Best way to model a city in UE4

Hello, I would like to create a city in UE4, I have the layout of the streets modeled in 3d already as well as the cad files, but when looking at tutorials online for UE4, they usually use splines for roads as it gives you the road markings and everything, but it’s not as exact as drawing it in 3d and importing as a static mesh, another issue is the size of that mesh is quite large, as a result the quality of the curves is very bad, what’s your suggestions for creating an exact city as i have in CAD, knowing that it has lots of curves as well as varying road sizes.