Postgres SQL - Top 2 records GROUP BY and COUNT

I have a some data in the following format:

I want to count the Routes and then show only the most popular 2, grouped by Bus :

I have the following so far:

SELECT Bus, Route, COUNT(Route) 
FROM my_table
GROUP BY Bus, Route
ORDER BY Bus, COUNT DESC

I have looked at Rank / Partition /Limit but I can't get the COUNT field to work, nor can I work out the correct syntax.

Group and count (ti) then order/assign position by bus (tx) and select these with position <= 2.

select bus, route, cnt
from
(
  select *, row_number() over (partition by bus order by cnt desc) r
  from 
  (
    select bus, route, count(*) cnt 
    from the_table
    group by bus, route
  ) ti 
) tx
where r <= 2;

SQL fiddle

The same using ti and tx as CTEs, maybe cleaner and more readable:

with ti as
(
  select bus, route, count(*) cnt from the_table group by bus, route
), 
tx as
(
  select *, row_number() over (partition by bus order by cnt desc) r from ti
)
select bus, route, cnt from tx
where r <= 2;

Edit
If you need the result with ties then use dense_rank() instead of row_number().