Mechanical ventilation for train operation in tunnels is an individual problem which must be analyzed
for each location. Generally, it will not be required in tunnels less than 2,500 feet long. In longer tunnels,
requirements will depend upon such conditions as type of locomotives, grades, length of train, speed,
time between trains, ambient temperatures, prevailing winds and drafts.
b. In marginal cases, overheating of locomotives may be reduced by radiator sprays and/or placing a curtain
at the departure end of the tunnel which will increase pressure within the tunnel and the amount of air
moving through the radiator. In very long tunnels, fan installations will be required to prevent
overheating and to remove smoke and gases.