The AASHTO 17th Edition specification does not require bridge parapets to be dynamically tested, instead their performance is determined by calculation. Varley and Gulliver offer an aluminum design that is seen to be more aesthetically appealing over conventional systems. The companies calculations have been verified and approved by Arup consulting engineers.
The American standard has many similarities to the European standard EN 1317 but with the most notable differance being the impact angles and vehicle size. As an example EN 1317 uses a 1500kg vehicle impacting at 110km/h with an impact angle of 20 degrees for the N2 containment level vs NCHRP 350 with a 2000kg vehicle impacting at 100km/h with an impact angle of 25 degrees for the TL3 containment level. The difference in energy is huge with the NCHRP 350 imapct being over 50% higher than EN 1317. The American standard should be used where the majority of the vehicular population is larger than in Europe.