McDONALD, Wormley, 1840s - Railways
Your ancestor was definitely one of the earliest railway workers in East Hertfordshire. The first line anywhere in Hertfordshire ran from London (Euston) through Watford to Boxmoor in 1837, and opened through Tring to Birmingham in 1838. The Northern & Eastern Railway was next - starting at London (Liverpool Street) and opening as far as Broxbourne in 1840 - which is when the Wormley level crossing would have opened. The line extended to Harlow, Essex in 1841 and to Bishops Stortford and Cambridge in 1842. The line later became the Great Eastern. [Source: Industrial Archaeology in Hertfordshire]
I am not familiar with the railway literature - except to know that books on the railways - including their history are numerous and I am sure there will be several describing the line in some detail.
The 1850/1 Post Office Directory shows that Wormley was on the Eastern Counties Cambridge Railway and that a William Wiseman was at the "Star".
The 1881 census shows a James Everett, railway signalman, living at the Signal Box, Wharf Road, which is probably where your ancestor lived - and the level crossing is still there.
If you can add to the information given above tell me.