I thought Jazz FM was available on 102.2 Mhz in the London area. Maybe 'was' is the operative word here.
My understanding is thus: mobile DAB is currently compromised because we are still running the FM masts at full modulation and the DAB muliplexes are at very low ERP in order to avoid interfering with FM broadcasting.
Much the same happened with the switchover to DVB (digital video broadcasting - digital terrestrial TV).
Effectively we are spending ages and ages committing to the new technology simply to support the tiny minority of people who refuse to embrace DAB.
By the time DAB is sufficiently covered for in car usage we will probably have 5G mobile data with 3G and 4G filling in the 'holes' such that we can simply used internet IP radio on the move. And as such DAB will have been a right royal waste of time and money.