No one in their right mind would ever suggest that trams are capable of replacing all other travel modes. After all about a fifth of journeys are walked (because they are short). Similarly only 25% of trips are over 5miles long and less than 3% over 30miles.
BUT car trips (until coronavirus) dominated all trips, even in Bath, where nearly 70% are made by car and less than 10% by bus. Other European cities have shown that public transport usage can be increase to over 20% of the market, not by low fares or free services but by opting for or expanding tram systems, which passengers prefer. There are many examples from France and Germany that show tram + bus can get over 20% of modal split, and car reduced to under 40%.
It would be naive to think this could be achieved in Bath, certainly not in the short term. Many European cities have also promoted and got large increases in cycle trips but that might be impractical in Bath with the steep hills, even with electric bikes, and without separated and safe (perception) cycle routes.
Being realistic a new tram route in Bath should be able to attract 20% of the car trips in the corridor served. More lines provide a synergy for increasing further trip attraction, just like the underground in London which has a lot of interchange between lines. Trams give about 90% of the benefits of Metros, at a much lower cost, typically about 10% of the CAPEX. Think of the cost of Cross Rail in London, that spent on trams would have provided a network of over 500 miles, twice as long as the tube system.
In Bath getting progressively more lines and more car trips attracted will increase the public transport modal share and reduce car traffic, congestion and toxic pollution. The question is how can this be achieved ? WECA is obviously going to spent most of its money in Bristol. How do you think Bath can solve the problems of traffic congestion and toxic air pollution ?
PS there is a lot more in “Light Rail Developers’ Handbook” ISBN 978 1 60427 048 8, and great for insomniacs.