Page 343 - Moving the Earth_ The Workbook of Excavation

ROADWAYS

ROADWAYS 8.5

The runway may have a level centerline, crowned up from the sides slightly for drainage, or
have a flat cross section and a longitudinal slope. In either case drainage slopes are very slight,
and the surface must be exactly on grade to avoid puddles.
Taxiways and plane parking areas are roads surfaced to an ample width to carry the wheels of
a plane running on the ground. Additional areas on each side must be cleared and lowered to allow
clearance for the wings.
Airport subgrades and pavement may have to exceed standards for heavy truck highways if
maximum size planes are to be carried.
Road Markers. A construction or mining road should be plainly marked as such, to prevent
accidental entrance by motorists. Cars and big machinery do not mix well, and also drivers who
are lost or confused may get in the way of a blast or run off a cliff.
Warning signs should be placed on highways at least 400 feet on each side of a haul road crossing.
If either road is a busy one, the intersection should be protected by a flagman or a traffic light.
One-way haul roads should be marked plainly and frequently with direction signs. There should
be a sign wherever any vehicle could enter, and additional signs along the roadways to warn drivers
going the wrong way. If the road is paved, arrows should be painted on the pavement, pointing in
the direction of travel. A conventional dashed stripe line down the center could have arrowheads
painted on some of the dashed lines.
Signs at entrances to one-way sections are not enough, as they may be destroyed by accident
or vandalism, or obscured.
Failure to provide sufficient notice and warning of traffic direction is the cause of many head-on
crashes on divided state and federal highways. There the blame is put on the wrong-way driver,
but in a private construction road the contractor is likely to be held responsible.

ROADWAY LAYOUT

Roadways are planned and staked out with consideration for horizontal alignment, vertical align-
ment, and cross section.

Horizontal Alignment. Horizontal alignment is the route as it would appear on a map, with
detail enough to enable field engineers and contractors to lay out and build the road exactly as it
was planned. It is figured in terms of the location of the centerline.

Curves. Curves are laid out as arcs of circles. Each point on such an arc is equally distant from
the center of the circle that would be formed by continuing the arc on the same curve. See Fig. 8.2.
A curve is described or defined by its degree of curve or by the length of its radius. Its degree
of curve is the number of degrees in the angle at the center that is made by drawing lines from the
center to points on the curve that are 100 feet apart. A sharp curve will have a higher degree of
curve than a gradual one.

FIGURE 8.2 Curve and tangents.