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THE TRANSPORTATION IMPLICATIONS OF A TERRORIST ATTACK ON SEATTLE’S HIGHWAY NETWORK

THE TRANSPORTATION IMPLICATIONS OF A TERRORIST ATTACK ON SEATTLE’S HIGHWAY NETWORK. Chang-Hee Christine Bae (University of Washington) Larry Blain (Puget Sound Regional Council) and Alon Bassok (University of Washington). INTRODUCTION.

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THE TRANSPORTATION IMPLICATIONS OF A TERRORIST ATTACK ON SEATTLE’S HIGHWAY NETWORK

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  1. THE TRANSPORTATION IMPLICATIONS OF A TERRORIST ATTACK ON SEATTLE’S HIGHWAY NETWORK Chang-Hee Christine Bae (University of Washington) Larry Blain (Puget Sound Regional Council) and Alon Bassok (University of Washington)

  2. INTRODUCTION • Primary aim is to model the impacts on travel of a feasible terrorist attack on Seattle’s transportation network • The unique topography of the Puget Sound Region implies that a few pinpointed attacks can have major consequences • We explore taking down the 2 bridges (I-90 and SR520; Scenario 1) and adding an attack on I-5 under the Convention Center (Scenario 2)

  3. CHARACTERISTICS • Employment structure dominated by Downtown Seattle and Eastside subcenters (Bellevue and Redmond) separated by Lake Washington • Other than circuitous trips around the lake, there are only the two bridge links • I-5, running through downtown Seattle, links Canada with San Diego

  4. Scenario 1 Scenario 2

  5. http://www.wsdot.wa.gov/PugetSoundTraffic/

  6. 5 Time Periods AM Peak PM Peak Nighttime Midday Evening Puget Sound Trends, 1997 <http://www.psrc.org/datapubs/pubs/trends/t6trend.htm> http://www.wsdot.wa.gov/PugetSoundTraffic/

  7. Travel Demand Modeling

  8. PRIMARY TASKS • Estimate travel time losses (and related $ costs) associated with Scenario 1 and 2, essentially route diversion costs • Examining how modal shifts might mitigate the additional congestion of Scenarios 1 and 2 (in progress) • Estimating the freight delay contribution to business interruption

  9. SECONDARY TASKS • Results Outside the Model • Trip Diversion by Time • Trip Deterrence • Bridge Restoration Costs and Period • Traffic Mitigation Measures

  10. TRIP DIVERSION AND COSTS • With the 2 bridges down, tripmakers have to go around Lake Washington either by the northern or the southern routes • In Scenario 2, vehicles can either download from I-5 to surface streets downtown or (if through Puget Sound traffic) divert to the alternative freeway (I-405)

  11. Tab. 1: Aggregate Daily Travel Times by Mode, Time of Day, and Scenario (Hours)

  12. Comments on Table 1 • Baseline total travel time = 2.122 m. hours • Increase in total travel time by 226,200 hours (10.7%) in Scenario 1 • Increase by 330,800 (15.6%) in Scenario 2 • Implication: Bringing the bridges down increases congestion and travel times more than the I-5 blockage • Much denser flows in PM than AM peak, but the event raises travel times by proportionately more AM than PM • SOVs (as expected) dominate traffic flows (about 4/5ths of total travel time) • “Midday” (9 a.m.-3 p.m.) traffic flows quite high, possibly the result of “peak lengthening” of the morning peak towards 10 a.m.

  13. Tab. 2: SOV Regionwide Average Travel Times by Time of Day and Scenario(mins)

  14. Comments on Table 2 • Increase in regional average travel times consistently higher in the PM than the AM peak (27% in the Baseline) • Offpeak changes milder than peak changes, as expected • Nighttime trips longer (longer trip lengths?) • Travel times shorter than some other sources (but Census deals only with the generally longer worktrips)

  15. TRAVEL TIME VALUES • Important component of economic costs of this type of terrorist attack • Research on value of travel time varies widely (20-50% of wage rate). The % also varies with income and type of trip • Two personal values ($6.50 and $13.00 per hour and commercial value of $35 per PCE-hour [the same as in the LA ports study])

  16. Tab. 3: Value of Daily Travel Time for All Modes (Lower Range: $ )

  17. Tab. 4: Value of Daily Travel Time for All Modes (Upper Range: $ )

  18. Tab. 5: Comparison between Lower and Higher Values of Travel Time

  19. TRAVEL TIME LOSSES • Daily losses in Sc. 1 = $2.73m.,Sc. 2 = $3.74m. lower end ($4.49m., $6.36m. Upper end). Increase over Baseline = 11% (Sc. 1) and 15% (Sc. 2) • Total losses (180-day assumption): Lower end, $490.9m (Sc. 1) and $672.8 m. (Sc. 2); Upper end, $808.5m. (Sc. 1) and $1.144.0m. (Sc. 2)

  20. Tab. 6: Changes in Commute Times on Selected Disrupted Routes (mins)

  21. AM Peak Commute Time Differences Baseline vs. Scenario 2 UW +30 + +29 +11 +8 SeaTac Renton

  22. PM Peak Commute Time Differences Baseline vs. Scenario 2 UW +54.7 +59.6 +7 +14.9 Renton SeaTac

  23. Travel Times on Individual Routes • Most extreme case: O/Ds near the SR520 Bridge (e.g. Downtowns Bellevue and Seattle) AM: 54 mins. vs. 22 mins. PM: 90 mins. vs. 30 mins.

  24. Travel Times From Microsoft HQ, Baseline (PM Peak)

  25. Times From Microsoft HQ, Scenario 1 (PM Peak)

  26. Travel Times From Microsoft HQ, Scenario 2 (PM)

  27. MAP COMPARISONS • Compares Scenarios 2 and 1 with Baseline using Microsoft HQ as a base point • Trips , <10 mins. in Redmond, 10-20 mins. in to other Eastside cities, 20-30 mins. reach other Eastside cities, 30-40 mins. reach City of Seattle, 40-60 mins. to other West of lake locations • In Scenarios 1 and 2, little difference on the Eastside, but travel times to Seattle and other west of lake locations increase to 80-90 or 90+ mins.

  28. MODAL SHIFTS • 2.5% of trips are by transit. Total equivalent to current tripmakers across the bridges. • With certain assumptions, we can estimate shifts to buses (work in progress) • Carpool shares (19% in AM peak and 25% in PM peak) already high. How far they can be increased (even in a short-run situation) is questionable

  29. FREIGHT DELAYS AND BUSINESS INTERRUPTION • Not so severe because most freight trips are North-South rather than cross-lake. Also, trips originating outside the region can take I-405 even if I-5 is blocked. Hence, freight delays increase by 12.6% in Scenario 1 over the Baseline but only by another 2.1% in Scenario 2 • Our model estimates of business interruption because of freight delays are $201m. • Additional commuting costs will fall on labor rather than business

  30. TRIP DIVERSION BY TIME • Many non-worktrips (77% of total trips) take place in the peaks • Can these be diverted to off-peak? Problem is 9 a.m.-3 p.m. already has heavy traffic • Scope for diversion greatest in the evening and nighttime. Can freight traffic be diverted?

  31. TRIP DETERRENCE • 228,000 trips daily across the two bridges • Little evidence to suggest how many could be deterred • Most non-work trips could either be deterred or diverted to destinations on the origin side of the lake • However, non-work cross-bridge share much lower than regional average • Even if 5% of cross-bridge travel could be diverted, it could make a difference to congestion in Scenarios 1 and 2

  32. RESTORATION PERIOD AND COSTS • This discussion is speculative because much depends on the extent of the damage • We assume a restoration period of 180 days, based on experience elsewhere and the record of political and institutional delays in Washington • Bridge reconstruction and I-5 clearance costs are speculative. Our best guess is $200 million

  33. TRAFFIC MITIGATION MEASURES • $ costs of a plan very small relative to economic costs of additional travel time • Introduce traffic flow improvements on the around the lake routes • Promote more carpool use via public education, incentives and/or mandates • Induce a modal shift to buses via new routes, increasing service frequency and perhaps free fares • Facilitate trip diversion by time, e.g. flextime, compressed work weeks

  34. Next Steps

  35. Travel Demand Modeling

  36. Summary Statistics

  37. Map of Sub-areas

  38. Sub-area Example

  39. CONCLUSIONS • We evaluated the transportation implications of bombing two bridges on I-90 and SR520 (Scenario 1), then added blocking I-5 under the downtown Convention Center • Travel times increased by 10.7% in scenario 1 and 15.6% in Scenario 2

  40. CONCLUSIONS (cont.) • As expected, travel times increase more in the peaks, especially the AM peak (although volumes are larger in the PM peak) • The upper end value of extra travel costs are $809m. in Scenario 1 and $1,144m. in Scenario 2. This helps to evaluate the resources to be devoted to prevention and mitigation

  41. CONCLUSIONS (cont.) • Individual tripmakers close to the bridges incur a high cost, up to 2.3x more in the AM peak and 3x more in the PM peak • Freight delays add $201m. • Estimate of infrastructure reconstruction: $200m. • Traffic mitigation plans could be helpful, but would need to be prepared well in advance

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