Airport Capacity, Airport Delay, and Airline Service Supply: The Case of DFW Faculty and Staff: D. Gillen, M. Hansen, A. Kanafani, J. Tsao Visiting Scholar: G. Nero and Students: S. A. Huang and W. Wei Institute of Transportation Studies University of California at Berkeley 1 Presentation Outline Background Study/Motivation Delay Changes Airline Adaptations to New Capacity Conclusions & Future Work 2 1
Background 1/96 Changes at DFW New runway (October 1) Airspace redesign (October 1) Expected Capacity Impacts VFR: from 12 to 146 operations/hr IFR: from 66 to 18 operations/hr Expected Benefit 75% increase in regional capacity; 15-25% nationwide Research Questions How did delay change? How did airlines adapt? 3 Airport Average Arrival Delay (against schedule, per flight) 25 Average Flight Delay ATL DFW 2 ORD Average Delay per Flight 15 1 5 Jan-96-5 Feb-96 Mar-96 Apr-96 May-96 Jun-96 Jul-96 Aug-96 Sep-96 Oct-96 Nov-96 Dec-96 Jan-97 Feb-97 Month Mar-97 Apr-97 May-97 Jun-97 Jul-97 Aug-97 Sep-97 Oct-97 Nov-97 Dec-97 Jan-98 Feb-98 4 2
Airline System Arrival Delay 18 16 14 (against schedule, per flight) AA AS DL UA WN 12 Minutes 1 8 6 4 2 95-1Q 95-2Q 95-3Q 95-4Q 96-1Q 96-2Q 96-3Q 96-4Q 97-1Q 97-2Q 97-3Q 97-4Q 98-1Q Time 5 Schedule Padding Compare AA scheduled flight (gate to gate) time between DFW and 2 largest airports in January 96 and January 98 Find AA scheduled flight times increased by 4 minutes On - time performance initiative Accounts for DFW and AA delay changes 6 3
Effective Flight Time Effective Flight Time (EFT) is the time between scheduled departure and actual arrival of a flight. EFT is unaffected by changes in scheduled flight time. EFT can be decomposed into departure delay, taxi time, and airborne time. 7 Aggregation to Daily Level Daily Average Flight Time (DAFT) is the mean daily EFT of all arrivals from a particular origin. Daily Flight Time Index (DFTI) is a weighted average of the DAFT for a fixed market basket of origins. Like EFT, DAFT and DFTI can be decomposed into departure delay, taxi time, and airborne time. 8 4
DFTI Before and After Capacity Expansion DFTI 25. 2. 15. 1. 5.. 1/1/95 4/1/95 7/1/95 Before 1/1/95 1/1/96 4/1/96 7/1/96 Date 1/1/96 1/1/97 After 4/1/97 7/1/97 1/1/97 1/1/98 No obvious impact for good days. Some indication of decrease in bad days. Some very bad days both before and after. 9 Daily Level DFTI Model Statistical model estimated on daily observations of DFTI at DFW and explanatory variables. Explanatory variables include: Demand Weather Delay at Origin Airports Expansion 1 5
Metrics for Explanatory Variables Explanator Demand Weather Origin airport delay Capacity Expansion Metric Hypothetical deterministic delay based on scheduled arrival times and nominal capacity. Four weather factors resulting from performing factor analysis on 15 weather variables. Factors correspond to temperature, wind, precipitation, and visibility. Average departure delay for flights not going to DFW region from origin airports included in market basket. Dummy variable = prior to 1/1/96 and 1 after 1/31/96. 11 Predicted vs Actual DFTI Actual DFTI 24. 22. 2. 18. 16. 14. 14. 16. 18. 2. 22. Predicted DFTI Model accounts for most variation in DFTI. Pronounced heteroskedasticity poses estimation problems. 12 6
Effect of Capacity Expansion on DFTI Strong interaction with visibility factor. After expansion, impact of low visibility on DFTI is essentially eliminated. No other significant effects. 13 Day-to-Day Variation in Impact Frequency Cumulative Frequency 15 1 5-1 -9-8 -7-6 -5-4 -3-2 -1 1 2 3 DFTI Difference 6 5 4 3 2 1-1 -9-8 -7-6 -5-4 -3-2 -1 1 2 3 DFTI Difference Less than 1 minute reduction on 6 percent of days. Greater than 4 minute reduction on 1 percent of days. Largest reductions of 1 minutes. Slight increase on about 25 percent of days. 14 7
DFTI Impact vs DFTI Value Expected Reduction of DFTI 15 1 5 14. 15. 16. 17. 18. 19. 2. 21. -5 Expected DFTI without Expansion Greatest estimated reductions on days with greatest estimated delays. Implies increase in reliability. May also have masked benefit since bad days are still bad. 15 Effect of Capacity Expansion on DFTI Components 1.5 -.5-1 -1.5-2 -2.5.75-1.88 -.21 AIRBORNE TIME TAXI TIME DEPARTURE DELAY Sizable reduction in departure delay due to reduced ground holding. Increase in taxi time due to distance of runway from terminal. Small reduction in airborne time. 16 8
Sources and Components of DFTI Change from Before to After Expansion Source Departure Taxi Airborne TOTAL Delay Time Time CONTRIBUTION Demand.771.3679 3.432 3.8482 Origin Airport.317.43 -.1437 -.177 Delay Total Weather.1672 -.1188 -.285 -.2321 Origin Airport Delay-Weather Interactions Capacity Expansion TOTAL CHANGE.228.827.341.3196-1.881.7549 -.291-1.3353-1.422 1.91 2.84 2.4927 17 Airline Adaptation Metrics Number of Operations Peaking Concentration Scheduled Layover Times 18 9
Airline Departures from DFW Operations Departures from DFW 12 1 8 6 4 2 94,1 94,3 95,1 95,3 96,1 96,3 97,1 97,3 Quarter TOT AA+DL EV+MQ Others No significant increase after expansion. Remains 1 percent below preexpansion highs. No change in AA/DL dominance. 19 Schedule Peaking Find shortest time interval in which given number of operations are scheduled (5 operations in this case). Convert to equivalent operations per hour. Performed for arrivals, departures and both. 2 1
Schedule Peaking Results (AA Only) Operations 35 3 25 2 15 1 5 1,96 7,96 1,97 7,97 1,98 Time "Peak-hour" Operations D A Both Arrival peaking stable. Departure peaking decreases. Combined peaking increases. Reduced gap between departure and subsequent arrival banks. 21 AA Cumulative Arrival and Departures--Jan 96 and Jan 98 January 1996 operation January 1998 operation 6 6 5 5 operation 4 3 2 Operation 4 3 2 A D 1 1 5 1 15 2 time 5 1 15 2 time 22 11
Hypothetical Deterministic Delay (HDD) HDD cumulative number 25 2 15 1 5 demand capacity area = total delay 8 1 12 14 16 time Combined measure of banking intensity and duration Based on hypothetical delay as a function of flight schedule assumed capacity level (9 operations per hour in this case) Delay calculated from input-output diagram 23 Trends in HDD Smoothed HDD 3.5 3. 2.5 2. 1.5 1..5. Jan-95 Apr-95 Before Jul-95 Oct-95 Jan-96 Apr-96 Jul-96 Oct-96 Date Jan-97 After Apr-97 Jul-97 Oct-97 Jan-98 Sharp jump in summer 1996. Further increase after expansion. Impact of expansion is uncertain Large values in early 1995. Fluctuations after expansion. Role of confounding factors (pilots union). 24 12
Total Impact of Expansion on Fight Time Assumed Impact on Demand Direct DFTI Impact Indirect DFTI Impact Total Impact None -1.39-1.39 Comparison with July- Sep,1996-1.39.51 -.88 Comparison with April- June,1996-1.39 1.78.39 Direct delay reduction offset by Induced change in demand (HDD). Degree of induced change uncertain. Under most plausible assumption, airlines traded in about 4 percent of direct reduction for schedule modifications. 25 Conclusion Expansion reduced delay, all else equal, about 1.3 min/flight. Most reduction on bad weather days. Some (~4 percent) of delay reduction apparently traded for schedule changes. Adaptations may have increased or decreased benefit. 26 13