Dublin's busiest bus route

IIRC Dublin Bus released a list of their busiest routes last year and 15 was on top, followed by 39a and 27

I'm a bit surprised the 41 isn't there given it was made into a 24 hour route a few years ago

Although that would probably have the effect of making the route less busy overall

Also I guess it has some competition from the Swords Express too

The 41 on its own as "load factor" measured, would definitely be up there. However, the statistics posted above include a single boarding onto that route. With a route like the 15, it is going to have many multiples of boardings throughout the route as it traverses both sides of the city.

The 41 is shared with the 41 B and C along the majority of its route, so this dilutes it even further, and the fact that it is on one side of the city only. It is an extremely busy bus all times of the day and in both directions.

Both very true, and I agree that simply measuring the "busiest" route doesn't accurately represent the start and end points of many commuters

If you're using farebox data then you're going to struggle. With the progressing simplification of the fare structure (not to mention taxsaver and rambler tickets) it's very difficult to gauge travelled distance without individual surveying. The best you could hope for would be if there were infrared boarding/alighting counters built into the buses, but if you're operating purely off the farebox then all you're going to have is the boarding locations and maybe some data on the short distance fare usage.

In any case, it's no surprise that the top 10 routes are all cross-city – yes, even the 46A counts as one as it singularily served North Circular Road as a major radius all of its own.