A quick tip on how to show in a filter only the relevant values related to a parameter or another filter. 

When you select a Borough on the  ‘Choose a Borough’ parameter a list of all the bus will shown.

In order to show just the bus routes related to your Borough you click on the little arrow, below the X of your filter ‘Choose a Route’ and select ‘Only Relevant Value’.  Here is just the list of the bus routes going through Barking and Dagenham!