Geometric Design Manual-2002
Cross Section Elements
Ethiopian Roads Authority
A cross-section will normally consist of the carriageway, shoulders or curbs, drainage
features, and earthwork profiles. These terms are defined in the Definition portion of the
manual text; major elements are repeated here for clarity:
Carriageway- the part of the road constructed for use by moving traffic, including
traffic lanes, auxiliary lanes such as acceleration and deceleration lanes, climbing
lanes, and passing lanes, and bus bays and lay-byes.
Roadway- consists of the carriageway and the shoulders, parking lanes and viewing
Earthwork profiles- includes side slopes and back slopes
For urban cross-sections, cross-section elements may also include facilities for pedestrians,
cyclists, or other specialist user groups. These include curbs, footpaths, and islands. It may
also provide for parking lanes. For dual carriageways, the cross-section will also include
medians. Typical Cross Sections are illustrated in Appendix E of this manual. Bus lay-byes,
parking lanes, passing lanes, and viewing areas are presented in Chapter 14.
Lane and shoulder widths should be adjusted to traffic requirements and characteristics of
the terrain. The cross-section may vary over a particular route because these controlling
factors vary. The basic requirements are, however, that changes in cross-section standards
shall be uniform within each sub-section of the route and that any changes of the cross-
section shall be effected gradually and logically over a transition length. Abrupt or isolated
changes in cross-section standards lead to increased hazards and reduced traffic capacity and
complicate construction operations.
In certain cases, however, it may be necessary to accept isolated reductions in cross-section
standards, for example when an existing narrow structure has to be retained because it is not
economically feasible to replace it. In such cases a proper application of traffic signs and
road markings is required to warn motorists of the discontinuity in the road. However, all
such narrow structures must be widened or replaced however when the width across the
structure is less than the adjacent carriageway width.
A feature of a highway having great influence on safety and comfort is the width of the
carriageway. Lane widths of 3.65m are used for Design Classes DS1 and DS2. The extra
cost of 3.65 m above that for 3.0 m is offset to some extent by a reduction in cost of shoulder
maintenance and a reduction in surface maintenance due to lessened wheel concentrations at
the pavement edges. The wider 3.65m lane also provides desired clearances between large
commercial vehicles on two-way rural highways.
Narrower lanes are appropriate on lower volume roads. Standards for carriageway widths