ack-filled
and tamped around the pipe. The joints in the pipe should be filled
with cement mortar, or should be of a design that will be tight.

=Endwalls for Culverts.=--A substantial retaining wall is placed at
each end of the culvert barrel, whatever the type. This is to prevent
the end of the culvert from becoming choked with earth and to retain
the roadway at the culvert. It also indicates to the drivers the
location of the end of the culvert. The endwall extends a foot or more
below the floor of the culvert to prevent water from cutting under the
barrel. Plain concrete or stone masonry are most commonly used for
culvert endwalls.

[Illustration: Fig. 4.--Two Types of Drop Inlet Culvert]

=Reinforced Concrete Box Culverts.=--The pipe culvert is limited in
application to the smaller waterways. Reinforced concrete is
extensively used for culverts of all sizes, but especially for the
larger ones. These are usually constructed with endwalls integral with
the barrel of the culvert. Culverts of this type must be designed for
the loads anticipated to insure suitable strength and stability, and
must be constructed of a good quality of concrete. Figs. 2 and 3 show
designs for pipe and box culverts.

[Illustration: Fig. 5.--Drop Inlet Culvert]

=Drop Inlet Culverts.=--In some locations erosion has begun in the
fields adjacent to a culvert and it will probably continue until the
stream above the culvert has eroded to about the level of the floor of
the culvert. This is a reason for placing the culvert as high as the
roadway will permit, so long as the area above the culvert will be
properly drained. Considerable reclamation of land is possible if the
culvert is constructed with a box at the inlet and as shown in Fig. 4.
The area up-stream from the culvert will not erode below the level of
the top of the box at the inlet end.

Where the stream crossing the road has eroded to considerable depth or
has considerable fall, as would sometimes be the case on side hill
roads, the culvert barrel would follow the general slope of the ditch
but should have a drop inlet. This type of culvert is shown in Fig.
5.

CHAPTER IV

ROAD DESIGN

=Necessity for Planning.=--Sometimes highway improvement is the result
of spasmodic and carelessly directed work carried out at odd times on
various sections of a road, finally resulting in the worst places
being at least temporarily bettered. The grade on the steepest hills
is probab