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Chapter 3: Route alignment and road geometry

This chapter describes topographical survey and highway geometry practice during the period of motorway construction. It deals in three separate parts with:

  • topographical survey;
  • route alignment;
  • layout standards.

In each case the material is presented in the form of a narrative starting with the state of the art prior to motorway construction. It is a summarised version of a more complete and comprehensive document compiled by Bill Gallagher and entitled 'Road geometry', which is lodged in the Archive. Students and researchers may wish to consult the Archive document for its more comprehensive coverage. In compiling the Archive document and this chapter Bill received helpful contributions from many sources, in particular Gordon Craine and Maurice Maggs. All three have been introduced to readers in earlier pages of this volume.

The following subjects are covered in the printed document (Volume 2):

TOPOGRAPHICAL SURVEYS

Early motorways: the late fifties and early sixties
Developments since the early sixties

ROUTE ALIGNMENT

Introduction
Practice before the mid-fifties
Developments in the early years of motorway building
The initial impact of computers: early and mid-sixties
Late sixties and beyond: new approaches to design
Analytical methods used in optimisation
Optimisation for preliminary route location
Optimisation of the vertical profile
Optimisation of the horizontal alignment
Why did optimisation fail to catch on?
Conclusion

ROAD LAYOUT STANDARDS

Early specifications covering geometric design
Highway Link design
Decisions on road type and number of lanes
Cross section details and dimensions
Junction layouts
Conclusion