The Maps app lets you see any traffic problems on a planned route. Tap the ‘i‘ icon in the bottom right and choose the Show Traffic option (if it’s already on it will give you an option to Hide Traffic instead.)
This reveals traffic data on the map. Roads highlighted with an orange dashed line indicates that there is some traffic, while a red dashed line indicates severe traffic on the route.
Symbols show the location of roadworks and road or lane closures as well.