Both ideas essentially taken from TomTom but in daily driving an absolute necessity.
Avoid next [distance]
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In case of a road block or traffic jam it would be great if it were possible to avoid a set distance from the current GPS location extending to the requested distance along the planned route.
Avoid part of route
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Similarly it would also be great if it were possible to avoid specific roads used along the route. So a UI that shows an overview of the route by roads/turns, allowing you to select a road and avoid it.