WHEN PT

EisenhowereralHighwaySystemlegis-

lation in 1956,he couldn’tpossibly have envisioned

thebehemothconstructionprojectthatis now beingundertakenin Bostonto

completethe system.Governmentoffi-cials call it the CentralArtery/Tunnel(CA/T) Project;locals just say“the BigDig.” By thetimeit’s finishedin 2004,thisroadwaywill boast a segmenteight

laneswide, 3.5 miles long, completelyburiedbeneaththebustlingfinancialdis-trict of oneof the nation’soldestcities.The new tunnel will replaceBoston’smuch-malignedCentralArtery—adilap-idatedsteelviaduct that cutsbetween

downtownhigh-rises—withastretchoftheworld’s largestundergroundhighway.An underwatertunnel (completed in1995)will feedtraffic from theairportinto the artery,all for theunprecedent-ed costof more than $10billion.

Although burying the highwaypromisesto leavean improved envi-

ronmentfor Boston’ssurfacedwellers—cleaner,quieter,more open—it raisesthestakesfor subterraneantravelers.Traffic jams and flat tires, merelyannoyingaboveground,canturn dead-ly below if motoristsaretrappedin ahazeof toxic exhaustfumes.Add to the ~mix acarfire or anoil tankerexplosionandthesituationcouldbecomedire. So

Fed up withnotoriously badtraffic and thepollution andnoise that gowith it, Boston ishiding its highwaysunderground—butwhat will it take tokeep subterraneantravelers safe?BY SIMSON L. GARFINKEL

Big Dig engineersare pioneering new

technologiesin construction,trafficman-agement,andfire control,all designedtokeep life flowing smoothly and safely

throughtheartery.

BEYOND LAYING 5TEEL AND POURING CON-

crete,Big Dig crewsaredeployinghundreds

of closed-circuittelevisioncam-eras,infraredsensors,andvari-able messagesigns throughout

the system,wiring it togetherwith a computer system thatcanwithstandaterroristattack,andbuilding acommandcenterso filled with screens,keyboards,and projection devices that it

wouldmakeDarthVadergreenwith envy.It’s all partof the CentralArtery/Tunnel“Smart Highway,” or Intelligent Trans-portationSystem.

Working in the“Star Wars” control

center, the CA/T’s half-dozen humanoperatorswill strive to maximize trafficflow andminimize motorists’exposureto

carbonmonoxide.Thetools at their dis-posalwill includetraffic lights, speedlimitsigns,lane closuresignals, AM andFMradiotransmitters,ventilationequipment,evensewagepumps.

TheCA/T’s computerswill constant-ly monitortheflow of traffic throughthesystem.If thereis asuddeninterruption—saythetraffic in alanedropsfrom 60 to 5mph—the computerwill automatically

swingacamerato pointattheareain ques-tion. The computer can calculate theseverity of the incident, designateanappropriatehumanoperatorto handleit

(basedon his orher trainingandcurrent

PHOTOGRAPHS BY ANDY RYAN

UNDER Co NTR 01: A computer simulation can model common traffic situations. In the firstpanel, a car has just broken down ~nthe tunnel (indicated by a red square in the top center). In the sec-ond, operators respond by closing lanes (yellow Xs) and the entrance to the tunnel (red line).The CA/Tmanagers’ goal is to have the incident cleared and traffic flow restored in a mere 15 minutes (last panel).

66 TECHNOLOGY REVIEW May/June 199S

assignments),andmakethevideoimageappearat theoperator’sconsole.Thenthecomputerwill recommendastrate-

gy for handlingthesituation,but leavethefinal decisionto thehuman,who canchangelights,adjustventilationequip-

ment,or sendmessagesto drivers,all to

preventa minor fender-benderfrombecomingamajor catastrophe.

But whatshould anoperatoractu-

ally do in an emergency?Closelanes?

Slowtraffic?Diverttraffic?Andhowlongshouldlanesstayclosed?Toanswerthesequestions,theMassachusettsHighwayDepartmentcontracted with MIT’sIntelligentTransportationSystemsgroup(http://its.mit.edu/) to build an

advancedcomputersimulation thatmodels up to 10,000vehicles movingthroughrampsandtunnels.

“We simulatethedrivers’decisionssuchasacceleration,deceleration,lane-changing,merging,andyielding,” saysprofessorMosheBen-Akiva,who directsthe MIT group.“We cansimulatemci-

COMPOUND EYE: Operators in the “Star Wars” control center (above) can see every inch of the

CA/T system. Along the highway 500 cameras feed images to a wall of monitors; when the computerdetects a problem, it switches the video image to an operator’s desktop monitor.The operator can alertdrivers to lane closings and speed limit changes using variable message signs (below).

TECHNOLOGY REVIEW May/June 1998 67

dentsby blocking lanes for a certainduration. We cansimulate changesinvisibility conditions.”The system canevendeterminetheeffectof closingexitsor addingnewones.

Along with thetrafficsimulator,theMIT grouphasbuilt asecondsimulatorthatmodelstheGA/T’s humanoperatorsandtraffic managementsystem.This letstheresearchersseetheeffectthatdiffer-ent traffic managementstrategieswillhaveontheebbandflow oftraffic insidethe tunnel. When thereis an accidentinsidethetunnel,for example,thepor-tal lightson thefreewayimmediatelyturnfrom greento redto preventmorecars

from entering.Using the simulator, theresearcherscalculatedhow long theoper-ators should wait after the accident isclearedbeforetheportallights areturnedfromredbackto green.“Theoriginalplansto changetheportallights to greenimme-diately was not a good idea,” says Ben-Akiva. “You should delaythechangeuntilyoulet the traffic insideclearout. Other-wise, you generateshockwavesof trafficinsidethetunnel.”

FirA in ~L, ~

IF cA/T DESIGNERS AND OPERATORS GOT

somesurpriseswhentheybegansimulatingtraffic flow, they got evenbigger shockswhentheybeganto look into anotherprob-lem: howto protectatunnelandits occu-pantsfromtheravagesof fire. Itwasn’tjustthe threatof direct burnsthat theywereworriedabout.In fact,“Smokeandheatarethe real killers in afire$’ says RichardW.

Drake,operationsmanagerfor theCentralArtery/TunnelProject.

For years,explainsDrake, engineersaroundtheworldhavebeenbuilding auto-

mobile tunnelswith ventilationequipmentlargeenoughto handlethesmokefromthe

biggestfire conceivable.But theyhadnowayof knowinghowtheir conceptionsoffire wouldmatcharealblaze.Thoughtun-

nel fires—suchasthe onethatbrokeoutin 1996 in theChannelTunnelthatcon-nectstheU.K. andFrance—captureinter-nationalmediaattention,nonehasburned

FANNING THE FLAMES: Shouldfirebreak Out underground, motorists’ lives will

depend upon seven mammoth ventilationbuildings perched above the tunnel. Eachstructure will house 18-foot fans that drawfresh air in through the louvered sides of thebuilding and pull smoke and fumes out of thetunnel. A series of experimental fires in anabandoned tunnel in West Virginia taught BigDig engineers how best to operate fans duringa blaze, allowing occupants to breathe withoutfeeding the flames.

underthewatchfuleyeof high-speedsclentific instruments.So engineersha~ ‘t

alwaysbasedtheir fireproofingdesignso rtheoreticalmodels,not harddata.

Uncomfortablewith this uncertainty.engineershavefor decadesover-built the: iiprojects,addingmore ventilationequipment, insulation,andstructuralsuppoirithantheythoughtnecessary—justin casttheirmodelsunderestimatedtheheatan dsmokeatunnelfire couldproduce.

What engineersneededwas a te~ ~i

bed—anexperimentalsystemfor tunnifires. And in the early 1980s,theFederaHighwayAdministration (FHA)cameuFwith one,re-routingasectionof 174 inwaythat leftanempty 1.1-miletunneli rthehills of WestVirginia. TheretheFH.Ateamedup with ParsonsBrinckerhoff,or Lt

of Big Dig’s primarycontractors,to peiform aseriesof full-scaleburnsthatwoul cfinally put thetheoriesabouttunnelfirtto the test.

The teamspent$10million renovaingtheabandonedtunnelwith astate-o:f.the-artventilationsystemandanother$1

ARTERIAL BYPASS: BigDigcontrac-tors are tearing down the elevated artery(above) and tearing up the urban landscape(below) to make way the new tunnel.

68 TECHNOLOGY EEVIEW May/JunE 1998

million installingsophisticatedmonitor-inginstruments.“We outfittedthetunnelon agridsystemsoyou couldcollectdata

on temperature,air flow, and carbonmonoxide throughout the tunnel,” saysDrake,who supervisedtheproject.

In themiddleof theabandonedtunneltheengineersbuilt largesteelpansmeasur-ing morethan 10 feeton aside.Theyfilled

thepanswith 6 inchesof water(to protectthesteelfromtheheat)andthenaninch offuel oil. A remote-controlledpropaneburn-

erignitedthefuel.Ultimately,Drakesupervised101 burns.

Thesmallestwas10 megawatts(MW),sim-

ulating asmallcarburstinginto flames.Thelargestwas 100 MW—approximatelythepower releasedwhen a small gasoline

tankerhasahead-oncollisionwith atruck.“If youwantto seewhatHell lookslike,

we’ll showyou apictureof a100-megawattfire,” saysDrake.“It is absolutelyastounding

(A~>seetiles blown off thewall. Theasphalt~dtarexpansionjointsbubble.”

To theteam’samazement,the tunnelandtheventilationequipmentheldup far

betterthroughtheseholocauststhanthemodelshadpredicted.“Nobodythoughtwewouldevergetthis numberoffiresoff. They

thought the tunnel would collapse longbeforewe were donewith iC’ saysDrake.

Theresilienceof thetunnelinWestVir-

ginia pointedtowardastaggeringconclu-sion:Worldwide,billions of dollarshadbeenwastedmakingtunnelsmorefire resistant

thanwaseverneeded.Although theresultscametoo lateto

allow for a completeBig Dig redesign,Drakehasstill beenableto savetensof mil-lionsof dollarsin concreteandexcavationcostsby shrinkingsomeventilationshaftsandeliminatingothers.“We savedabout$25million on this projectin insulationcosts alone,” says Drake.

“We areveryconfidentthatwe canshowyou $45 mil-lion in savingsoverall.”

More important, thetestshavetaughtengineershow to “tune” the CA/T’sventilation system. In the

eventof a fire, saysDrake,

555

ill

conventionalwisdomhadalwaysheldthat fanssupplyingfreshair to tunnelregionsadjacentto theflamesshouldbesetatroughly50 percentof capacity.Itwasanattemptto strikeadelicatebal-ance:“You don’twant to feedfreshair”to thefire,explainsDrake,butyou don’twantpeopletrappedin theircarsto suf-focateeither.

Again, conventionalwisdom waswrong. TheWestVirginia experimentsshowedthat it is betterto turnthenear-by supplyfanswaydown duringafire—to just 10 percentor 20percentof capac-ity. At thesereducedsettings,thetestsprove,theventilation system will stillprovide enoughfresh air for trapped

motorists,andit won’t fanthe flames ashigh. It’s astrategicadjustmentthatmight seem minor, butwith aquarterof amillionvehiclesexpectedto nego-

tiate the tunnel eachdayby 2010,its impactcouldproveenormous. Ii~

DIAGRAM BY DOUG STERN PHOTOGRAPHS BY ANDY RYAN TECHNOLOGY REVIEW May/June 1991 69