You need to work out what the nearest routable adress is. This works wonderfully with taxis here.
FWIW cul de sacs are an evil invention, and what you describe is a common routing problem. The rescue services here solved it by mandating addresses with geolocation and the nearest streets for every house around here. That failed me because everyone uses that official data that is convenient for fire truck rescue.
The issue was resolved by complaining to the Uber Maps team for 9 months until they removed their fake road block.
The work around in the interim was a combination of:
1. Writing a long description of how to access our property.
2. Trying to limit the distance an uber driver had to travel. <1km made it more likely for them to review the map and comment before driving. Dont ask me why.
3. Oscillating the drop off marker on the map to make it more likely that the driver was sent to our street at all, where we could wave at them to get them to drive beyond the psychological roadblock.
4. Attrition lead some drivers to remember my name, and just come straight to the property ignoring the map.
Any other mapping service delivered people to our property fine. Its just that Uber randomly blocked the end of our street. Meaning our street had no entrance.
Problem was that, uber has an exclusive relationship for delivery with one of our local supermarkets, and my wife doesnt drive and was stuck at home with an angry baby for the duration.
Due to this issue we did push the maximum amount of our orders through other delivery apps, probably taking significant income away from uber. But they have deliberately structured their support channels to be impossible to deal with.
As a Openstreetmap contributor I know it is a rather common mistake, it is very seldom support actually can edit the map like you can on http://osm.org sadly these mistakes are not always trivial. I have similar support tickets oldest one is from 2007.
FWIW cul de sacs are an evil invention, and what you describe is a common routing problem. The rescue services here solved it by mandating addresses with geolocation and the nearest streets for every house around here. That failed me because everyone uses that official data that is convenient for fire truck rescue.