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BS EN 1317-1:1998 describes a Vehicle Parapet as a safety barrier that is installed on the edge of a bridge or on a retaining wall or similar structure where there is a vertical drop, and which may contain additional protection and restraint for pedestrians and other road users.


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Manufacturers have developed and tested parapets to meet the containment standards specified in the codes. Much of the earlier testing work was involved with achieving a parapet which would absorb the impact load and not deflect the vehicle back into the line of adjacent traffic. The weight of vehicle, speed of impact and angle of impact influence the behaviour of the parapet. Consequently a level of containment has been adopted to minimise the risk to traffic using the bridge (above and below the deck).
BS EN 1317-2 1998 specifies criteria for vehicle impact tests on parapets for various containment levels. The containment levels adopted by TD 19/06 (Design Manual for Roads and Bridges Volume 2, Section 2, Part 8) require testing to be carried out for various vehicles impacting the parapet at an angle of 20o.
The vehicle impact test criteria for various containment levels as follows :


Parapet Containment Level

Test Vehicle

Impact Speed

N1
Normal Containment (Formerly P2{80})

1.5t car
 

80 km/h
 

N2
Normal Containment Level (Formerly P1, P2{113} & P5)

1.5t car
 

110 km/h
 

H2
Higher Containment Level

13t bus
 

70 km/h
 

H4a
Very High Containment Level (Formerly P6)

30t Rigid HGV
 

65 km/h
 

 

 

Metal Parapets are designed and tested by manufactures who apply to the Highways Agency to be included on an Approved List. A copy of the "Highways Agency's Approved Road Restraint System List" can be obtained from their website http://www.dft.gov.uk/ha/standards/tech_info/en_1317_compliance.htm
TD19/06 is the current design standard which requires carrying out a risk assessment to identify the hazards and minimise the risks to the road users.
The risk assessment is documented by using an Excel spreadsheet, a copy of which can be obtained from the Highways Agency's website http://www.dft.gov.uk/ha/standards/tech_info/rrrap.htm
A user-guide is also available on the same web-page.

TD 19/06 also directs the designer to use BS 6779 and BS 7818 for the design of specific elements of parapets.
BS 6779: 1998 - Highway Parapets for Bridges and Other Structures.
Part 1: Metal Parapets for the provision of infill to parapets (see TD 19/06 clause 4.29, 4.39, 4.40)
Part 2: Concrete Parapets for the design of reinforced concrete parapets with some amendments (see TD 19/06 clauses 4.56 to 4.60)
Part 4: Reinforced and Unreinforced Masonry Parapets to assess the containment capacity of existing masonry parapets (see TD 19/06 clause 4.62)
BS 7818: 1995: Pedestrian Metal Parapets
This Standard is required for the manufacture and installation of pedestrian restraint systems until such times as the drafting of prEN 1317-6 is completed (see TD 19/06 clause 9.3).

Design Considerations


Information required to be supplied to metal parapet manufacturers is listed in TD19/06, namely:

  • Containment Level (N1, N2, H2, H4a);
  • Impact Severity Level (ISL) (Normally Class B);
  • Working Width Class (W1 to W5);
  • The height;
  • The length;

Concrete parapets are ideal for very high containment parapets due to their significant mass.
Steel parapets are generally the cheapest solution for the normal containment. This is significant if the site is prone to accidents and parapet maintenance is likely to be regular. The steelwork does however require painting and is usually pretreated with hot-dip galvanising.
Aluminium parapets do not require surface protection and maintenance costs will be reduced if the parapet does not require replacing through damage. The initial cost is however high and special attention to fixing bolts is required to prevent the parapets from being stolen for their high scrap value. Aluminium also provides a significant weight saving over the steel parapet. This is sometimes important for parapets on moving bridges.


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