The sub strata was a reason at one time but more modern methods of tunnelling and tunnel wall construction overcame what was seen as problems at earlier times.
In mid 1948 the City Surveyor investigated the possibility of a subterranean railway, similar to London's 'tube' system. This would be a line serving the north eastern part of the city: Perry Barr, Aston, Erdington and Kingstanding. After extensive studies of the London systems (there are more than one, being just sub surface and much deeper (tube)) a scheme for an eleven mile system has been developed. Apparently stations were considered at Aston Cross, Salford Bridge, Erdington High Street, Perry Common, Kingstanding, Perry Barr and Hockley. These stations would be served by trains every ten minutes with a five minute interval at peak times with a fair, on average (at the time of 4d. (2p). It was believed that 57,000 people would use these trains each day.
The projected cost of construction was given as £13.75 million with annual income of £350,000 which coupled with loan charges and operating costs gave the cities transport coffers an annual deficit of £831,800 Needless to say the scheme was abandoned.
This year (1948) was a difficult one for the transport committee. New buses on order (785)were slow in delivery - only 210 being received by July. The Stechford trams would be replaced by buses in October and it was decided that the Moseley Road routes would be next to go. That occurred in October 1949.
Despite a petition for free bus passed for the aged it was not felt necessary and had to wait a few more years.
Actually Birmingham was over 40 years ahead in granting this type of bus pass compared to other areas of the UK.