DUBLIN, Aug 12 (Reuters) - Post-Brexit trade frictions have "significantly altered" freight traffic between Ireland and Britain and sparked a steep rise in volumes to and from Ireland and other European Union members, an Irish government agency report said on Thursday. The introduction of checks on some goods since neighbouring Britain left the EU"s trading orbit on Dec. 31 cut imports from Britain by 35% in the first five months of 2021 while the number of shipping routes to mainland Europe more than doubled. So-called roll-on/roll-off (RoRo) traffic between Irish and British ports was 20% lower in the second quarter compared to the same pre-coronavirus pandemic period in 2019 while volumes on Irish/EU routes were up 99% on 2019, the Irish Maritime Development Office (IMDO) said. Overall volumes were 0.2% lower than the second quarter of 2019, providing a more reliable comparison than previous quarters, which were distorted by pre-Brexit stockpiling and tough COVID-19 restrictions.The most significant factor behind the changes was traders abandoning the once-speedier British "land bridge" - where hauliers would take a short sea crossing between Dublin and Holyhead in Wales, drive across Britain and then take another ferry to mainland Europe. Many are shunning the route over concerns about delays and disruption due to new customs controls, the IMDO"s quarterly report found. "It is clear in the first six months since Brexit, the configuration of Irish RoRo traffic has been significantly altered," said the agency, which provides support to maritime businesses in Ireland, citing the new trading arrangements. Traffic between Irish and British ports now accounts for 67% of all Irish Ro-Ro volumes compared to 84% two years ago. Direct routes to the EU have doubled their share to 33%.This does not automatically imply greater trade with other EU member states, the IMDO said, but rather a reconfiguration of supply chains away from the UK land bridge. Freight traffic through ports in Northern Ireland also rose to the highest level since 2007 as hauliers who traditionally accessed markets in the English midlands and southeast via Dublin Port instead shipped goods directly from Northern Ireland. While some checks have been introduced on goods travelling from the rest of the United Kingdom into Northern Ireland, goods can travel freely the other way. However, before Brexit, shipping via Dublin was a speedier option for hauliers.