Is there a bus service between Watford Junction and Luton Airport ? is
there a timetable ?

Dear dogsbollocks-ga,

There is the Arriva bus 321 which operates between Watford Junction
and Luton Airport. The timetable is available on this link.
http://www.arriva.co.uk/__80256E280053B5B6.nsf/vWeb/flDNOS65CKZU/$File/gr321se0.pdf?Open
Please note that some of the buses do not run on schoolholidays.

This page will link you to a route map and additional information.
http://www.arriva.co.uk/__80256E280053B5B6.nsf/vWeb/wpDNOS65CKZT?Open&show=current&region=Shires%20and%20Essex&town=Watford%20Junction

I hope this answers your question. If it does not, or the answer is
unclear, then please ask for clarification of this research before
rating the answer. I shall respond to the clarification request as
soon as I receive it.
Thank you
answerfinder


Search Strategy
buses "watford junction" led me to the Arriva web site

If you aim to catch a plane at Luton Airport, then I would avoid the
321 bus like the plague.

The train service from St Albans to Luton is pretty reliable, there is
a dedicated bus service from Luton Airport train station to the actual
airport.

You can get from Watford Junction to the old St Albans station by a
funny little single track train that is also reliable, but crossing St
Albans is painful with any luggage, so you would need a taxi.

It is a long time since I've been on the 321, but my memories are not pleasant.

Thanks for that frde. 

dogsbollocks-ga, you will see on the route map referred to above where
the railway lines are located.
You can plan your journey here.
http://www.nationalrail.co.uk/

@AnswerFinder

I was impressed by your research
- just that I would not take a bus to an airport ...