The bridge clearance height , often just clearance height , is a term used in road traffic and shipping , especially on inland waterways , which describes the maximum vehicle height permitted under the existing German regulations for the passage of bridges or other structural facilities on or above the traffic route for road vehicles or . watercraft referred. The clearance height regularly takes into account a safety distance to the lower edge of the structure and is therefore lower than the actual clear height . Internationally and even in Europe, this is not the same.
This dimension is irrelevant for operation in rail traffic , since the clearance profile on the rail side must be adhered to for all vehicles at all times, on the open route, under bridges and in tunnels .
In Germany, bridges over motorways and federal highways are regularly built at least 4.50 m above the bridged road. A height of 4.70 m is generally required for the construction of new motorway bridges.
Accordingly, the German Road Traffic Licensing Regulations stipulate that the maximum height for motor vehicles , including the load, may be 4.00 m. In the case of vehicles that do not exceed the regular construction height when loaded, a non-displayed passable bridge height does not have to be particularly taken into account. Exceptions to this are special transports for particularly large goods, for which each section of the route must be checked individually beforehand with regard to passability.
Lower clearance heights may occur on roads outside of motorways and federal highways; these are indicated by the road traffic sign 265, in which the extent of the maximum permissible vehicle height is specified. The same applies to non-public structures (e.g. multi-storey car parks ) that have vehicle passages less than 4.50 meters high. The responsibility for displaying the clearance height lies with the owner of the structure.
In shipping, the bridge clearance height to be encountered is one of the factors that are decisive for whether a ship can drive under a bridge. The water level is mostly variable, the height of the ship's superstructure above the water level also depends on its respective loading depth , which in turn is influenced by the weight of the cargo and the fuel supply. Finally, the height of the bridges also depends on temperature changes, which can cause differences of up to 3.6 m in very large bridges such as the Verrazzano-Narrows Bridge . The skipper on an inland waterway or the vehicle driver on a sea waterway may therefore have to make calculations as to whether and when your ship can still pass the bridge. Even ships encountering stern waves can influence this decision.
The bridge clearance height is specified in the federal waterway map DBWK 1000 as a fixed value without variables. According to the legend on the map, it refers to the highest shipping or canal water level (HSW) , above which shipping must be stopped.
The Electronic Waterways Information Service ( ELWIS ) of the Federal Waterways and Shipping Administration contains the dimensions of locks and fairways and the maximum permitted ship sizes, in particular the bridge heights. Corresponding information is available for the Austrian part of the Danube at Via donau .
The specified static bridge clearance height in maps or lists via HSW takes into account the safety clearances, e.g. B. because of the slight curvature of many bridges, for inspection vehicles hanging under the bridges and other factors are necessary. In the case of arched bridges, the bridge level of the displays on site refers to the area of the marked passage width.
If individual bridges have lower clearance heights than usual on the route, this is indicated by a corresponding sign.
In everyday traffic with water levels well below the high water mark, the maximum permissible height of a ship above the water level must, if necessary, be calculated from the bridge clearance height plus the difference between the current water level and the HSW. This calculated permissible height must then be compared with the actual height of the ship, with the height of the ship resulting from its structural height above the keel minus the current loading depth, which in turn changes with increasing fuel consumption.
To make things easier, there are not only the gauges that show the current water levels , but also special bridge gauges with inverted scales that show the remaining headroom above the water level. At the Hamburg Köhlbrand Bridge there is a digitized bridge level on the girder with an accuracy of up to the 2nd digit after the decimal point (cm range).
Electronic devices such as the bridge scout have been developed especially for ships with lowerable wheelhouses , which warn of insufficient lowering or insufficient headroom.
The term clear height is simply meaningless for bridges over rivers and canals without bridge level, as long as it is not precisely stated which water level it refers to, and yet it is mostly misleading, as it refers to the actual lower edge of the roadway girder and does not take into account any safety distances.
Individual waterways and shipping authorities can publish continuously updated bridge clearance heights online, such as the Brandenburg waterway and shipping authority.
In rail transport , the dimensions of the so-called clearance profile apply to the entire route and thus also under bridges and in tunnels. It is determined by the respective railway company or the railway authority . For the Deutsche Bahn area , for example, the complex clearance profile specifies a minimum height of 4.8 meters for non-electrified routes and a minimum height of 5.25 meters for routes with electrical overhead lines . Correspondingly, a geometrically defined loading dimension or vehicle boundary profile that must not be exceeded is specified for the approved rail vehicles .
- vehicle 4.00 m + freedom of movement 0.25 m + safety space 0.25 m = 4.50 m (RAS-Q / RAA - guidelines for the construction of roads - cross-section / guidelines for the construction of highways )
- Ralph Holst, Karl Heinz Holst: Bridges made of reinforced concrete and prestressed concrete. Design, construction and calculation. 6th edition, Ernst & Sohn, Berlin 2014, ISBN 978-3-433-02953-4 , p. 162 ( digitized extracts on Google Books).
- D: StVZO ; A: (6) KFG ; CH: Art. 9 Para. 1 SVG Abs. 2
- Inland Waterways Regulations § 1.02
- Sea Shipping Regulations § 4
- DBWK 1000
- Electronic Waterways Information Service (ELWIS) ( Memento from 23 August 2016 in the Internet Archive ) of the Federal Waterways and Shipping Administration
- List of the Austrian Danube bridges on viadonau.org
- The water levels at certain levels can also be called up via ELWIS.
- Brandenburg Waterways and Shipping Office - bridge clearance heights
A collection of bridges with clearance heights of less than 4 m is available on Google Maps .
- Bridges and clearance heights under 4 m on Google Maps