When a journey begins or ends away from a road, we 'snap' to the nearest node on the road network. How this works can be adjusted using the two snapping parameters:
snapping.penalty
When enabled (as is the default), the walking time and distance from the departure location to the nearest road, and from the nearest road to the arrival location, are added to the total travel time and distance of a journey.
When disabled, these walking times and distances are not added to the total reported values (i.e the journey effectively starts and ends at the nearest points on the road network).
Other mapping providers (such as Google Maps) don't typically include a snapping penalty.
snapping.accept_roads
When set as both_drivable_and_walkable (the default), the journey can only start or end on roads that are accessible by both cars and pedestrians. This effectively means journeys can not start / end on motorways.
When set as any_drivable, the journey can start or end on any road accessible by a car (including motorways).
Other mapping providers (such as Google Maps) typically allow snapping to all roads, including motorways.
The maximum snapping distance is 500m - locations further away than this from the nearest point in the road network will be marked as Unreachable.