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 ► 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)

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

Scenario 1 Scenario 2

5 Time Periods AM PeakPM Peak MiddayEveningNighttime Puget Sound Trends,

Travel Demand Modeling GENERATION DISTRIBUTION MODE CHOICE ASSIGNMENT Assign trip tables to networks

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

SECONDARY TASKS ► Results Outside the Model  Trip Diversion by Time  Trip Deterrence  Bridge Restoration Costs and Period  Traffic Mitigation Measures

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)

Tab. 1: Aggregate Daily Travel Times by Mode, Time of Day, and Scenario (Hours) SOVCP2CP3+VanL TruckM TruckH Truck Total TT/Day Night112,47815,4584,258 -8,0802,1491,197143,619 Night 1121,02016,6094,555 -8,4072,2701,283154,145 Night 2122,47016,8034,603 -8,5262,3081,305156,014 AM268,98739,12013, ,32210,4536,122360,975 AM 1295,75642,34314, ,44111,7547,018396,111 AM 2349,76852,57218, ,69911,7117,051466,799 Midday394,250112,19434, ,49024,55714,588623,063 Midday 1433,382122,59537, ,85527,07216,403683,116 Midday 2438,954124,17938, ,57827,56316,711692,265 PM504,966119,42340, ,92214,1508,155720,798 PM 1578,418135,13145, ,33616,4559,685822,976 PM 2592,389138,14946, ,48516,98910,012842,916 Evening176,26658,49120, ,3253,0901,397273,046 Evening 1188,47062,35421, ,1383,3401,535291,593 Evening 2190,32962,95121, ,3323,3951,564294,524

Comments on Table 1 ► Baseline total travel time = 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.

Tab. 2: SOV Regionwide Average Travel Times by Time of Day and Scenario (mins) NightAM PeakMiddayPM PeakEvening Baseline Scenario Scenario

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)

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])

Tab. 3: Value of Daily Travel Time for All Modes (Lower Range: $ ) NightAM PeakMiddayPM PeakEveningDaily Sum Baseline1,365,8454,148,3108,450,1497,863,9572,811,22624,639,488 Scen. 11,462,8364,588,0009,299,2459,009,9263,006,63527,366,641 Scen. 21,481,7395,173,1989,440,4689,242,5203,039,17828,377,104

Tab. 4: Value of Daily Travel Time for All Modes (Upper Range: $ ) NightAM PeakMiddayPM PeakEveningDaily Sum Baseline 2,438,989 6,833,121 13,475,143 13,759,204 5,229,894 41,736,351 Scen. 1 2,614,772 7,518,877 14,794,433 15,713,385 5,586,721 46,228,188 Scen. 2 2,647,391 8,690,167 15,006,993 16,102,786 5,644,471 48,091,808

Tab. 5: Comparison between Lower and Higher Values of Travel Time Lower Value ($ )Higher Value ($ ) Daily Sum Reconstruction PeriodDaily Sum Reconstruction Period Baseline 24,639,488 4,435,107,753 41,736,351 7,512,543,142 Scenario 1 27,366,641 4,925,995,338 46,228,188 8,321,073,824 Scenario 2 28,377,104 5,107,878,781 48,091,808 8,656,525,359

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 $ m. (Sc. 2)

Tab. 6: Changes in Commute Times on Selected Disrupted Routes (mins) AMPM BaselineScen. 1Scen. 2BaselineScen. 1Scen. 2 Bellevue-Downtown Downtown-Bellevue Redmond-Downtown Downtown-Redmond Renton- Downtown Downtown-Renton UW-SeaTac Airport SeaTac Airport-UW

+ +8 SeaTac UW Renton AM Peak Commute Time Differences Baseline vs. Scenario 2

UW SeaTac Renton PM Peak Commute Time Differences Baseline vs. Scenario 2

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. AM: 54 mins. vs. 22 mins. PM: 90 mins. vs. 30 mins. PM: 90 mins. vs. 30 mins.

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

Times From Microsoft HQ, Scenario 1 (PM Peak)

Travel Times From Microsoft HQ, Scenario 2 (PM)

MAP COMPARISONS ► Compares Scenarios 2 and 1 with Baseline using Microsoft HQ as a base point ► Trips, <10 mins. in Redmond, mins. in to other Eastside cities, mins. reach other Eastside cities, mins. reach City of Seattle, 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 or 90+ mins.

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

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

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?

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

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

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

Next Steps

Travel Demand Modeling GENERATION Productions and Attractions from population and employment DISTRIBUTION Connect Productions to Attractions MODE CHOICE Split into Modes ASSIGNMENT Assign trip tables to networks

TIME (1,000 hours) VMT (1,000 miles) 2000 Base 2,46877,710 No bridges 2,71480,712 No B + No I-5 2,75680,696 No bridges (full run) 2,45076,501 No B + No I-5 (full run) 2,45976,078 Summary Statistics

Map of Sub-areas

Sub-area Example Home-Based Work Trips Entire Region Bellevue to Seattle CBD Trips % Transit Trips Assignment Only 2,377,7367.5%8, % Scenario 1 with feedback 2,377,7367.6%2, % Scenario 2 with feedback 2,377,7367.6%2, %

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

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

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