the traveler costs of unplanned transport network disruptions: an activity-based approach erik...
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The traveler costs of unplanned transport network disruptions:
An activity-based approach
Erik Jenelius Royal Institute of Technology, SwedenLars-Göran Mattsson Royal Institute of Technology, Sweden
David Levinson University of Minnesota
Background
• How to value increases in travel time due to unplanned transport network disruptions (floods, snowfall, severe car crashes etc.)?
• In cost-benefit analysis
• For bonus provision for restoration work
• State of practice: Standard value of time
• Related but different: Value of reliability/variability
travel timeaverage travel time
variability
extreme events
Aim
• Build theoretical foundation for the traveller delay costs of unplanned transport network disruptions
• Capture the following aspects:• Large delays – marginal values may be misleading• Long disruptions – more than one trip may be affected• Unexpected events, imperfect information – less ability to
adjust travel and daily schedule optimally• Flexibility – smaller intrusion of delay• Time of day – less room for schedule adjustments later
Framework
• Trips are made between two activities, e.g., home and work
• Costs arise as we rather spend time at home or at work than in car
• Schedule preferences expressed as utility maximization
• We consider three activities (”morning”, ”work”, ”evening”), two trips (”morning commute”, ”evening commute”)
• Calibration against empirical results from Tseng & Verhoef (2008)
Variables
• Marginal activity and travel utilities: u1(t), u2(t – ξts2), u3(t), ν
• Marginal utility of activity 2 (work) may depend on arrival time:Parameter ξ controls schedule flexibility: ξ = 0 clock-time only ξ = 1 duration only
• Travel times T1, T2 (assumed exogenous here, departure time dependent in paper)
• Departure times td1, td2, arrival times ts2 = td1 + T1, ts3 = td2 + T2
The model
• Daily utility U determined by departure times
Travel costs
• To avoid new notation, assume utility is money metric. Marginal WTP functions for activity/travel transitions:
• Assume optimally timed trips normally
• FOC and marginal VOT can be found
• Travel cost
Delay costs
• Journey delays T1, T2
• Delay costs
• Depend on:• journey delays (magnitude and distribution)• schedule adjustments (information)• work schedule flexibility
Adjustments
• Evidence from I-35W bridge collapse
• We consider:
1. no adjustment
2. no + optimal
3. over-adjustment
4. over + optimal
5. optimal adjustment
Calibration
• Calibrated against time-varying WTP for home/work from Tseng & Verhoef (2008) and some findings from Hess et al. (2007)
• Parameterized logistic functions for marginal WTP functions1(t), 2(t – ts2), 3(t): min, max, steepness, location
Numerical results
• Delay on both morning and evening trip (baseline tr. time 240 min)
• Fixed (left) vs. flexible (right) work hours
Numerical results
• Delay on morning trip only or evening trip only
• Fixed (left) vs. flexible (right) work hours
Some conclusions
• Delay costs increase rapidly with length of delay
• Better adjustments (information) can reduce costs significantly
• Flexible work hours great if journey delay occurs early
• Previous model-based valuations of disruption impacts (I-35W bridge collapse etc.) have probably underestimated delay costs
• We here only considered work trips and individuals’ own stated costs
Thank you!