Speed value for ETA and Isoline calculation for cars and trucks
Symptoms
--------
Customers may report one or more of the following:
ETA values change depending on current traffic conditions.
Isoline ranges appear larger or smaller than expected.
Routes starting in the past still use current traffic conditions for part of the calculation.
Different ETA results are returned when real-time traffic is unavailable.
Time-dependent routing results vary between vehicle profiles such as car and truck.
Travel time estimates do not match a simple speed-limit calculation.
Answer
------
ETA and isoline calculations use multiple speed sources depending on vehicle type, route timing, and traffic data availability. The routing engine prioritizes Real-Time Traffic (RTT) data when available and automatically falls back to historical traffic patterns or map-based reference speeds if traffic information is unavailable. This behavior is expected and helps provide the most realistic travel-time estimation possible.
How Speed Values Are Selected
-----------------------------
### Priority Order for Speed Calculation
For both ETA and isoline calculations, the routing engine uses the following hierarchy:
1. Real-Time Traffic (RTT)
* Used for route segments occurring during the current time period when RTT data is available.
* Provides the most accurate representation of current road conditions.
2. Traffic Patterns
* Used when RTT is unavailable.
* Based on historical traffic behavior by:
+ Day of week
+ Month of year
+ 15-minute time intervals
* Holiday traffic patterns are applied in supported countries.
3. Reference Speed
* Used when neither RTT nor Traffic Pattern data is available.
* Derived from:
+ Functional Class (FC)
+ Speed Category
+ Country-specific speed modeling
### Example
If a routing request covers a journey lasting approximately five hours and the route start time was two hours ago, the routing engine can still apply current Real-Time Traffic data to the portion of the trip that corresponds to the present time.
Additional Details
------------------
### Free Flow Speed
For road segments with Functional Class (FC) 1 through FC4:
Free Flow Speed from traffic patterns represents the best achievable speed observed for that segment during the day.
For FC5 roads:
Speed values are calculated using Functional Class, Speed Category, and country-specific information rather than Free Flow Speed values.
### Car and Truck Routing
The same traffic-data hierarchy applies to both vehicle types. However, resulting travel times may differ because the routing engine also considers vehicle-specific routing rules and speed models associated with car and truck profiles.
Impact
------
Understanding the speed-source hierarchy helps explain:
ETA differences between requests.
Variations in isoline coverage areas.
Differences between car and truck results.
Changes observed when traffic data availability varies by region or road segment.
Expected Behavior
-----------------
Current traffic conditions influence route segments occurring in the present when RTT data is available.
Historical traffic data is used when RTT is unavailable.
Reference speeds are used as a final fallback when traffic information is not available.
ETA and isoline calculations may change over time as traffic conditions and data sources change.
Unexpected Behavior
-------------------
The following may warrant further investigation:
Significant ETA inconsistencies for identical requests submitted at the same time.
Missing traffic influence in regions where RTT coverage is expected.
Vehicle profile results that do not reflect configured routing options.
Products
--------
HERE Routing Services
HERE Isoline Services
Car Routing Profiles
* Truck Routing Profiles
Keywords / Tags
---------------
ETA, isoline, travel time, routing, real-time traffic, RTT, traffic patterns, free flow speed, speed calculation, truck routing, car routing, functional class, speed category, historical traffic, route estimation
Trucks
Updated 3 days ago