Have you also tried to link traffic Service to the starter project as described in the doc?
Create a project
To create a project, follow these steps:
Sign in to the HERE platform using your HERE account.
Open the Projects Manager from the launcher.
Click Create new project.
Enter a name for the project. Project names don’t have to be unique.
Enter a project ID. Project IDs must be unique within an organization and cannot be changed for the lifetime of the organization. Project IDs must be between 4 and 16 characters in length.
Optional: Enter a description.
Click Save.
On the Resources tab, select Services and then click Link a Service.
Search for the HERE Vector Tile - Traffic service and click Link.
Click Done.
I tried this but had no luck so far. At least traffic info is used during navigation at the moment on my side.