Road Weather Data

The Road Weather data API provides real-time calculated driving condition forecasts to any coordinate point in the world. The state of the road’s surface, visibility and other weather events affecting driving are included. Over 40 varieties of driving condition codes are divided into green, yellow and red road segments, representing the severity class.

Vaisala's experts have developed competence in road weather forecasting for many years. These forecasts are trusted in the winter maintenance industry by road authorities in a number of countries. Now, the data is available for other industries as well. The Road Weather data API provides information designed to be from the drivers perspective and as a result is now also being used for autonomous driving purposes.

The Road Weather data API has the capability to provide real-time calculated driving condition forecasts to any coordinate point in the world. The API gives you driving condition information about the state of the road surface, visibility and atmospheric weather events affecting driving. You are able to track both current conditions and forecasts for the roads.

Three Severity Levels

Vaisala offers 40+ variations of codes to express driving conditions. The road condition code is delivered as an integer value, which is mapped into human-readable names in a given language. The codes are divided in three types of classes to express the severity level. The severity level can be tailored to take into account seasonal changes and driving specifics such as an assumed general use of winter tyres. Below is an example of road condition codes used in three severity levels. Please contact us for the complete list of codes.

Normal Conditions

  • Dry road
  • Moist road
  • Wet road
  • Light/moderate rain
  • (some slush/snow when winter tires assumed)

Risky Conditions

  • Heavy rain
  • Strong winds
  • Patches of fog
  • Risk of aquaplaning

Hazardous Conditions

  • Very strong winds
  • Risk of damaging hail
  • Poor visibility due to: very heavy rain, dense fog, blowing snow,  blizzard
  • Slippery due to: snow, icy road,  water on icy road,  slush on road, freezing rain

Delivery Options


Driving condition information for the current coordinates of a vehicle, or on a route that consists of several coordinates and projected timestamps, can be queried in XML or JSON formats. The type of road (primary road, secondary road, or bridge) can be provided for a better estimation of the road condition.

Gridded data

Customers that would like to map the road condition information into road segments themselves, can have the forecast data delivered as longitude-latitude grids. These grids are similar to images where each pixel would represent a constant-size square in WGS-84 degrees. Since there can be multiple roads inside the same pixel, nearby roads of different types are covered by providing multiple grids, one per road type (primary road, secondary road, bridge).

Road segments

Driving conditions data can be delivered in batches of pre-set locations that are updated regularly, usually once per hour. This removes the need to map the data into road segments. Often the simplest way to use the service is to have atmospheric forecasts for points of interest (such as cities) displayed in an infotainment system, separate from the road condition forecast.




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Key Benefits

Driving Condition Codes
All weather phenomena that affect driving conditions are simplified into one variable, which we call the road condition code. Road surface condition (dry, wet, icy, …), precipitation amount and type, visibility and many other parameters are considered. A road condition code is chosen to represent the most significant phenomenon that is measured or forecasted to be present. Road weather forecasts are based on the combination of Vaisala´s atmospheric weather model and road weather model. In addition, the effect of possible road maintenance actions, like plowing and salting the roads by national road authorities, are taken into consideration to provide a comprehensive view of the road conditions. The predicted maintenance actions are based on the assumption that the treating has been executed according to the common winter maintenance policies. Please note that similar conditions can lead to different codes in different regions. For example, in countries where using winter tires is mandatory, small amounts of snow or frost are considered less severe than elsewhere.
Resolution and coverage
Most of the content in the service depends on local data sources, which causes the resolution and the set of parameters to vary per region. Atmospheric weather forecasts and satellite data are available globally and resolution varies between 1 km and 10 km. Additionally radar data is available in selected markets. Road condition forecasts are currently available for most of Europe, but new regions and countries can be added upon request. Resolution varies between 2 km and 10 km, depending on the region. Resolution of any area can be improved upon request. All the key factors affecting local road conditions (see illustration) are analysed and taken into consideration in road weather forecasts. However, maintenance activities and traffic information are used only where data is available.
Vehicle Sensor Data
It is possible to integrate sensor data from vehicles into the Road Weather service. Connected vehicle sensor data could be effectively utilized as an additional data source for improving road weather forecasts. Typically, cars are a good source for detecting local precipitation events and the presence of water on the road. Additionally, cars can provide temperature information, especially in areas where road weather stations are scarce or their data is not available. Currently, there is no third-party car sensor data that would be available for all customers, but Vaisala is capable of aggregating and utilizing customer-specific data sources.