Slowest Passenger Route

[Buttsy]

I'd say that it would be reasonable to contend that Bere Alston - Gunnislake is a separate route as it is/was a branch off the LSWR Plymouth - Exeter main line. Despite what it says in the timetable I'm not sure how it can only take 20/21 mins for a 4.5 mile journey though as this assumes an average speed of 13.5mph, with a max line speed of 20mph and a stop at Calstock.

The reason it takes so long is that it was built under a light railway order and the maximum speed is 25mph under such an order (most preserved railways run at this speed). It is unlikely that line speed will be increased due to teh large number of unprotected level crossings on the route which would be expensive to protect for what would be a small saving in journey time.
The best way to speed up the route would be to increase the line speed from Bere Alston to Calstock, a lot of which is at 10mph with no crossings.

 

[Unixman]

The Cambrian is always a good bet ... 2 1/4 hours to cover the 57 miles from Mach to Pwllheli .... Just over 25 mph. This must be the slowest for any service that travels a reasonable distance!

 

[cjohnson]

Balham to West Croydon via Crystal Palace always seems incredibly slow

Unless I've got my sums wrong, another slow one on the Southern is London Bridge-West Croydon via Streatham. 42 minutes to cover just over 12 miles = approx 17mph.

 

[CheapAndNerdy]

Balham to West Croydon via Crystal Palace always seems incredibly slow:
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Average speed: maybe 30 mph?

I did the reverse journey on a whim and was caught out by its slow progress and ended up breaching the Oyster maximum journey time (from Whitechapel).
I measured 7.3 miles using Google Maps. With a journey time of 25 minutes, that makes just over 17mph!