find best road based on geolocation

Hello i want to tell user that restaurant is about to come in 200-500 m please slow down.For implementing this my thought was:

1. Map all resturant to some point on some road?(Assuming this is done)
2. Find on which road using is traveling based on geolocation?

Now for second i need to find way to determine the road based on geolocation.Also i think i need to know the direction of road to determine road.

please suggest how can i achieve this.

After determining road and point on road , direction of road, i need a way to find the resturants point which are in the forward direction of the road.

Please suggest how can i do this using postgis and osm data