Category Archives: basics

NMT in developing and developed countries

There is a page on the Internet (here) which lists different modes of transport, grouped under the headings of: Intermediate Means of Transport (IMT) Non-Motorised Transport Modes (NMT) The two lists partly contain the same modes, so they could be … Continue reading

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Road gradient – (1) definition and vehicle performance

Definition of gradient In terms of the vertical alignment of a road, one of the primary design parameters is gradient. A good definition of gradient is given in (ref. 148), which says:

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Words which are out of date (1) carriageway

Road engineers don’t really know what they are talking about – at least, not when they use words inconsistently, or where the meaning starts to fade away. Take for example the word “carriageway”. Definitions are not consistent, and what some … Continue reading

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Understanding road geometrics (2)

Road cross-sections are a form of picture to show technical information. The information they aim to show can vary, covering either location of utilities lines, road pavement structure, or the transverse composition of the road – lanes, footways, medians etc. … Continue reading

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Understanding road geometrics (1)

Selecting a suitable value for a geometric road design element – perhaps horizontal radius – isn’t always easy. The most common way design standards use to present their data is through many pages of text and tables. These often present … Continue reading

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Horizontal radius – more doubts about the conventional formula

Johan Granlund recently sent me two papers he has published which discuss horizontal radius (see references below).

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What do posted speed limits show?

Engineers might think that the posted speed limit is based either on the design speed or on a measure such as the 85th percentile speed of traffic on an existing road,, and that theposted speed “is a speed limitation …. … Continue reading

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Geometric parameters (2) modifying factors

In my last post I talked about geometric parameters and said that it would help if the writers of standards used a common layout to present the values they suggest for a particular parameter. The post used examples of data … Continue reading

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Geometric parameters (1) a question of layout

In the search for a suitable value for a geometric design parameter, it can often be a relief to find a simple table which seems to give the figure you are looking for. The trouble is that a simple table … Continue reading

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Minimum horizontal radius

What I used to believe Towards the end of 2012 I added a blog post on the basic formula for calculating horizontal radius (here). At that time I thought that the geometric design of roads was pretty much straight-forward. With … Continue reading

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