Maximum crossfall (superelevation)

superelevation 01

In an earlier post on minimum crossfall (see here) I wrote that “Depending on which design guideline you read, the minimum crossfall can vary depending on features such as:

  1. Traffic flow
  2. Material used for the road surface
  3. Whether the road is paved or unpaved
  4. Traffic lane (inner or outer)
  5. Layer of the road pavement
  6. Year the design guideline was published
  7. Country which published the design guideline
  8. The particular guideline (two guidelines from the same country may propose different figures)
  9. Type of traffic running along the road surface
  10. Type of terrain
  11. Design speed
  12. Dominant type of weather
  13. Module (element) of the road cross-section (e.g. carriageway, shoulder)
  14. Highway section type (at-grade road, road in tunnel etc)
  15. Longitudinal gradient”

For most of these features the blog post provided some figures for minimum crossfall. Similar features can be found in relation to  values for maximum  crossfall(superelevation). We could even add two more features:

  1. Type of environment (e.g. urban or rural)
  2. Road class

Some values for maximum crossfall (superelevation) for many of these features are given below.

There are other considerations which should affect the selection of a value for superelevation. For example (ref. 857) says that the value of superelevation chosen should allow for:

  • safety
  • comfort
  • appearance
  • operating design speed of the curve
  • tendency of very slow moving vehicles to track towards the centre
  • stability of high laden commercial vehicles;
  • difference between inner and outer formation levels
  • length available to introduce the necessary superelevation

Values

The following tables list values for superelevation for differerent features. They have been taken from a number of sources.

superelevation 02

And

superelevation 03

And

superelevation 04

And

superelevation 05

Comment

First, there seem to be many “features” which can affect the value of superelevation to be selected (the notes above list 25 of them). Perhaps some are already covered, at least in part, by others; and perhaps some are only secondary. But even if the key features could be reduced to (say) 15, surely every textbook and design manual should list all of them in its notes on superelevation. If not, then perhaps either the manual is incomplete; or it does contain the information but spreads it through different pages and sections of the document (making it difficult to find).

References

148 – South Africa, CSIR “Geometric design guide” 2002

255 – UK, Highways Agency “DMRB TD 9/93 highway link design” 2002

710 – Australia, Queensland Government “RPDM road planning and design manual chapter 11 – horizontal alignment” 2002

744 – UK, DTp “DMRB TA 90-05”, 2005

831 – USA, AASHTO “A policy on the geometric design of highways and streets” 2011

846 – Bhutan,  Ministry of Works and Human Settlement, “Road classification guidelines” 2009

857 – Australia, Austroads “Rural road design (8th ed.)” 2003

985 – USA, AASHTO, „AASHTO Bike design guide“ 1999

1023 – Germany, Hessische Straßen- und Verkehrsverwaltung „Leitfaden Unbehinderte Mobilitaet für Blinde“ 2006

1060 – South Sudan, Ministry of roads and bridges “South Sudan, Low volume roads design manual” 2013

1063 – Ethiopia, Ethiopian Roads Authority, “Ethiopia, geometric design manual 2002 (version 2)”

1115 – Estonia, Estonian Road Administration, “Estonia Norms and Requirements of Road Design” 2000

1132 – Switzerland, Schweizerische Fachstelle für behindertengerechtes, „Baue Strassen – Wege – Plaetze, Richtlinien für behindertengerechte Fusswegnetze“ 2003

1161 – New Zealand, Land Transport NZ, “Pedestrian planning and design guide” 2007

1190 – Ireland, NRA “TD9 – Road link design” 2012

1200 – Italy, Ministerio delle Infrastrutture e dei Trasporti „Norme funzionali e geometriche per la costruzione delle strade“ 2001

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About roadnotes

Robert Bartlett is an international consultant with over 30 years of professional experience as a highway and traffic engineer with leading companies and organisations in several countries, including Germany, China (Hong Kong), Qatar and the UK. Specialised in urban studies, transport and the use of GIS, research has included new ideas on subjects such as the study of social justice using GIS, the dimensions of vehicles, and comparative geometrics (highways and transport).
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