Serpentine

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Serpentine on a mountainside in Chile
Serpentines of the hiking trail in the Saugasse

The term serpentine ( lat. Serpens , snake) describes a serpentine path or a path laid out in several narrow bends or a road of the same type on a mountain slope . The term is also sometimes used for the serpentine course of a river (see meander ) or canal.

development

The serpentine is the most natural way to conquer a slope, the steepness of which overburdens the performance of humans, animals or machines. Compared to a more direct connection, it extends the route many times over and thus makes it possible to overcome the same height difference with smaller inclines . For this reason, the serpentine has played an important role in road and path construction for a long time. Remains of simple serpentines in the Alpine region (such as the San Bernardino Pass or the Roman road near Obertauern ) attest to this.

With the advent of the automobile, driving on the old serpentines became an increasing problem. The narrow and poorly fortified turns, previously only used by humans or pack animals, often no longer met the requirements. As a result, attempts were made (especially in the case of important road links) to widen the existing hairpin bends and to pave the road better. As far as possible, new routes (often with engineering structures ) were built.

Despite all efforts to avoid serpentines, they are still necessary today. Worldwide they are used to develop mountain slopes or to overcome mountains or a steep coast . In some cases, serpentines are also characterized by a scenic route ( panorama road ), so that the function as an excursion and recreational road comes to the fore.

Alignment

Map of a turn

The routing of a serpentine turns out to be extremely demanding and requires extensive knowledge of road planning.

In contrast to the routing on the open road, the planning of a serpentine follows almost exclusively principles of driving geometry. This means in particular that no coordinated sequence of radii ( relative alignment ) is used, but rather the respective drag curves of the design vehicle are decisive. The main focus in the planning is on the individual turns of a serpentine. Each of these turns must be viewed separately from the other turns and planned separately.

When building turns, it has proven useful to insert a short opposite curve at the beginning and end. In this way, the imminent change of direction is made clearer to the vehicle driver. In the bend itself, a minimum radius of around 12.5 meters (roughly equivalent to an inner curve radius of 5.30 meters) should not be undercut. Very small radii also require a very large lane width due to the drag curve, whereby in the case of lower expected traffic density it is consciously accepted that many vehicles need the entire lane width in bends and then no vehicle encounters are possible there. Furthermore, the longitudinal slope in the bend should only be half as great as that of the distance between the bends.

Traffic safety

Bend with lane markings and crash barrier (Madeira)
Course of the priority road, additional sign at the bend of a serpentine (Germany)
Notweg at a hairpin bend (Austria)

From the point of view of the road user, the serpentine is an obstacle due to its unsteady course and at the same time represents a potential source of danger due to various factors. To drive through a serpentine, the vehicle driver may have to brake several times in succession, turn hard and then accelerate again. In many places, certain behaviors and rules of conduct have become established, such as sounding the horn in front of a confusing bend or the general priority of vehicles driving uphill, because the driver of a vehicle driving downhill usually can already see a piece of the road below the bend shortly before the bend so that oncoming vehicles can be recognized.

The problematic factors include, in particular, the steep longitudinal gradient, restrictions in the lane width and the associated risk of a collision with oncoming traffic. The general dangers of a mountain road, such as falling rocks , bad weather or limited visibility, as well as deviating from the road , often make things more difficult .

In order to make road users aware of these dangers, appropriate signs (speed limit, no overtaking, etc.) are usually attached. To make the road layout clearer and to better separate oncoming traffic, a lane marking is also available in many cases . Fall protection (crash barriers or concrete protective walls ) arranged on the side are intended to prevent falls when leaving the lane. In particular on serpentine stretches that can be used by trucks, there may also be emergency routes at regular intervals that serve as a run-off zone for vehicles traveling downhill with a defect in the braking system.

If a safe passage for certain types of vehicles (such as buses or trucks) cannot be guaranteed due to too narrow radii or too narrow a lane width, a route closure for these vehicles is often ordered.

Web links

Commons : Serpentine  - collection of images, videos and audio files
Wiktionary: Serpentine  - explanations of meanings, word origins, synonyms, translations

Individual evidence

  1. ^ Friedrich Kluge: Etymological Dictionary of the German Language , 22nd edition, Walter de Gruyter Verlag, 1989
  2. ^ Pierer's Universal-Lexikon, Volume 15. Altenburg 1862, p. 892.
  3. P. Petrovic: The turn in mountain road construction , Springer-Verlag, 1967, page 1
  4. ^ Knaur, The German Dictionary, Lexicographical Institute Munich, 1985, page 881
  5. ^ A b Günter Wolf: Street planning . Werner Verlag, Munich 2005, ISBN 3-8041-5003-9 , pp. 197 .
  6. P. Petrovic: The turn in mountain road construction , Springer-Verlag, 1967, page 5