

Recently published

Carrion, Carlos and David Levinson (in press) Valuation of travel time reliability from a GPS-based experimental design Transportation Research part C [doi]:

"In the Minneapolis–St. Paul region (Twin Cities), the Minnesota Department of Transportation (MnDOT) converted the Interstate 394 High Occupancy Vehicle (HOV) lanes to High Occupancy Toll (HOT) lanes (or MnPASS Express Lanes). These lanes allow single occupancy vehicles (SOVs) to access the HOV lanes by paying a fee. This fee is adjusted according to a dynamic pricing system that varies with the current demand. This paper estimates the value placed by the travelers on the HOT lanes because of improvements in travel time reliability. This value depends on how the travelers regard a route with predictable travel times (or small travel time variability) in comparison to another with unpredictable travel times (or high travel time variability). For this purpose, commuters are recruited and equipped with Global Positioning System (GPS) devices and instructed to commute for two weeks on each of three plausible alternatives between their home in the western suburbs of Minneapolis eastbound to work in downtown or the University of Minnesota: I-394 HOT lanes, I-394 General Purpose lanes (untolled), and signalized arterials close to the I-394 corridor. They are then given the opportunity to travel on their preferred route after experiencing each alternative. This revealed preference data is then analyzed using discrete choice models of route. Three measures of reliability are explored and incorporated in the estimation of the models: standard deviation (a classical measure in the research literature); shortened right range (typically found in departure time choice models); and interquartile range (75th–25th percentile). Each of these measures represents distinct ways about how travelers deal with different sections of reliability. In all the models, it was found that reliability was valued highly (and statistically significantly), but differently according to how it was defined. The estimated value of reliability in each of the models indicates that commuters are willing to pay a fee for a reliable route depending on how they value their reliability savings."

Recently Published: Carrion, Carlos and David Levinson (2012) Value of travel time reliability: A review of current evidence. Transportation Research Part A: Policy and Practice 46(4) 720--741.[doi]

Travel time reliability is a fundamental factor in travel behavior. It represents the temporal uncertainty experienced by travelers in their movement between any two nodes in a network. The importance of the time reliability depends on the penalties incurred by the travelers. In road networks, travelers consider the existence of a trip travel time uncertainty in different choice situations (departure time, route, mode, and others). In this paper, a systematic review of the current state of research in travel time reliability, and more explicitly in the value of travel time reliability is presented. Moreover, a meta-analysis is performed in order to determine the reasons behind the discrepancy among the reliability estimates.

Keywords: Variability; Reliability; Travel time; Scheduling; Meta-analysis

Recently published: Carrion-Madera, Carlos, David Levinson, and Kathleen Harder (2011) Value of Travel-Time Reliability: Commuters' Route-Choice Behavior in the Twin Cities (OTREC-RR-11-21):

"Travel-time variability is a noteworthy factor in network performance. It measures the temporal uncertainty experienced by users in their movement between any two nodes in a network. The importance of the time variance depends on the penalties incurred by the users. In road networks, travelers consider the existence of this journey uncertainty in their selection of routes. This choice process takes into account travel-time variability and other characteristics of the travelers and the road network. In this complex behavioral response, a feasible decision is spawned based on not only the amalgamation of attributes, but also on the experience travelers incurred from previous situations. Over the past several years, the analysis of these behavioral responses (travelers’ route choices) to fluctuations in travel-time variability has become a central topic in transportation research. These have generally been based on theoretical approaches built upon Wardropian equilibrium, or empirical formulations using Random Utility Theory. This report focuses on the travel behavior of commuters using Interstate 394 (I-394) and the swapping (bridge) choice behavior of commuters crossing the Mississippi River in Minneapolis. The inferences of this report are based on collected Global Positioning System (GPS) tracking data and accompanying surveys. Furthermore, it also employs two distinct approaches (estimation of Value of Reliability [VOR] and econometric modeling with travelers’ intrapersonal data) in order to analyze the behavioral responses of two distinct sets of subjects in the Minneapolis-Saint Paul (Twin Cities) area."

Network Reliability on the Electric Grid (from Miller-McCune Debunking Theories of a Terrorist Power Grab

Hines and Blumsack's study ... shows that the most vulnerable points are the ones that have the most energy flowing through them -- like huge power stations or highly connected transformers.

Article Do topological models provide good information about electricity
infrastructure vulnerability?

I think there is something to learn about generalizing network reliability and vulnerability across fields (electricity, transportation, etc.). Network structure, and the underlying technology, matter.

At the 28th International
System Safety Conference 2010 30 Aug-03 Sep 2010 in Minneapolis, I will give a keynote on Aug 31 (at 8 am) on the Rise and Fall of the I-35W Mississippi River Bridge. It looks like an interesting conference. I am sure there is a lot to be learned at the intersection of system safety and network reliability.

• Carrion-Madera, Carlos and David Levinson (2010) Value of Travel Time Reliability: A review of current evidence

Travel time reliability is a fundamental factor in travel behavior. It represents the temporal uncertainty experienced by users in their movement between any two nodes in a network. The importance of the time reliability depends on the penalties incurred by the users. In road networks, travelers consider the existence of a trip travel time uncertainty in different choice situations (departure time, route, mode, and others). In this paper, a systematic review of the current state of research in travel time reliability, and more explicitly in the value of travel time reliability is presented. Moreover, a meta-analysis is performed in order to determine the reasons behind the discrepancy among the reliability estimates.

The International Symposium on Transportation Network Reliability is now on a semi-quinquennial cycle: the next (5th) will be in December 2012 in Hong Kong. This will be followed by the 6th meeting in Summer of 2015 in Japan. INSTR is thus the first conference series (to our knowledge) to meet on a cycle of four meetings per decade.

As host of the 4th INSTR, I want to extend my thanks to the following for making it work smoothly:

(1) The Center for Transportation Studies for donating the time and effort of Stephanie Malinoff through the long preparation period and Stephanie and Liz Erickson on the conference days. Also to Arlene Mathison for coordinating the website.

(2) College of Continuing Education for coordinating the logistics, in particular Catherine Flannery, Kristi Fischer, Nicole Freese, Tonya Walsh, and Sara Van Essendelft

(3) Brian Kary of MnDOT for giving the opening plenary talk

(4) Taylor and Francis for sponsorship

(5) Bill Hyman for helping distribute the announcement and encouraging attendance among those in the SHRP program

(6) Peer reviewers for taking the time to review the papers

(7) My colleague Henry Liu for co-hosting and helping with organization, and with ground transportation, with his student Sean He and post-doc Xiaolei Guo

(8) Restaurant facilities (Tea House and Campus Club) and the caterers for handling everything smoothly, as well as the Hotels (Days and Ramada), as well as the facilities at Coffman.

(9) Authors and participants for attending.

I hope to see everyone in Hong Kong.

The Fourth triennial INternational Symposium on Transportation network Reliability (INSTR) starts tomorrow morning at the University of Minnesota campus in Minneapolis. We have a pre-conference dinner tonight at Tea House. The symposium program is available at the website. We look forward to seeing everyone.

Recent working paper:

• Carlos, Carrion-Madera, and Levinson, David, (2010), Value of Reliability: High Occupancy Toll Lanes, General Purpose Lanes, and Arterials, No 000073, Working Papers, University of Minnesota: Nexus Research Group.

In the Minneapolis-St. Paul region (Twin Cities), the Minnesota Department of Transportation (MnDOT) converted the Interstate 394 High Occupancy Vehicle (HOV) lanes to High Occupancy Toll (HOT) lanes (or MnPASS Express Lanes). These lanes allow single occupancy vehicles (SOV) to access the HOV lanes by paying a fee. This fee is adjusted according to a dynamic pricing system that varies with the current demand. This paper estimates the value placed by the travelers on the HOT lanes because of improvements in travel time reliability. This value depends on how the travelers regard a route with predictable travel times (or small travel time variability) in comparison to another with unpredictable travel times (or high travel time variability). For this purpose, commuters are recruited and equipped with Global Positioning System (GPS) devices and instructed to commute for two weeks on each of three plausible alternatives between their home in the western suburbs of Minneapolis eastbound to work in downtown or the University of Minnesota: I-394 HOT lanes, I-394 General Purpose lanes (untolled), and signalized arterials close to the I-394 corridor. They are then given the opportunity to travel on their preferred route after experiencing each alternative. This revealed preference data is then analyzed using mixed logit route choice models. Three measures of reliability are explored and incorporated in the estimation of the models: standard deviation (a classical measure in the research literature); shortened right range (typically found in departure time choice models); and interquartile range (75th - 25th percentile). Each of these measures represents distinct ways about how travelers deal with different sections of reliability. In all the models, it was found that reliability was valued highly (and statistically significantly), but differently according to how it was defined. The estimated value of reliability in each of the models indicates that commuters are willing to pay a fee for a reliable route depending on how they value their reliability savings.

The 4th International Symposium on Transportation Network Reliability draft agenda is now available for download. The conference will be held July 22-23, 2010, University of Minnesota. We look forward to seeing you here.

Recently published:

Zhang, Lei, and David M. Levinson (2008) Investing for Reliability and Security in Transportation Networks. Transportation Research Record: Journal of the Transportation Research Board #2041 pp.1-10 [doi]

Alternative transportation investment policies can lead to very different network forms in the future. The desirability of a transportation network should be assessed not only by its economic efficiency but also reliability, because the cost of incidental capacity loss in a road network can be massive. This research concerns how investment rules shape the hierarchical structure of roads, and affects network fragility with regard to natural disasters, congestion, and accidents and vulnerability to targeted attacks. A microscopic network growth model predicts the equilibrium road networks under two alternative policy scenarios: investment based on benefit cost analysis or bottleneck removal. A set of Monte-Carlo simulation runs, in which a certain percentage of links are removed according to the type of network degradation analyzed, are carried out to evaluate the equilibrium road networks. It is found that hierarchy exists in road networks for reasons such as economic efficiency, but an overly hierarchical structure has serious reliability problems. Throughout the equilibrating or evolution process, the studied grid network under benefit cost analysis has better efficiency performance, as well as error and attack tolerance. The policy implication from these findings is that benefit-cost analysis should be preferred to myopic bottleneck-removal type of investment rules, no matter how the planning horizon is specified.

Keywords: Transportation network dynamics, road growth model, reliability, vulnerability, fragility, road investment and financing policy