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Routing inconsistency in FAST mode (A→B vs B→A distance difference)

Symptom

A significant difference in distance and travel time is observed between two points depending on the routing direction:

  • A → B: short distance (~56 km)
  • B → A: much longer distance (~97 km)

The issue occurs only when using:

routingMode=FAST

 When using:

routingMode=SHORT

the results are consistent and symmetrical.

 

Cause

<This behavior is expected and related to how the FAST routing mode works.

 FAST mode optimizes travel time, not distance

The route calculation depends on multiple factors:

  • Road network hierarchy
  • Speed profiles per road type
  • Access to major roads (highways, main roads)
  • Directional constraints (one-way streets, restricted turns, entry/exit points)

The road network is not symmetrical

An optimal route in one direction is not necessarily optimal in the opposite direction.

In certain areas (e.g. urban zones, bridges, highway access points), this may result in:

  • A direct route in one direction
  • A longer detour in the opposite direction, which is still considered faster

This is expected behavior and not a bug. 

 

Resolution

Adjust the routing mode according to your business needs:

 Use case 1: Reliable and consistent distance

routingMode=SHORT

 Use case 2: Optimized travel time (ETA)

routingMode=FAST

 Practical recommendation

  • Identify the business requirement:
    • Distance accuracy → SHORT
    • Travel time / ETA → FAST
  • Avoid using FAST mode as a reference for distance
  • If needed, compare both modes to validate results for your use case

 

Related articles

Short and Fast Routes
Short and Fast Routes - code sample
A-B Routing

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