Celebrating 125 Years

Transportation FAQ

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  • Q1: What can I do as a rider of mass transit to help reduce the risk of COVID-19 spread?

    A: The easiest way to avoid becoming infected while traveling is to not travel in the first place. If travel is not essential, it is advisable to reconsider your travel plans. However, many workers in essential services still require the use of public transportation systems, and riders of mass transit should factor this into their plans. Please see Technical Guidance for Transportation – Guidance for Mass Transit Riders for more information.

  • Q2: What guidance is available for air passengers to help reduce the risk of COVID-19 spread?

    A: Air passengers can help reduce the spread of COVID-19 by wearing facemasks, practicing social distancing, and travelling only if the travel is necessary. Please see Technical Guidance for Transportation – Guidance for Air Passengers, for detailed suggestions.

  • Q3: Is there guidance available for Transportation Facility Operation? Is guidance for similar commercial buildings appropriate?

    A: Many transportation facilities are very much like other buildings that superficially share usage types. But there are very important differences between transportation facilities and other similar commercial buildings (office buildings, malls, etc.):

    1. Occupants of the facility are often on their way to or have come from other locations (other neighborhoods, cities, states, and countries).
    2. The facility may be subject to a great deal more regulation.
    3. The facility may have tenants (operators of the transport services using the facility) that are subject to even more regulation by a different set of agencies or bodies.

    ASHRAE recommends following the guidance in the Task Force’s Technical Guidance for Transportation – Guidance for Transportation Facility Operation.

  • Q4: What is the best/safest place to sit on an airplane?

    A: Experimental data show there are no particularly good or bad seat locations in typical airliners with respect to risk for airborne disease transmission. The primary factor in this risk is how well ventilation air is supplied to a given location as it is this ventilation air that flushes airborne pathogens out of the cabin. The more quickly and effectively this supply air flushes airborne pathogens from the air, the lower the risk, all other factors being equal. 

    Airliners are designed to supply ventilation air uniformly along the length of the cabin. However, that feature alone does not ensure that every seat gets the same ventilation. Experiments were conducted in full-sized mockups of both wide-body and narrow body aircraft using actual aircraft air delivery systems and design flow rates.1,2 Effective local ventilation rates were measured at each seat, 30 seats in the narrow-body and 77 seats in the wide-body. Effective local ventilation is a measure of the amount of air supplied to the cabin adjusted by the effectiveness with which it reaches a given location.  For the narrow body aircraft, the effective local ventilation rates varied from 29 to 32 air changes per hour (Note: Since HEPA filtration of recirculated air is standard practice in nearly all airliners, effective ventilation rate is based on total airflow, not outside airflow, for airborne pathogen applications.).  For the wide body, it varied from 24 to 28 air changes per hour.  These differences within an aircraft are not of practical importance and there was no discernable pattern as to which seats had the higher values (e.g. window versus aisle).

    Another study showed that the biggest factor in exposure risk, not surprisingly, is distance from the infected person.3 The further you are from the infected person in any direction, the better.  While it is not possible to know in advance the location of infected people, the fewer people in the general vicinity of a seat and especially the fewer people within 2-3 seats in any direction, front-back, right-left, the lower the risk.  This same study indicated the worst place to be for airborne transmission may be directly in front of an infected person. 

    Since seats are spaced further apart in both directions in business and first-class sections, the risk in these sections is likely somewhat less in a fully loaded aircraft.  However, a fully loaded first class section may have a higher occupant density than a lightly loaded main cabin, thus, there is no guarantee that a 1st class seat will reduce exposure.


    1) J. Patel, B. Jones, and M. Hosni, Experimental Analysis of Ventilation Effectiveness and Tracer Gas Dispersion in a Boeing-737 Mockup Cabin, Proceedings of the Second International Conference on Energy and Indoor Environment for Hot Climates, ASHRAE, February 2017, Doha, Qatar.

    2) J. Patel, B. Jones, M. Hosni, A. Keshavarz, Experimental Investigation of Ventilation Effectiveness in an Airliner Cabin Mockup, Proceedings of the ASME 2016 International Mechanical Engineering Congress and Exposition, IMECE2016,  Phoenix AZ, November 12, 2016

    3) J.S. Bennett PhD , B.W. Jones, M.H. Hosni, Y. Zhang, J.L. Topmiller, and W.L. Dietrich, Airborne Exposure Patterns from a Passenger Source in Aircraft Cabins,  HVAC&R Research, 22 Nov 2013.

  • Glossary

    CIDRAP = U of MN Center for Infectious Disease Research and Policy

    DMHC = ASHRAE Design Manual for Hospitals and Clinics (First Edition)

    WHO = World Health Organization


    ASHRAE PD = ASHRAE Position Document on Infectious Aerosols

    FGI = Facility Guidelines Institute


    Term Definition Source
    Aerosol generating procedure (AGP) Procedures that are likely to induce coughing. Procedures that are believed to generate aerosols and droplets as a source of respiratory pathogens include positive pressure ventilation (bi-level positive airway pressure [BiPAP] and continuous positive airway pressure [CPAP]), endotracheal intubation, airway suction, high-frequency oscillatory ventilation, tracheostomy, chest physiotherapy, nebulizer treatment, sputum induction, and bronchoscopy. AGPs should ideally take place in an airborne infection isolation room (AIIR). CDC
    Aerosol, infectious An infectious aerosol is a system of liquid or solid particles uniformly distributed in a finely divided state through a gas, usually air. (They are small and buoyant enough to behave much like a gas yet they can be filtered out of the gas.) ASHRAE PD
    Aerosol, Short-range transmission Transmitting disease by inhalation of aerosols near the source. The distance for this transmission has not been studied beyond two meters. CIDRAP
    Age of Air The time that has elapsed after the air enters a space (at any given point.) DMHC
    Air change rate Airflow in volume units per hour divided by the building space volume in identical volume units (normally expressed in air changes per hour [ACH or ACPH]) DMHC
    Air irritant A particle or volatile chemical in air that causes physiological response when in contact with mucosa in the eye, nose, or throat. DMHC
    Air volume migration The volume of air that is exchanged during room entry/exit (through a door-way between a room and the area beyond its door) DMHC
    Air, exhaust Air removed from a space and discharged outside the building by mechanical or natural ventilation systems. DMHC
    Air, makeup Any combination of outdoor and transfer air intended to replace exhaust air and exfiltration. DMHC
    Air, outdoor (1) Air outside a building or taken from the outdoors and not previously circulated through the system;
    (2) Ambient air that enters a building through a ventilation system, through intentional openings for natural ventilation, or by infiltration.
    Air, recirculated Air removed from a space and reused as supply air. DMHC
    Air, supply Air delivered by mechanical or natural ventilation to a space that is composed of any combination of outdoor air, recirculated air, or transfer air. DMHC
    Air, transfer Air moved from one indoor space to another. DMHC
    Airborne droplet nuclei Small-particle residue (5 µm or smaller) of evaporated droplets containing microorganisms that remain suspended in air and can be dispersed widely by air currents with a room or over a long distance. DMHC
    Airborne infection isolation room (AIIR) A room designed with negative pressurization to protect patients and people outside the room from the spread of microorganisms (transmitted airborne droplet nuclei) that infect the patient inside the room. DMHC
    Airborne infectious agent An airborne particle that can cause an infection. DMHC
    Airborne pathogen An airborne particle that can cause disease. DMHC
    Airborne transmission Airborne transmission is defined as "dissemination of either airborne droplet nuclei or small particles in the respirable size range containing infectious agents that remain infective over time and distance." An important requirement of airborne transmission is that it can occur only at a long distance from the source, according to the CDC. CIDRAP
    Air-cleaning system A device or combination of devices used to reduce the concentration of airborne contaminants, such as microorganisms, dust, fumes, respirable particles, other particulate matter, gases and/or vapors in air. Related term: HEPA Filter. DMHC
    Anteroom A room separating an isolation room from a corridor. DMHC
    Bay (patient) A space for human occupancy with one hard wall at the headwall and three soft walls. FGI
    Bioaerosol Particles or droplets suspended in air that consist of or contain biological matter such as bacteria, pollens, fungi, skin flakes, and viruses. DMHC
    Building air infiltration Uncontrolled inward leakage of air (that may contain entrained water vapor) through cracks and interstices in any building element and around windows and doors of a building, caused by the pressure effects of wind or the effect of differences in the indoor and outdoor air density. DMHC
    CADR Clean Air Delivery Rate which is the combined effect of actually how much air is moved through the filter and the filter efficiency. AHAM AC-1
    Community acquired infection An infection present or incubating in a patient upon admission to a hospital (or who subsequently shelters in place outside the hospital). DMHC
    Contaminant or Pollutant Any impurity, any material of an extraneous nature, associated with a chemical, a pharmaceutical preparation, a phuysiologic principle, or an infectious agent. DMHC
    Contaminant, airborne An unwanted airborne constituent that may reduce the acceptability of air. DMHC
    Contamination The act of contaminating, especially the introduction of disease germs or infectious material into or on normally sterile objects. DMHC
    COVID-19 COVID-19 is the short name for “coronavirus disease 2019" WHO
    Cubicle A space intended for human occupancy that has at least one opening and no door and is enclosed on three sides with full height or partial height partitions. FGI
    Droplet transmission Droplet transmission is defined as "respiratory droplets carrying infectious pathogens that transmit infection when they travel directly from the respiratory tract of the infectious individual to susceptible mucosal surfaces of the recipient, generally over short distances, necessitating facial protection." Close contact involves hand transfer of surface contamination to mouth, nose or eyes, hand washing and gloves being common controls. CIDRAP
    Epidemiology Study of the distribution and determinants of disease. DMHC
    HEPA filter (or absolute filter)  High efficiency particle air filter with an efficiency of 99.97% removal of particulates larger than 0.30 microns. DMHC
    Hospital Acquired Infection (HAI) See Nosocomial infection.
    Intensive care rooms (ICU)(also critical care rooms CCU) Rooms in which the level of patient care and electronic monitoring of patients are greatly increased over conventional patient rooms. FGI
    MERV Minimum Efficiency Reporting Value: The fraction of particles removed from air passing through a filter is termed “filter efficiency” ASHRAE 52.2-2017
    Nosocomial infection (or Hospital Acquired Infection [HAI]) An infection that is acquired in a hospital and that was not present or incubating upon admission. DMHC
    Occupationally acquired infection An infection acquired while working in a medical care setting. DMHC
    Opportunistic organism An ordinarily non-infectious agent that becomes infectious in an immunocompromised host. (any novel organism, especially aerosolized respiratory viruses for which there is no vaccine or herd immunity becomes an opportunistic organism.) DMHC
    Pneumonia Inflammation of lung tissue. DMHC
    PPE Personal Preotective Equipment is equipment worn to minimize exposure to hazards that cause serious workplace injuries and illnesses. Occupational Safety and Health Administration, PPE
    Pressurization A difference in pressure between a space and a reference pressure. DMHC
    Room A space enclosed by hard walls and having a door. FGI
    SARS-CoV-2 Severe Acute Respiratory Syndrome CoronaVirus 2 International Committee on Taxonomy of Viruses (ICTV)
    UV Ultraviolet irradiation. DMHC
    UVGI Ultraviolet germicidal irradiation. DMHC
    Ventilation A process of supplying air to or removing air from a space for the purpose of controlling air contaminant levels, humidity, or temperature within the space. Such air may or may not have been conditioned. DMHC
    Ventilation effectiveness The ability of a system to remove contaminants generated by a source in a room. DMHC