40-YEAR DESIGN LIFE

Hitherto, the stage construction approach has been adopted for asphalt roads in the UK. However, traffic volumes have increased so much during recent years that user delay costs have become much more significant. For the roads with the heaviest traffic, user delay costs tend to dominate a whole-life cost assessment. For these roads, this additional cost makes a 40-year design life before strengthening the most cost-effective option. Restrictions are being removed from contractors, enabling them to produce a higher-quality pavement. The joint HA/BACM/RBA research programme of the mid-1980s has developed Heavy Duty Macadam (HDM), Dense Bitumen Macadam (DBM), and DBM50 as new materials, with substantially higher stiffness than conventional roadbase materials. Since then, there have also been evaluations of High Modulus Asphalt (EME), a new French roadbase material, and DBM15 at the Transport Research Laboratory (TRL). For the roads with heaviest traffic, HMB roadbase can clearly be shown to be cost-effective for 40-year asphalt designs, but, for most roads, stage construction of asphalt roads, using traditional materials, will still be the most cost-effective approach. For the covering abstract, see IRRD 889137.