For the transportation update I would suggest first and foremost a new statistic for bicycle usage in normal democracy 4 bicycle policies evenly reduce car usage, bus usage, as well as rail usage. I find this unrealistic as bicycle usage increasing likely would not impact rail usage at all decrease bus usage a more moderate amount while reducing car usage the most.

In VF's industrial economics there is a policy for, I forget exactly what the policy is called, something like urban planning paradigm. With that policy you can on one side set it to have depaving initiatives while on the other side you can set it to have your urban planning have sprawling suburbia. While you are updating for your Transportation update I hope you consider these ideas. The transportation overhaul mod is also a great mod to look to for inspiration although they have a problem with introducing just a ton of new policies and making it very hard to deal with the bureaucracy.