They are all correct. There is not one "right" answer in geometric design, but a range of correct answers. Your definition of paradigm is incomplete; a better definition is "a set of practices the define a scientific discipline at any particular period in time WITHIN A UNIQUE GEOGRAPHIC, CULTURAL, AND SOCIAL CONTEXT...."

Geometric design isn't a "one size fits all", but the design that is the safest and most commonly accepted for the drivers in a region. There are theoretically superior geometric designs in Europe and Australia that will not work in North America because the lack of familiarity of the design will cause confusion to the motorists, and vice versa.

I don't think they are all correct (the various but comparable but different values for parameters such as minimum horizontal radius can't all be right). At the same time I think that there are some features such as side friction or superelevation where values are applicable to any culture or social context. Also, most t design sets already cover different geographic conditions, and geographic conditions vary regardless of society.

Unique geographic, cultural and social context

This would suggest (for example) use of the AASHTO Green Book details should be banned in any country other than the USA; multi-country standards such as the Asian Highway standards should be cancelled (possibly not a bad idea, but for other reasons), and countries such as the republic of Ireland are wrong when they more or less adopt directly another country's highway design standards, even if their culture is different.

Theoretically superior geometric designs in Europe and Australia that will not work in North America....

But the US introduced roundabouts (a European idea). A country won't progress much if it rejects superior designs as a matter of principle. Conversely, if a country's current design method is weak then they should move away from it.

Lack of familiarity of the design will cause confusion to the motorists

This would be bad news for Europe, where drivers from one country should then be prevented from driving in any other country because of this lack of familiarity of the design.

My basic arguments are

First, that there are certain design parameters or areas which are globally applicable (much the same as the conventional formula linking horizontal radius to speed, friction and superelevation seems to be - rightly or wrongly - almost globally applied). There may even be some types of road (e.g. with a design speed over around 70 km/hr) which are globally valid, and not subject to cultural or social context. Lower speed roads such as city streets may well be influenced by culture and society (or at least, they should be) - so local design guides such as Dehli's "Street design guidelines" may be a good step - but even for these roads, some parameters such as crossfall are likely to be "universal" values. More generally, where highway design guidelines differ (Australian, German, US etc) the arguments for these differences are in abstract engineering terms rather than in geographic, cultural and social terms.

Second, that geometric design standards are "sets". By this I mean that you cannot mix and match between design standards, taking (say) values for design speed as adjusted by Norway, plus values for superelevation from the USA and values for side friction from Australia.

Third, that the different sets of highway design standards are generally developed through abstract engineering concepts, that these concepts often produce different results (minimum horizontal radius perhaps), and that not all the concepts are equally good - so engineers should take the best ones and develop them further (how is it that Austroads considera side friction values separately for goods vehicles and cars, but few other countries do).

Arguably the ideal would be for best practice design to be applied everywhere, with suitable modifications such as to streetscapes or bicycle lane widths to allow for local practice. I think a bigger problem is that some of the basic concepts for highway design (such as perhaps the formula linking horizontal radius to speed, friction and superelevation) are weak to unproven. A better foundation for highway design should be developed, and this better foundation should be given a wide application.

One problem with identifying "best practice" is that many design standards are only available in "foreign" languages (such as Norwegian or German) and so their innovative ideas are not available to the global community.

As vehicles become more interchangeable from nation to nation,

our roadways will tend to become more standardized as to width,

super-elevation, speeds, and possibly safety devices, etc.

What I doubt will ever become standardized is roadway striping.

Currently, the US has 50 states, and it has 50 different construction

standards for standardized items. State standards are always

evolving just as cars are always evolving, and cities evolve.

Fortunately some states are now putting their standards on-line so

access is fairly easy.

I noticed that most US states also have their own road design manuals, whilst much of the rest of the world seems to treat the US organisation AASHTO's green book as "the" design manual. If the US states don't give the book this status, then perhaps neither should anyone else.

The AASHTO Green Book ( American Association of State Highway and

Transportation Officials ) is a Book that evolves with time, and each

edition will have something new, or an elaboration upon prior design

concepts. Since more than one state contributes information to the

Book, and it has evolved by committees of committees and more

committees, it will always be in flux, as the Engineers in power at

the time make changes for whatever particular reason.

The more than 50 Roadway design manuals each have a HISTORY

of evolution based on designs that may be anywhere from five years old

to more than 100 years old. ( or Older ).

In the extreme, the Standard Gage of a Railroad was derived from the

Romans, and the standard width of their War Chariots. Thus the

Standard Gage of 4 foot 8 1/2 inches came so the ruts in the

road ( stone pavement ) would be the same width and both wheels

would go in the ruts all over the Empire. The roadway for trains, thus

began with wooden rails and flanged wheels, which eventually due to

excessive failure of wooden rails became Iron Rails, and later became

steel Rails, but until recently, they kept the wooden ties ( now concrete ).

What is really interesting is to acquire design and construction

manuals from nearly a century ago, and look at the various pictures,

and drawings. The roadways could be of wood, concrete, brick,

rock, or cobblestone. They show horse drawn road graders,

and rollers powered by giant three wheeled steam engines.

Roadways evolved as technology evolved, and construction

equipment evolved. Many of the roadway features are now

based on increasing standards of expectation with regard to

safety features, and the evolution of safety features.

Designs of every Bridge and Roadway features have, and will

continue to evolve, and if something is better, cheaper, safer,

or more efficient, it will eventually be incorporated in state

design manuals, and may eventually be adopted into a future

edition of the AASHTO Green Book.

i think the best one is AASHTO policy in geometric design for highways and streets.. and this statement do not mean that the other specification is wrong..the specification is based on the characteristics of the community on which it is developed..regards 

I think AASTO specification is more reliable.

Since my detailed comments above I have continued to look at standards from different countries, and also at what parameters are used in road geometric design. Now I would agree with Mr. Schrader's comment that "Your definition of paradigm is incomplete; a better definition is "a set of practices the define a scientific discipline at any particular period in time WITHIN A UNIQUE GEOGRAPHIC, CULTURAL, AND SOCIAL CONTEXT" I take note of these terms in my project "listing highway parameters". But I think that most existing standards are based on administrative boundaries not geographic / topographic boundaries (for example, Peru has three types of geographical region and so should have three sets of design standards). And there seems to be another problem with existing standards, in that (even in one country such as the USA different standards have different definitions for the same design parameter.