transition from old town

I am building a European-style city, and now I have a problem. I built the entirety of the old town; now, the only thing to do is to start making the modern type of city. But I don't know how to transition from the old style to the modern.

https://preview.redd.it/i9wti9k4xu3h1.png?width=1285&format=png&auto=webp&s=a8558f49e75024567a8951f175599c301602a7e3

https://preview.redd.it/l7x2wokzwu3h1.png?width=1463&format=png&auto=webp&s=9c7afb94a2f41e08d3977bbfdd496e5b0896a464