Boston Tunnel Report, Oct. 1, 2010

8/8/2019 Boston Tunnel Report, Oct. 1, 2010

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REDESIGN OF THE BOSTON

TUNNEL GUARDRAILby

Daniel Albuquerque, M.S.C.E.Graduate Research [email protected]

Eric Jowza, B.S.C.E., E.I.T.Graduate Research Assistant

[email protected]

Kevin Schrum, B.S.C.E., E.I.T.

Graduate Research [email protected]

Ryan Terpsma, B.S.M.E., E.I.T.Graduate Research [email protected]

Ben Dickey, B.S.C.E., E.I.T.Graduate Research [email protected]

Jennifer Schmidt, M.S.C.E., E.I.T.Graduate Research [email protected]

Cody Stolle, M.S.M.E., E.I.T.

Graduate Research [email protected]

Midwest Roadside Safety Facility2200 Vine Street

130 Whittier BuildingUniversity of Nebraska-Lincoln

Lincoln, NE 68583-0853

Presented to

Massachusetts Turnpike AuthorityMassachusetts Turnpike Interchange 14

Weston, MA 02493

and

Massachusetts Department of Transportation10 Park Plaza, Suite 3170

Boston, MA 02116

August 20, 2010


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ABSTRACT

The Boston Tunnel pedestrian rail design was analyzed and three modifications to the

current design were proposed: (1) relocation of the existing barrier with the addition of chain

link fencing; (2) retrofit of the existing rail with folded plate sections; and

(3) replacement of the rail with a crashworthy, flexible chain link fence. Rail redesign is

contingent on three critical observations: (1) increased rail offset from the concrete barrier will

result in less motor-vehicle occupant contact, snag, and propensity for a motorcyclist to flail into

the barrier; (2) limiting the occupants or motorcyclist's ability to contact the thin plate posts will

decrease the associated hazard; and (3) "softer" and more flexible systems will allow

motorcyclists to slow more gradually and not suffer high accelerations or large forces, which

contribute to injury and fatality. It is expected that the implementation of one of the designs

recommended in this report, or a modification thereof, will significantly increase safety

performance of the rail and save lives, in addition to reducing potential liability to the State of

Massachusetts.

1INTRODUCTIONPedestrian rails are designed to prevent pedestrians from accidentally departing a

pedestrian structure into a potentially hazardous location. When pedestrian rails are mounted on

top of crash barriers, the existing combination rail must have a unique set of qualities: it must be

aesthetic, crashworthy, and appropriately service the needs and provide protection for a

pedestrian. Many times, urban roadways in tunnels or on bridges may implement pedestrian rail

combinations with traffic barriers to more efficiently utilize available space, although these

pedestrian combination barriers commonly service only maintenance or rescue personnel. The


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pedestrian rail on an elevated platform utilized in the Boston Tunnel is one such example of a

combination guardrail.

The Boston Tunnel rail design consisted of rectangular 2-in. wide x -in. thick (60-mm

x 19-mm) steel plate posts welded to pentagonal baseplates, with 2-in. (51-mm) diameter

schedule 40 SST pipes for horizontal members. The pipes were welded to the posts at nominal

mounting heights of 28 and 41 in. (711 and 1,041 mm) from the pedestrian walkway. The flat

plate posts were welded to chamfered base plates, which were epoxied with 6-in. (152-mm) studs

to the top of a 32-in. (813 mm) high safety-shaped concrete barrier. This barrier design is shown

in Figure 1.

This guardrail has been installed in the Boston Tunnel since its partial completion in

2003. Since that time, seven people have died due to crashes with the guardrail, four of which

were motorcyclists and three of which were passengers in vehicles who became entangled in the

rail [1]. Fatalities associated with rail designs result in costly litigation suits, re-evaluation

studies, negative public perception, blockage of major arterials caused both by the accident itself

and the responding crews, and most importantly, loss of human life. Critical analysis of the

guardrail with potential redesigns or retrofits is paramount to improving Boston's way of life.


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Figure 1. Existing Rail Design, Boston Tunnel


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2LITERATURE REVIEWResearchers at Virginia Tech University undertook a concerted effort to evaluate

motorcyclist safety when impacting roadside guardrails commonly used to protect occupants of

motor vehicles [2]. Gabler evaluated motorcyclist fatality rates for various guardrail systems

installed on the sides of the road and concluded that most guardrails were not designed for

motorcyclist impact. Gabler further determined that there was a 12.4% motorcyclist fatality rate

when a motorcyclist impacts existing crash barriers, compared with a motor-vehicle fatality rate

of 0.15%. As a result, motorcyclists are more than 82 times more likely to be killed during a

crash with a guardrail system than operators of passenger vehicles. However, since

motorcyclists are under-represented in total vehicle registrations and traffic volume, barriers are

typically not designed to protect both motorcyclists and occupants of passenger vehicles.

The American Association of State Highway and Transportation Officials (AASHTO)

Guide Specifications for Bridge Railings set forth the minimum specifications for pedestrian

guardrails and provided the first crash-testing standards for combination pedestrian and traffic

guardrails [3]. Pedestrian rails should be 42 in. (1,067 mm) above the walkway. The minimum

clear spacing is 15 in. (381 mm) for horizontal elements and 8 in. (203 mm) for vertical

elements. Chain link fence is exempt from the rail spacing requirements. The strength

requirement for a pedestrian rail is 50 lb per linear foot (730N per linear meter), transverse and

vertical combination load. For combination guardrails, full-scale vehicle crash tests were

conducted according to performance level (PL) guidelines.

The National Cooperative Highway Research Program (NCHRP) is an organization

which provides federal research money for the safety improvement of roadways in the United

States. NCHRP provided funds to investigate appropriate impact testing conditions and


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crashworthiness criteria for evaluation of roadside features in NCHRP Report 350 [4]. This

report set a precedent for many types of roadside safety components, including bridge rails,

which had previously been tested according to the AASHTO performance level guidelines [3].

More recently, an update to the criteria in NCHRP Report 350, entitled theManual for Assessing

Safety Hardware (MASH), was accepted by the AASHTO, which redefined test impact criteria,

test vehicles, and acceptable safety performance criteria for evaluating roadside structures [5].

A combination traffic/bicycle bridge rail was developed to meet Test Level 4 of NCHRP

Report 350. The bridge rail consisted of a 31-in. (810-mm) high New Jersey safety shape

concrete barrier with steel rail panels attached to the back of the concrete barrier [6]. The steel

rail extended 22 in. (572 mm) above the concrete barrier and consisted of vertical spindles

spanning in between two horizontal steel tubes. It had a successful performance for a 17,637-lb

(8,000-kg) single-unit truck impact at 50 mph (80 km/h) and at 15 degrees and a 4,409-lb (2,000-

kg) pickup truck impact at 62 mph (100 km/h) and at 25 degrees.

A double-tube pedestrian/bicycle rail mounted on a curb was developed to meet

Performance Level 1 of AASHTO guide specifications. The bridge rail consisted of four

horizontal steel tubes spanning in front of a combination of W6x25 (W152x37.2) and tube posts

[7]. The rail had a successful performance with an 1,800-lb (817-kg) small car impact at 50 mph

(80 km/h) and at 20 degrees.

A vandal protection fence was developed to meet Performance Level 2 of AASHTO

guide specifications by the Texas Transportation Institute (TTI). The rail consisted of 2-in. (51-

mm) diameter, 7.3-ft (2.2 m) long Schedule 40 pipe spaced at 10 ft (3.0 m) apart and clamped to

the back of a 32-in. (813-mm) high New Jersey safety shape barrier [7]. Other 2-in. (51-mm)

diameter, Schedule 40 pipe horizontal line rails were spaced vertically at 3 ft (0.9 m) apart, with


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km/h) impact with the Boston Tunnel pedestrian rail. The simulated crash was terminated 350

ms after impact, at which point the vehicle was redirected away from the rail and the potential

for snag, occupant impact with the rail, and vehicle instability was reduced.

Impact with one rail caused the rail to deflect both downstream and backward laterally,

and the posts caused the impacting fender to snag and tear. The Explorer model made contact

with the rail along the top of the occupant compartment. Although it is expected that smaller

vehicles will not be subject to as much occupant head-slap and ejection concerns in free-

wheeling vehicles, the "zone of intrusion" for impacting occupants to project part or all of the

head out of the impacting-side window, even at moderate speeds, was still applicable [9,10] The

acceptable window to prevent head injury requires that either the head be shielded from impact

or that all impacted objects be located 11 in. (279 mm) back from the face of the barrier. Else,

the occupant of a vehicle may make contact with the fixed-object outside of the vehicle.

Based on the results of the simulations, it was very likely that an occupant involved in a

high-angle crash, which is more highly likely to occur when the roadway is curved, would have

made contact with the barrier structure. Occupant impact with a fixed structure represents the

maximum risk to the impacting occupant, significantly increasing likelihood of serious injury or

fatality. These results are consistent with reports that occupants of impacting vehicles have been

forcibly removed from the vehicles on impact [1].

Furthermore, vehicle contact with the rail caused excessive rail deflection, contributing to

vehicle snag. The vehicle snagged in the simulation and the rail crushed the right-front corner,

obstructing occupant view with the hood and imparting large accelerations to the vehicle.

Besides large occupant ridedown decelerations, snag also contributes to vehicle spin-out from

the rail, which could endanger occupants in vehicles adjacent to the impacting vehicle and cause


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subsequent collisions. Snag phenomena in constricted areas, particularly locations with low

visibility, is highly undesirable and potentially hazardous, in addition to being a burden both to

other motorists on the roadway as well as emergency personnel who have to navigate to the

scene of the accident.

4GUARDRAIL RETROFIT MODIFICATIONSResearchers identified three possible methods of alleviating the hazard associated with

the current rail design. The first method consisted of decreasing the width of the walkway by

relocating the guardrail so that the front face of the posts is 11 in. (279 mm) back from the front

edge of the top of the concrete barrier, so it is out of the zone of intrusion. A second method was

designed to retrofit the existing rail with 8-in. (203-mm) wide folded plates to create a shield in

front of the pedestrian rail to prevent extremities from protruding between the posts, which has

led to significant occupant risk. The last method, which may prove to be the safest and most

aesthetic, is to remove the existing pedestrian rail and install a chain link fence with thin pipe-

type tubes. This design was based on a retrofit of a vandal protection fence evaluated by TTI [7].

4.1Relocate the RailThe least costly design modification is to relocate the existing rail so that the front face of

the posts is 11 in. (279 mm) from the front edge of the top of the concrete barrier. By doing this,

virtually all risk of occupant interaction with the posts in the current rail design are eliminated,

based on an analysis of occupant head ejections during crashes [9]. Relocation of the existing

rail will not require modification to the rail structure or shape, and will minimize the total cost of

the modification. The zone of intrusion of an occupant with head ejection during a crash event is

shown schematically in Figure 3.


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Figure 4. Relocation Design


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4.2Retrofit the RailThe retrofit option is most desirable if relocating the rail is impossible due to narrow

walkways or if the cost of relocation is greater than the cost of materials. Furthermore,

retrofitting the rail could provide adequate impact behavior for all impact types. This design

therefore consisted of a rail element spanning along the front of the barrier.

This design was inspired by the literature review of several motorcycle crash barriers that

are currently used along European roads and highways. However, the cause of motorcyclist

injuries, and thus methods of alleviating these injuries, is currently under considerable debate.

The European designs utilize smooth concrete surfaces or sheet metal to cover the entire zone of

intrusion for motorcyclists to prevent any chance of snagging on the components of the guardrail

[11,12]. The proposed retrofit to the Boston Tunnel combination rail design consists of attaching

three 8 in. wide x 16-gauge thick (203 mm x 1.50 mm) rolled steel folded plate beams along the

lower portion of the guardrail. Detailed drawings of the retrofit design are shown in Figure 5.

The longitudinal beams consist of 8CS2x059 (203CS50.8x1.5) C-sections, which are standard

American Iron and Steel Institute (AISI) cold-formed structural sections [13]. These beams are to

be continuous along the length of the guardrail and are attached by L-angles at each of the posts.

These longitudinal folded plate sections, along with the concrete barrier, provide a smooth

surface that is free of snag points. The three sections may be welded together to act as one

continuous barrier that reduces the chance of penetration into the guardrail posts.

The proposed retrofit design will prevent a motorcyclist from penetrating into the

guardrail, as well as provide adequate protection for other motorists. This design will not require

a complete overhaul of the system because it utilizes the existing guardrails for much of its

structural design. No new drilling or anchoring into the concrete barrier would be required.


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Figure 5. Retrofit Design


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However, this design was based on analytical calculations and has not been crash tested

according to federal crashworthiness evaluation criteria. In addition, the weld-on L-angle option

requires extensive field welding that is likely to be labor-intensive, whereas the bolt-on L-angle

design will require three holes to be drilled in each of the -in. (19-mm) thick plates. The

retrofit design was created for the practical purpose of maintaining the existing rail and

protecting motorcyclists and impacting occupants, which may incur a higher price than the

installation of the new recommended traffic barrier.

4.3Replace the Rail with Crashworthy GuardrailA practical method of optimizing the barrier for the design criteria is to remove the rail

entirely and replace it with a new, crashworthy design which is capable of withstanding impact

and safely redirecting motorcyclists with minimal injury or hazard. This design option

incorporates the benefits of relocation, since the rail will be removed and the new rail may be

installed as far from the front side of the concrete barrier as space allows. It also incorporates the

benefits of retrofitting, since contact with all elements of the new proposed barrier will be

smooth and intended to safely capture an impacting motorcyclist or vehicle occupant.

A chain link guardrail may used as a safety treatment for the Boston Tunnel. Installation

of chain link fence will prevent occupants of errant vehicles and motorcyclists from penetrating

through the rail and making direct contact on the post structures. It is inexpensive to install and

maintain and does not have any sharp edges in the design which couch seriously affect motorists.

This design is modified from a crashworthy vandal protection fence tested at TTI [7].

Construction details are shown in Figure 6.


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Figure 6. Replacement Design


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The proposed chain link pedestrian rail design consists of 2-in. (64-mm) diameter

schedule 40 pipes, measuring 42 in. (1,067 mm) tall and welded to 6.5-in. diameter x -in. thick

(165-mm x 10-mm) circular base plates. Four -in. diameter x 6-in. long (19-mm x 152-mm)

ASTM A449 bolts epoxied to the top of the concrete barrier are located on a 5-in. (127-mm)

diameter bolt circle in the base plates.

Longitudinal barrier strength will be provided by two 2-in. (51-mm) diameter Schedule

40 pipes measuring 10 ft (3.0 m) long, spanning between vertical posts. The top longitudinal rail

is located at the top of the barrier, and the lower longitudinal rail is located 3 ft (0.9 m) below it.

On the traffic face of the barrier, 1 in. x 1 in. (25 mm x 25 mm) 11-gauge wire mesh is installed

with wire ties at three locations to each post.

The chain link fence has a distinct advantage that the impacts are distributed (non-

localized) along a wide contact patch. The small mesh size will ensure that impacting occupants

do not penetrate through the rail, and the round support posts reduce severity of impact by

distributing contact over a large area. There was concern that the mesh was not dense enough,

and motorcyclists or occupants which impact the barrier may project appendages (i.e. fingers)

through the mesh and suffer cuts or loss of fingers. However, analysis of approach vectors of

occupants and flailing motorcyclists indicate that there is a generally-low risk of such injuries

due to the extenuating circumstances required to activate such a response.

5COST ESTIMATE COMPARISONPreliminary cost estimates were assembled for the options discussed using the 2009

edition of the Building Construction Cost Data Manual published by RSMeans [14]. This

contains the national average for standard construction costs and location factors to compensate

for the differing construction prices at locations across the country. The estimated costs were


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normalized as costs per linear foot (LF) and linear meter (LM) of installation. This unit cost is

multiplied by the total length of installation to calculate the total cost of the project. However, it

should be noted that guardrail installation is highly specialized, and it is recommended to get

estimates from contractors experienced with guardrail installation to verify these estimates.

The estimated unit cost of the relocation option is $14.91/LF (48.92/LM), which is based

the relocation of the barrier and new material costs for chain link fence, impact attenuators, and

anchors. The total installation cost over approximately 6 miles (9.7 km) is $473,000. This option

is the lowest-cost option for redesigning the rail element; however, it may not be applicable at all

locations. Relocating the rail away from the concrete barrier may introduce additional free space

between individual joints at turns which was not included in the original manufacturing design.

Roadway curvature may cause unintended difficulty and confusion for construction crews, and

may lead to a significantly higher unit cost.

The estimated unit cost of the proposed retrofit design is $63.38/LF ($207.94/LM).

Therefore, the total cost to install the retrofit design on the approximate 6 miles (9.7 km) of

guardrail is $2,008,000. A possible alternative to installing this design over the entire portion of

the Boston Tunnel would be to only install the plate shielding on the curved sections of the

roadway. A benefit-to-cost analysis would be required, based on layout and traffic volume, to

decide the most critical areas for increased protection. The unit cost can be applied to the

required length of guardrail installation to determine total cost of the project.

The installation cost of the chain link combination rail is significantly less than that of the

proposed retrofit design, but is more than the anticipated cost of the rail relocation. An estimate

for demolition and removal cost was 25% more than the total construction cost. The demolition,

material, and installation cost of the chain link combination rail is $27.55/LF ($90.39/LM).


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However, this alternative requires the complete removal of the existing rail. The total installation

cost over the 6 miles (9.7 km) of guardrail is estimated at $873,000. This option is substantially

less expensive than the retrofit option. The costs associated with the three proposed options are

summarized in Table 1.

Table 1. Estimated Costs of Proposed Options

RelocationOptionItem Labor Material Equipment Total

Totalwith

Overhead

andProfit

($/LF) ($/LF) ($/LF) ($/LF) ($/LF)

ChainLinkFencing 0.41 1.20 0.11 1.72 2.01

Energy

Absorbing

Impact

Attenuators 0.37 1.37 0.00 1.73 2.01Anchors/Ties 3.55 1.01 0.36 4.92 6.69

RelocationofExistingBarrier 1.78 0.00 0.00 1.78 2.22

Totals 6.10 3.57 0.46 10.14 12.92

TotalIncludingLocationFactor: 14.91$

RetrofitOptionItem Labor Material Equipment Total

Totalwith

Overhead

andProfit

($/LF) ($/LF) ($/LF) ($/LF) ($/LF)3 ColdFormedCSections(16Ga.,8"Deep) 18.00 10.68 0.00 28.68 36.36

L4x31/2x1/4"AngleConnections 1.05 3.10 0.10 4.25 5.40

AttachmentstoExistingRail 7.15 0.38 0.00 7.53 13.16

Totals 26.20 14.16 0.10 40.46 54.92


ReplacementOptionItem Labor Material Equipment Total

Totalwith

Overhead

andProfit

($/LF) ($/LF) ($/LF) ($/LF) ($/LF)

ChainLinkFencingwithPosts 3.77 4.00 1.01 8.78 11.60

Anchors/BasePlate 3.50 2.00 0.10 5.60 7.50

Demolition/HaulOff 4.78

Totals 7.27 6.00 1.11 14.38 23.88


25%ofConstructionCost


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6DISCUSSIONIt should be clear that relocating the rail is the most cost-effective treatment method.

Relocation of the hazardous rail element reduces the chances of occupant or motorcyclist impact

with the rail altogether. Clearly, the risk of injury is minimal if the rail is located a long distance

from the side of the road. Although the liberty to use such space is significantly limited by the

width of the walkway, narrowing the walkway to the minimum permissible width is the best

option to reduce occupant and motorcyclist risk alike. If rail relocation is a possible venue of

approach, or if the walkway permits narrower paths, the only remaining problem is to make the

rail safe for motorcyclists, and all user groups will experience maximum safety benefit.

Occupants which make contact with the semi-rigid rail element proposed for the retrofit

will experience risk which is not present in the barrier replacement option and is minimized in

the relocation option. Head ejection during concrete barrier impacts results in up to an 11-in.

(279-mm) wide window in which the head may extend out of the vehicle. Occupants of

passenger vehicles which contact the retrofitted rail may experience greater lateral accelerations

due to impact with a semi-rigid structure than would be experienced if the rail were relocated.

Head impact into the rigid structure has been observed in accident reports and field investigation

to result in unconsciousness, loss of memory, hemorrhaging, concussions, and in rare occasions,

death. However, most data collected for the head ejection criteria was obtained from high-speed

testing at 60 mph, and clearly a smaller window of head ejection will occur at the posted speed

limit in the Boston Tunnel. Thus, although the retrofit option is the most costly and poses a

rigid-object hazard to occupants and motorcyclists because of its inherent stiffness, it is

significantly better than the current rail design by preventing impact with the plate posts, may


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offer an aesthetic improvement, is believed to be crashworthy, and will improve behavior of the

railing itself by minimizing snag potential. Therefore, this is a desirable option.

Clearly, the most desirable option is the replacement of the barrier with a chain link

fence. Although this option requires that the existing rail be removed, the reward due to safety

improvement and decreased liability is substantially higher than the temporary costs associated

with the idea. The chain link fence is highly versatile and adaptable, easily repaired in the event

of a significant impact, and has aesthetic appeal. Furthermore, the chain link fence design may

enable unparalleled roadside access for emergency personnel through the use of reinforced gates,

minimizing obstruction which may be present using the existing rail design. It should be noted

that gate designs are typically weak, and any design incorporating a gate will have to ensure

adequate continuity of strength if it can be impacted. By incorporating the benefits of the retrofit

through a more flexible and forgiving rail element, and the benefits of relocation through

portability and freedom to install wherever it is convenient, the chain link fence is the most

desirable option and is highly recommended.

A summary of rail modification considerations is shown in Table 2.


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Table 2. Summary of Characteristics of Redesign Options

Relocate Retrofit Replace

Accessibility Unchanged

Reduced. Continuous rail along the surface of

the barrier will require workers to either climb

the barrier or find a location with a break in the

rail segments.

Improved. Gates may easily be incorporated into

the chain link design.

Construction Time

Moderate to high. Shearing the epoxied anchors

into the concrete barrier for each barrier section,

then drilling new holes and fitting new rods will

require extensive construction time of the three

options. Plus, addition of retrofits and accounting

for curvature of roadway may introduce delays

and additional construction problems.

Minimal. No demolition is required, and rail

incorporation is s traightforward.

Moderate. Although this option also requires thatthe existing rail be removed from its existing

location, rail spacing of the new barrier is longer,

which requires less field-drilled holes for new

anchors. New ra il construction is also more

rapid.

Occupant Risk

Minimal. It is unlikely that occupants will impact

the barrier if it is located at least 11 in. from the

front face of the concrete barrier.

Moderate. Though risk of injury due to impact

with the posts is diminished, a new rigid hazard is

introduced which could pose a moderate risk.

Minimal. If the barrier may be placed out of the

zone of intrusion, there is little risk of impact. If

the barrier is located within the head-ejection

window, injuries are expected to be very minor.

Plus, since the rail is forgiving and the posts are

weaker than in the current rail, contact will be

less rigid and occupants will be better able to

withstand the non-local impact forces.

Motorcyclist Ris k

Moderate to high. Risk due to impact with theposts is decreased, but there is still risk of blunt

force trauma due to pocketing, plus minor injuries

including cuts, abrasions, and bruises due to

partial contact with chain link-post structures.

Moderate. The risk of injury becomes nearly

identical to the risk of injury for impact with a

concrete barrier.

Minimal to moderate. The system is the most

flexible and thus most forgiving during an impactsituation. It may be possible to cut or sever

fingers if motorcyclists impact with hands leading

toward the rail. However, weak posts enable

non-localized (distributed) contact and increased

system energy absorption.

Walkway Pede strian

Risk

Minimal. Chain link fence will retain

motorcyclists on the traffic side of the barrier,

and vehicle contact will be reduced.

Minimal. Virtually no rail deflection and

decreased snag lead to the lowest expected risk.

Moderate. Any person on the walkway

immediately behind a section of rail that is

impacted may experience risk of rail collapse and

unintentional inclusion in the impact.

Snag Potential

High. Although vehicles may have reduced

contact with the rail, any contact may lead to

snagging, particularly at end segments of each

rail. This can be alleviated by welding a 4"x2"

tube between the tops of every rail section.

Moderate. More of the deflection load will be

carried by the channel sections, increasing

barrier stiffness and reducing snag potential.

However, tall vehicles impacting at high speeds

and angles may snag at the upper corners of the

existing barrier.

Minimal. The chain link will not engage the

vehicle with sufficient force to cause the fence

to be pulled with the vehicle, and the posts are

not likely to cause snagging. However, gate

designs must reflect continuity to prevent

snagging at gates.

Maintenance

Requirement

Minimal to moderate. Impact frequency will be

reduced to very low percentages. Larger

vehicles may make contact with the rail and

cause damage, but this will likely be infrequent.

Motorcyclist impacts are not expected to cause

any permanent rail damage, but the chain link

fence may require maintenance.

Minimal to moderate . Vehicle interaction withthe stiff channels may cause localized yielding

and some damage to the channels, requiring post

replacement.

Moderate. If the system is located far from the

road, impacts may cause minor permanentdamage but the damage may be reversible

without replacement. If the system is located

near the roadside, vehicle impacts may require

occasional chain link fence repairs.

Crashworthiness

Low. Relocation is necessary to reduce risk of

impact with the rail, since it has demonstrated

low crashworthiness.

Medium. Decreased occupant risk and snagging

potential improve crashworthiness, but there is

still possibility to snag at the top of the barrier.

High. This design was already tested and

approved to AASHTO PL-2 status by the Texas

Transportation Institute.

CostMinimal. Low material costs offset re latively

high labor requirements.

High. Material costs are s ignificant, though labor

costs may be lower than other two options.

Low to moderate. Labor costs will constitute the

largest portion of the total cost. Efficient

construction will minimize cost of this design

option.

AestheticsLow. Design appears cluttered and lacks

consistency in design.

Moderate. The continuous rail element will add

continuity to the design and create a smoother

ambience.

Moderate. Chain link is aesthetic, but crashes

causing damage to the rail may diminish its

aesthetic appeal.

Public Perception

Marginal improvement. Aesthetically, the design

is lacking. Plus it incorporates the existing rail

which will diminish its apparent effectiveness.

Maximum improvement. Despite an intrinsic

occupant risk with the design, it will appear saferto motorists and is the most visible design

change.

Moderate improvement. Some motorists may

indicate that walkway protection is reduced;however, concrete barriers are responsible for

vehicle redirection, not the pedestr ian rail.

Maintenance Personnel

Reaction

Displeased. Walkway space will be reduced,

visibility is reduced, and public perception may be

poor.

Pleased. Walkway space is retained, though

visibility is reduced. Public perceptions of sa fety

are improved.

No change. Improvements in acce ssibility may

be countered by decreases in walkway space

and lower perception of rail strength and design.

RECOMMENDATIONUse if space available for relocation is

significant.

Use if there is no space for relocation and

walkway is very frequently used.

Use if funds and construction time are available

as the primary recommendation.


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7SUMMARY AND CONCLUSIONSDesign of the current Boston Tunnel guardrail was evaluated using finite element

analysis and compared to real-world accident history. The guardrail was relatively weak in

bending and would not prevent a vehicle which had climbed the traffic barrier from impacting

the guardrail and would allow the vehicle to penetrate the gaps between the rail and snag on the

posts, causing damage to the rail and deforming or potentially penetrating the occupant

compartment of the vehicle. If a motor-vehicle occupant or motorcyclist's head makes initial

contact with the posts, defenestration, severe spinal compression, or significant brain injury may

result. Likewise, occupants of errant vehicles, when subjected to the lateral accelerations in rigid

concrete barrier impacts, tend to project toward the impact-side window of the vehicle and may

extend out of the vehicle through the window. The head ejection analysis indicated a high

propensity for occupants of impacting vehicles to become snagged by the rail and, in worst-case

conditions, become wedged and removed from the vehicle.

Three modifications were proposed to increase the safety of the Boston Tunnel's

pedestrian guardrail design. The first option discussed was to relocate the barrier 7 in. (191

mm) backward from its current position. The second option was to install three 8-in. (203-mm)

wide folded plate retrofits on the front of the traffic barrier by installing attachment brackets on

the plate posts and drilling holes in the folded plates to install button-head bolts. This design

option prevents occupants from penetrating into the system and impacting the rail. A more cost-

effective, crashworthy option with less optical obstruction consisted of a bolted-down chain link

guardrail system installed on the top of the concrete barrier. This design has the advantage of

improved pedestrian and motorist vision, maintains aesthetics of the walkway, improves

motorcyclist safety, and prevents post snagging with the continuous rail element.


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The installation cost of the chain link combination rail is approximately 57 percent less

expensive than the proposed retrofit design. However, the cost of either solution is not

anticipated to be a significant cost to the Massachusetts Department of Transportation, based on

annual budgetary losses due to liability. Over the course of the last eight years, the State of

Massachusetts has already experienced equivalent or higher costs from liability lawsuits based

on the existing rail design. A relatively small investment in the safety of the Boston Tunnel could

save additional lawsuit costs as well as provide a safer roadway.

It is recommended that the Massachusetts Turnpike Authority consider a relocation,

retrofit or replacement of the Boston Tunnel guardrail immediately. The cost of litigation using

the currently non-crashworthy design is considerable, and the tunnel has a high fatality rate.

Following federally-accepted societal costs associated with motor-vehicle fatalities and critical

injuries [15], the annualized cost to the state from occupant injuries is more than $3.3 million per

year. As long as the existing rail is in place in its current location, the Massachusetts Department

of Transportation stands to incur a significant cost via litigation, plus reinforcing a societal

perspective of insensitivity on behalf of governing authorities. The expected payback period for

installation of either the retrofit design or recommended replacement design is less than one year,

if severe injuries and fatalities can be prevented. A new rail design may improve perceptions of

safety among motorists, societal perspective of transportation safety, and sensitivity to needs and

demands of the citizens.

8ACKNOWLEDGEMENTSThe authors would like to acknowledge Mr. Maurer, who provided funding for research

in this project. The authors would also like to express gratitude to Larry Bock and Drs. Dean

Sicking, Ronald Faller, and John Reid for their guidance and contributions to this project. This


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analysis was dedicated to the motorists who were killed during impact with the Boston Tunnel

railing. The authors also express appreciation to NCAC for use of the vehicle model.

9REFEERENCES1.Carroll, M., Review of tunnel handrails is urged, The Boston Globe, February 22, 2010.http://www.boston.com/new/local/massachusetts/articles/2010/02/22/review_of_tunnel_handrail

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2.Gabler, H.C., "The Risk of Fatality in Motorcycle Crashes with Roadside Barriers", Paper No.07-0474, 2007, .

3.Guide Specifications for Bridge Railings, American Association of State Highway andTransportation Officials (AASHTO), Washington, D.C., 1989.

4.Ross, H.E., Sicking, D.L., Zimmer, R.A., and Michie, J.D., Recommended Procedures for theSafety Performance Evaluation of Highway Features, National Cooperative Highway ResearchProgram (NCHRP) Report No. 350, Transportation Research Board, Washington, D.C., 1993.

5. Manual for Assessing Safety Hardware, American Association of State HighwayTransportation Officials, Washington, D.C., 2009.

6.Polivka, K.A., Faller, R.K., Keller, E.A., Sicking, D.L., Rohde, J.R., and Holloway, J.C., Design and Evaluation of the TL-4 Minnesota Combination Traffic/Bicycle Bridge Rail, Final

Report to the Midwest States Regional Pooled Fund Program, Transportation Research Record

No. TRP-03-74-98, Midwest Roadside Safety Facility, University of Nebraska-Lincoln,

November 1998.

7.Buth, C.E. and Megnes, W.L., Crash Testing and Evaluation of Retrofit Bridge Railings andTransition, Report No. FHWA-RD-96-032, Submitted to the Office of Safety and Traffic

Operations R&D, Federal Highway Administration, Performed by Texas Transportation

Institute, Texas A&M University, College Station, Texas, January 1997.

8.LS-DYNA Keyword Manual version 971 R5.0, Livermore Software Technology Corporation,Livermore, California, 2010.

9.Rosenbaugh, S.K., Sicking, D.L., and Faller, R.K., Development of a TL-5 Vertical Faced

Concrete Median Barrier Incorporating Head Ejection Criteria, Final Report to the Midwest

States Regional Pooled Fund Program, Midwest Research Record No. TRP-03-194-07, Midwest

Roadside Safety Facility, University of Nebraska-Lincoln, December 2007.


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10.Wiebelhaus, M.J., Polivka, K.A., Faller, R.K., Rohde, J.R., Sicking, D.L., Holloway, J.C.,Reid, J.D., and Bielenberg, R.W., Evaluation of Rigid Hazards Placed in the Zone of Intrusion,

Final Report to the Midwest States Regional Pooled Fund Program, Midwest Research Report

No. TRP-03-151-08, Midwest Roadside Safety Facility, University of Nebraska-Lincoln,

January, 2008.

11.Final Report of the Motorcyclists and Crash Barriers Project, Federation of EuropeanMotorcyclists' Association, 2005, .

12.The Road to Success, Federation of European Motorcyclists' Association, July 2005,.

13.AISI Cold-Formed Steel Design Manual, American Iron and Steel Institute, 2009.14.Building Construction Cost Data, 67th Edition, R.S. Means Company Inc., 2009.15. Roadside Design Guide, American Association of State Highway Transportation Officials,Washington, D.C., 2007.

Documents

Boston Tunnel Report, Oct. 1, 2010