The line in course of construction traverses an extremely hilly
region. The starting and terminal points are at the levels of 2,338
feet (Mendoza) and 2,706 feet (Santa Rosa) above the sea; the lowest
neck of the chain is at the level of 11,287 feet.

Study having shown that a direction line without tunnels, and even
with the steepest gradients for traction by adhesion, would lead to a
considerable lengthening of the line, and would expose it to
avalanches and to obstructions by snow, there was adopted upon a
certain length a rack track of the Abt system, with gradients of 8 per
cent., and the neck is traversed by a tunnel 3 miles in length and
1,968 feet beneath the surface. The number and length of the tunnels
upon the two declivities, moreover, are considerable. They are all
provided with rack tracks. The first 80 miles, starting from Mendoza,
are exploited by adhesion, with maximum gradients of 2½ per cent. Upon
the remaining 64 miles, traction can be effected either by adhesion or
racks.

[Illustration: FIG. 1.--REGION TRAVERSED BY THE RAILWAY THROUGH THE
ANDES.]

The track is of 3.28 foot gauge, and this will necessitate
trans-shipments upon the two systems. The rails weigh 19 pounds to the
running foot in the parts where the exploitation can be effected
either through adhesion or racks, and 17 pounds in those in which
adhesion alone will be employed.

[Illustration: FIG. 2.--DIRECTION LINE OF THE RAILWAY THROUGH THE
ANDES.]