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The scan team asked the tunnel owners how they define a tunnel in their agency and whether any consideration is given to length, type of construction, ventilation, or lighting in developing their definition. The team also gave the owners the opportunity to propose changes to the AASHTO tunnel definition.

2.1.3.1 Current Definitions Used by Owners

The definition of a tunnel varies among owners. The simplest definition is “a structure mined or bored through undisturbed material.” Several use the NFPA 502 definition, “An enclosed roadway for motor vehicle traffic with vehicle access that is limited to portals.” Others define their tunnels by ventilation and lighting. Some do not have a specific definition.

Caltrans: To date, Caltrans Structure Maintenance & Investigations (SM&I) has not had a need

to define a tunnel other than for classifying its design-type in the National Bridge Inventory (NBI). SM&I defines a tunnel as a structure mined or bored through undisturbed material. Other Caltrans functional units may have their own tunnel definitions. Refer to the definition in the Caltrans response in Section 2.1.3.2. The definition is based on the tunnel’s capability of developing a toxic environment.

Colorado DOT: Tunnels are enclosed roadways with vehicle access that is restricted to portals. District DOT: DDOT believes length, type of construction, ventilation, and lighting are all

factored into defining a tunnel.

MassDOT: MassDOT believes that the definition is not as important, as tunnel inspection is

similar to that for bridges. However, the definition matters if specific life-safety systems are associated with the structure. The largest determinant is ventilation. Length is less reliable, as the structure’s cross section and the type of vehicles allowed to travel within the structure also affect when ventilation is required. Setting a rigid length guideline can be problematic if conditions of fire risk are not taken into account. Lighting and pump stations are not very informative, as they are often required in underpass situations. MassDOT does not consider roadway bridges over roadways to be tunnels.

PennDOT: PennDOT defines its tunnels by lighting and ventilation and follows the AASHTO

definition in its tunnels to a certain degree; however, it has no specific tunnel definition in its policies. Three of the four state owned tunnels in the Pittsburgh area have ventilation and electrical systems, including lighting, and were constructed using the traditional excavate/brace as you go method. The fourth tunnel has lighting and no ventilation, but was constructed in a manner similar to that used for the other three tunnels.

PANY&NJ: The PANY&NJ uses the definitions as provided by NFPA 502 and complies with its ventilation requirements.

VA CBBT: The CBBT District is not an agency and to date has not had the need to define tunnel. VDOT: VDOT uses the NFPA 502 and AASHTO T-20 definitions.

WSDOT: WSDOT currently makes no distinction for structure type. If the structure is reported as

a tunnel, WSDOT inspects it as a tunnel.

2.1.3.2 Proposed Changes to AASHTO Tunnel Definition

The tunnel owners were asked if the AASHTO tunnel definition works for them and, if not, what changes they would recommend. The AASHTO tunnel definition is copied below:

Tunnels are defined as enclosed roadways with vehicle access that is restricted to portals regardless of type of structure or method of construction. Tunnels do not include highway bridges, railroad bridges or other bridges over a roadway. Tunnels are structures that require special design considerations that may include lighting, ventilation, fire protection

systems, and emergency egress capacity based on the owner’s determination.

Some tunnel owners accept the current AASHTO definition without change. Others would like to include a minimum length and life-safety items, including ventilation, fire protection, emergency egress, and lighting.

Caltrans: SM&I does not necessarily agree with the last sentence of the definition. To date, SM&I

has not had a need to define a tunnel other than for classifying its design-type in the NBI. SM&I defines a tunnel as a structure mined or bored through undisturbed material. The needs of all Caltrans functional units will need to be considered.

The AASHTO definition does not distinguish shorter structures that do not fit within the NFPA 502 definition of a tunnel, but contain the particular conditions of traffic and orientation that result in air quality issues. Caltrans believes that all tunnel type structures have one common issue: the potential for hazardous exposure levels of carbon monoxide (CO) to traffic. Without that criterion, the structure is not a “tunnel.” Caltrans offers the following definition that distinguishes a tunnel capable of having a toxic environment from a long enclosed structure. Caltrans uses this as a working definition for classifying structures for inspection as tunnels:

Tunnels are enclosed roadways with vehicle access that is restricted to portals regardless of type of structure or method of construction. A structure’s classification as a tunnel is based on vehicle emission exposure. Roadway structures are tunnels when enclosed enough with access portals, with particular geographical orientation, and with particular traffic geometrics, for computational modeling to show the potential for hazardous vehicle emissions (principally CO, as defined by the EPA) to accumulate to hazardous exposure levels. Tunnels are not dependant on structure length and do not usually include highway bridges, railroad bridges, or other bridges over a roadway. Tunnels are structures that can require special design considerations that may include lighting, ventilation, fire protection systems, and emergency egress capacity, as documented in design standards or based on the owner’s determination.

MassDOT: MassDOT believes that some of the European definitions are useful and should be

reviewed. The reference to bridges seems unnecessary as owner determination is there. MassDOT recommends the following revision:

Roadways enclosed on sides and above or enclosed with minimal openings on sides and above with vehicle access that is restricted to a portal or another tunnel regardless of type of structure or method of construction. They are roadway structures that require consideration of systems and procedures to accommodate the enclosed nature of the roadway that may include ventilation, fire protection, emergency egress, and lighting based on the owner’s determination.

PennDOT: PennDOT concurs with AASHTO’s definition. The PTC has no objection, although

VA CBBT: The CBBT District believes a minimum length should probably be considered.

VDOT: VDOT believes that cargo restrictions based on the design fire size should be incorporated. WSDOT: WSDOT believes that a length component would add value to the definition. As it states,

a tunnel may include a series of safety related components that are to be defined by the owner. The majority of these features are in some way related to length.