Editing Automatic Warning System (section)

=== Strowger–Hudd system ===
By the 1930s, other railway companies, under pressure from the [[Department for Transport|Ministry of Transport]], were considering systems of their own. A non-contact method based on [[Magnetic field|magnetic induction]] was preferred, to eliminate the problems caused by snowfall and day-to-day wear of the contacts which had been discovered in existing systems. The Strowger-Hudd system of Alfred Ernest Hudd ({{C.|1883}}{{Snd}}1958) used a pair of magnets, one a permanent magnet and one an electro-magnet, acting in sequence as the train passed over them. Hudd patented his invention and offered it for development to the [[Automatic Electric#England|Automatic Telephone Manufacturing Company]] of Liverpool (a subsidiary of the [[Automatic Electric|Strowger Automatic Telephone Exchange Company]] of Chicago, Illinois).<ref name=GG/><ref>{{cite patent |country=US|number= 1599470|status= |title= Railway Signalling System|pubdate= |gdate= 14 September 1926|fdate= |pridate= |inventor= Alfred Ernest Hudd|invent1= |invent2= |assign1= |assign2= |class= |url=}}</ref> It was tested by the [[Southern Railway (England)|Southern Railway]], [[London & North Eastern Railway]] and the [[London, Midland & Scottish Railway]] but these trials came to nothing.

In 1948 Hudd, now working for the LMS, equipped the [[London, Tilbury and Southend line]], a division of the LMS, with his system. It was successful and [[British Rail]]ways developed the mechanism further by providing a visual indication in the cab of the aspect of the last signal passed. In 1956, the Ministry of Transport evaluated the GWR, LTS and BR systems and selected the one developed by BR as standard for Britain's railways. This was in response to the [[Harrow & Wealdstone rail crash|Harrow & Wealdstone accident]] in 1952.<ref name=grsw>{{cite book|last1=Wilson|first1=G R S|title=Report on the Double Collision which occurred on 8th October, 1952, at Harrow and Wealdstone Station in the London Midland Region British Railways|date=12 June 1953|publisher=[[Office of Public Sector Information|HM Stationery Office]]|location=London|pages=25–29|oclc=24689450}}</ref>