Allowing either the US or European criterion to be used will provide economic benefit for the local road authority through increased competition. Since both testing criteria require basically the same light car test (820 kg vehicle – plus dummy weight in NCHRP 350 and 900 kg vehicle including dummy weight in EN 1317-2, 100km/h and 20 degree impact angle) the limiting factors will be the impact severity of the capacity test and the anticipate number of high center of gravity vehicles. A longitudinal barrier that meets EN 1317-2 or NCHRP 350 should be allowed to be used provided the capacity test impact severity of the barrier is higher than the capacity test impact severity of the specified longitudinal barrier. The impact severities of the different levels of barriers in EN 1317-2 and NCHRP 350 are shown in Chart 1 below.
Chart 1 - Comparison of Impact Severity Levels
(click chart to enlarge)For example, if a road authority decides the most appropriate longitudinal barrier for a road should be the EN 1317-2 “N-2” classification, then any barrier that has an impact severity greater than 81 kilojoules should be allowed as well. This means NCHRP 350 Test Levels 3, 4, 5 or 6 as well as EN 1317-2 Test Levels N-2, L-1, L-2, L-3, L-4a or L-4b also could be used on this project.
If accepted at the upcoming Annual Meeting in January in Washington DC, The TRB AFB20(2) Roadside Safety Subcommittee on International Research would strongly recommend that all road agencies require that longitudinal barriers meet the minimum performance standards as outlined in EN 1317-2 OR in NCHRP 350. A safety factor should be included when determining the severity level to be specified. If a significant number of trucks are anticipated on the road, a higher center of gravity barrier should be specified. Furthermore, the TRB AFB20(2) Roadside Safety Subcommittee on International Research would recommend that impact severity levels be used to specify the minimum capacity for a longitudinal barrier and that any barrier with a higher impact severity level be allowed to be bid on the project regardless if the longitudinal barrier has been tested to EN 1317-2 or NCHRP 350.
3 comments:
My colleague Dr Victoria Gitelman and I have done quite a lot of work on the issue of compatibility between NCHRP 350 and EN 1317-2 because here in Israel we have gone along this path of coming to a decision to accept devices that fulfill either of the two test procedures.
We have a few comments on your document as it stands.
We totally accept the view that the two documents are fairly similar and thus we officially accept devices that are tested according to either procedure.
We generally decide on the level of barrier selected as appropriate for conditions on the basis of the relevant test conditions, i.e vehicle weight, velocity, angle of impact. Thus we consider H-1, which contains a 10 ton truck as better suited to more severe conditions, i.e on divided highways than a TL-3 barrier- which contains a pick-up truck. We also look at the ASI which is not a limiting condition in NCHRP 350. We term ASI as crash severity and not the energy levels as you suggest.
Thus we have problems with accepting the heavy reliance on energy levels as the most relevant criterion.
I also find it strange that a TL-4 barrier has a lower impact severity level than a TL-3 barrier. This may also be related to the question of how an H-1 device(containing a 10 to truck) has a lower ISL than a TL-3 device.
I'm afraid that I cant really agree with the approach. Whilst I would fully support that countries only install barriers to a National or European standard, it may be dangerous to restrict this to EN1317 and NCHRP 350 as this might deter others from developing other standards, which may be to the benefit to us all.
In addition, the process of using the impact severity level (I/S) will negate the complex interaction between barrier and vehicle, in which the dimensions of the vehicle can greatly effect the results of a test, both in terms of containment, severity and displacement. We have seen, during testing, that due to the differences in the height of the centre of gravity and bumper (and therefore height of interaction between the barrier and the vehicle), differences in results often occur. In addition, the evaluation criteria between the two standards also differ in some aspects and, in some cases, I have seen tests presented as being acceptable at past TRBs which would be unlikely to meet the requirements of EN1317 !
I look forward to a fruitful and interesting discussion on these elements at the forthcoming TRB !
Gavin Williams
Head of TRL's Vehicle Restraint Systems (VRS) Team
TRL Ltd.
Crowthorne House
Nine Mile Ride
Wokingham
Berkshire RG40 3GA
UNITED KINGDOM
It is appropriate that safety barrier systems be tested to accepted world wide standards. It is, therefore, appropriate to use the test results from either NCHRP350 or EN1317-2 to evaluate a barrier system. However, It is also appropriate that one barrier system be fairly judged against another and so there is a need to be consistent when comparing barrier systems.
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