Train passengers have indicated a broad improvement in rail services from Hemel Hempstead, Berkhamsted and Tring.
London Midland runs the route from Northampton to London Euston, as well as other branch lines and some regional services.
In the latest National Rail Passenger Survey (NRPS) passengers gave the company an overall satisfaction rating of 86 per cent.
This was the same rating as 12 months ago, and a two per cent improvement compared to last autumn’s survey, which covers 26 train companies across the UK.
Over the last six months London Midland’s sharpest improvement in customer satisfaction was for its toilet facilities - although still only 49 per cent of passengers rated them as Satisfactory or Good.
Rail-users were most likely to be unhappy about car parking facilities. Almost one third - 32 per cent - gave a rating of Dissatisfied or Poor.
Richard Brooks, commercial director at London Midland said: “We would like to thank our passengers for telling us that they are continuing to see an improving service from London Midland. This is our fourth year-on-year improvement in customer satisfaction.
“We are not complacent however and we are committed to making further improvements. Over the next 12 months we will be investing a further £15million on the things that really matter to our passengers. This includes improved cleanliness and making it easier and simpler to get information, buy tickets and travel with London Midland.”