@MichealYun To upgrade a new piece of road to streetcar avenue from scratch costs only 7500 for the smallest section which is half the width of a residential building and you can do this in stages to suit your available cash.
Basic road is free
Four lane upgrade 300
Six lane upgrade 1200
Avenue upgrade 1500
Boulevard upgrade 2000
Streetcar Avenue upgrade 2500
Total 7500
The same piece of cobblestone road costs 10000 payable in one chunk.
Surely it would have been fairer to treat the cobblestone road as just a basic free road to be used in those areas where the standard road spoils the effect. It doesn’t need to be anything special just a piece of road in keeping with the buildings alongside it.