4_route location and survey

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KAAF UNIVERSITY COLLEGE

Civil Engineering DepartmentCollege of Engineering

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Highway Engineering 1CIV 368

Lecture 4_ Route Location and Survey

Kwasi Agyeman Boakye ( [email protected])

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Examination of natural and man-made features

Preparation of different overlays showing different features.

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Examination of natural and man-made features

Aerial Photographs Examine the stereoscopic aerial photographs to determine whether topographic and culturalfeatures are different from those shown in the map. Document any changes on an overlay so that this may be recorded on the map. Examine the oblique photographs to obtain a sense of the developmental and aesthetic

features of the area and a general idea of the grades and other topographic characteristics.These should be checked with those on the map to ensure correspondence.

It must be noted in particular that the presence of trees may make identification of the groundsurface features difficult on aerial photographs. Also local features that may be environmentallysensitive to the presence of a proposed road should be identified.

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Identification of TechnicallyFeasible Alternatives

The idea of identifying routes is to improve connectivity between origins and destinations. Thismeans making connectivity less expensive and safer for public in general as well as for the roaduser, while at the same time maintaining or contributing to the improvement of environmentalquality.

A route is described as technically feasible where no excessive construction or maintenanceproblems are envisaged, and design controls and policy on geometric design standards areadhered to.

A route may be technically feasible but not economically justifiable or environmentallyacceptable. The only way to determine economic viability or environmental acceptability is toconduct preliminary design and based upon expected costs, benefits, and likely environmentalimpacts, conduct an environmental and economic evaluation.

This may result in a Preliminary Project Report to proceed for Detailed Project Report, after modification or re-evaluation, or be dropped from further consideration.

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Guidelines for SelectingTechnically Feasible Routes

1. Run the alignment on as high a ground (ridge lines) as possible.2. Run the alignment on soils that provide better subgrade support, consequently reducing

pavement cost .3. Run the alignment that satisfies the required design standard4. Avoid the alignment passing through village streets when the road connects a chain of

villages; preferably, the alignment should skirt around village5. Study the problem of land acquisition, avoiding it to the extent possible6. Consider proximity of road construction material7. Avoid marshy and water logged areas, areas of poor subgrade support, expansive soil

areas, etc to the extent possible.8. Run the alignment to keep minimum construction, maintenance and travel operation cost.

9. Avoid the alignment with sharp curves, areas of poor visibility etc so that the required sightdistance are available.

10. Run the alignment with due consideration to safety aspects for various junctions especiallythe ones connecting main highways.

11. Run the alignment to cross major rivers in perpendicular direction.

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Selection of Preferred Alignment

The typical approach for selecting a preferred alignment includes compromising between theuser costs and construction costs while seeking the route and physical conditions that result

least adverse environmental impact.

How is a balance struck between the user costs and construction costs?

The basic task is to predict the Total Life Cycle Cost (construction, maintenance and road user costs) as a function of the road design, maintenance standards and other policy options whichmay be considered.

The preferred alignment can only be determined by comparing the total costs for users and theconstruction as well as maintenance costs incurred by the implementing agency for eachtechnically feasible alternative and selecting the alternative with the least monetary cost and

acceptable non-quantifiable impacts.

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Developing and CheckingAlternative Alignments

- A preliminary analysis is done on a route from A to B.-A reasonable short route is taken (Route 1)and examined.Analysis Route 1-Draw the horizontal alignment to scale-Convert route into a series of tangents andand check the minimum allowable radius-Check the intersection angles-Construct the existing grade profile-Establish vertical alignment without exceedingpermissible gradient and maximum height of cut andfill.

Summary Route 1Inability of Route 1 to provide acceptable gradientsatisfying the cut and fill requirements. Somewhatsimilar route is unacceptable-explore alternatives.

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A B

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135 145

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135 100

Route 1

E l e v a t i o n

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Developing and CheckingAlternative Alignments

Two other alternatives are tried.Route 2 and Route 3

Analysis of Route 2 and 3-Follow same initial procedure as route 1

Summary of Route 2Route 2 is technically feasible. Cuts and fills appear toto be balanced. However each engineer may arriveat a slightly different geometric design at least for preliminary effort.

Summary of Route 3Route 3 is also a technically feasible route.

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A B

90 100 135 145 160

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135 100

Route 2

Route 3

E l e v a t i o n

Length

E l e v a t i o n

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Screening and selection of routefor preliminary design

Both Routes 2 and 3 are technically feasible (Allowable grade, cut and fill depths, horizontal andvertical alignments). Route 1 is clearly inadequate.

In conclusion: Reject route 1. Route 2 and Route 3 should be investigated further by means of an initial economic analysis before a detailed design is taken.

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CriteriaScreening Evaluation

Route 1 Route 2 Route 3LengthDesign ControlsCut and Fill BalanceNeed for Special StructuresEnvironmental ImpactPotential High Cost Items


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Non-Standard Provisions

Situations may occur where terrain cannot be strictly followed requiring more fills or more cuts or other remedial solutions.

For mountainous areas it can be difficult to safety design control criteria without bridges, tunnelsor severe cuts etc. A possible solution is to use sharp curves or speed restrictions or bridges or

tunnels. In such situations detailed analysis must be done with cost implications. The finaldecision often based on the Total Life Cycle Cost Analysis.

Drainage Considerations An initial drainage design indicating the main locations of the catchments, ditches, culverts andbridges are important.

Alignment may be altered if the road cannot be adequately drained or if it adversely affectsexisting drainage pattern.

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Route location in Urban and RuralAreas

Route location has some differences in urban and rural areas. As such challenges should betreated separately.

Rural Areas-For any chosen route through a rural area there should be a consideration of existingpopulation and likely population of the area. Also origin and destination patterns should be well

considered.- Alternative routes in the immediate vicinity should be considered. It is existing condition,capacity, existing traffic volume, chances of future improvement etc should be looked at.- Not too steep gradients should be used. Where it might pose a problem for HGVsclimbing/crawler lanes should be provided for them.- Avoid a lot of earthworks by balancing cuts and fills. Also as much as possible reduce haulagedistance and movement of heavy equipment.- Where route goes by bridge or viadact consideration must be given to river traffic clearanceand position and channel of river must be considered.- Roads over rails are always preferred. Roads can cross where rail is in cutting.- The natural topography should be much followed where natural view is pleasant. However monotony should be avoided.-Property taking must be reduced especially where there are valuable agricultural lands and

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Route location in Urban and RuralAreas

Urban Areas-In urban areas much should be done to maintain contiguous junctions whiles increasingcapacity.- Traffic pollution should be also considered. Traffic noise which is a major source of pollutioncan be reduced by using sound barriers.

- Constructed roads should be designed such that visual obstruction and intrusion is reduced.The scale of road should be relative to adjacent development.- Severance by splitting communities by road being in cut or on high embankment should beminimized.

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