The National Capital Authority is preparing to slap reduced speed limits on roads in the parliamentary zone as it moves to prioritise riders and walkers over car users.

The authority said on Friday that reduced speed limits of 50km/h or 40km/h were highly likely to be imposed as motorists are relegated to the bottom of the transport heap in Canberra's national precinct. NCA chief executive Gary Rake said proposed changes to speed limits and crossings would be decided by mid-2013.

Mr Rake said community consultation was only likely to occur if the changes were considered major.

''At this point all we've decided is that we have that hierarchy for transport and we'll start to do a bit of analysis,'' he said.

''We'll look at where footpaths don't connect with another footpath on the other side of the road.

''We'll look at pedestrian crossings and the traffic speed limit - this will be the first thing we'll assess and we'll have that done in the first half of 2013.''

Mr Rake said it was highly likely that all roads within the parliamentary zone would have their speed limits reduced from 60km/h.

''There's a lot of data showing that pedestrians are less likely to sustain injury if cars are going slower,'' he said.''We will look at lowering the speed limit on King Edward Terrace, King George Terrace, Queen Victoria Terrace and the roads running off those.

''The ACT government recently trialled 40km/h zones in the busiest parts of the town centres and I understand they've decided to keep those in place and extend the trial.

''When we think of the parliamentary zone there are a lot of similarities to those areas.

''There's a lot of people around, it's not intended as a high-speed thoroughfare, there's lots of visitors moving around and, in our case, also a lot of schoolchildren.''

Mr Rake said the traffic study would consider where footpaths needed to be improved or added and whether traffic lights or new pedestrian crossings should be installed in some areas.

He said no new bike paths were planned.

The NCA's assessment would look at adding more parking spaces in the triangle for bikes.

''It's not about making exclusions for cars, bikes or pedestrians, it's about reprioritising who we prioritise first,'' he said.

''One side effect that people might find surprising is that the design speed of the road governs how far back the trees need to be.

''So the faster the road the further back trees need to be.

''By lowering the speed of the road we can keep trees close to the roads and paths, creating a shady environment in summer.''