text: Ah yes, this was me a few years ago – I tried to make better sense of the routing by applying the trunk vs primary logic on https://wiki.openstreetmap.org/wiki/Roads_in_the_United_Kingdom (based on road number signage being in either green [trunk] or white [primary]). On signage it appears this is still the case, and so the classifications here are *technically* correct.
  
  However looking at Sabre, the suggestion is that neither the A20 nor A21 pass through the town centre any more, as currently mapped, and instead the A21 uses the stretch you highlight @VictorIE, with both routes using the southern bypass. In theory that would mean all the current town centre trunk routing could have its numbering removed and be altered to highway=tertiary. I'd be fine with all that **except** it appears the A20 is still signposted through the town centre, and the A21 from High Street/South Street junction southwards. So removing those refs and classifications means that GPS's would not be acknowledging what drivers see on signage. Although we *could* pretend that all these signs have the road numbers in brackets.
  
  Additionally, the only legislation I can find is from 1998 https://www.legislation.gov.uk/nisr/1998/318/schedule/made (predating the bypass) stating the A20 and T11 trunk route go through the centre.
  
  So I'm not sure. The above is an option, or perhaps keep the town centre routing with existing numbering (meaning the A20 still takes 2 routes, one through centre and one via bypass), but downgrade centre routing to Primary? Then upgrade the section of Portaferry Road to trunk?