How announcements are ordered in Google Maps

The values of an alert’s effect, cause and informed_entity help determine the order in which the alerts are displayed when multiple alerts are applied on the same trip and/or stop on different surfaces.

To understand the order of alerts, refer to the following as an example:

id: "1"
alert {
  informed_entity {
    agency_id: "state_railway"
  }
  cause: MEDICAL_EMERGENCY
  effect: OTHER_EFFECT
  url {
    translation {
      text: "https://staterailway.info"
      language: "en"
    }
  }
  header_text {
    translation {
      text: "Changes in service capacity"
      language: "en"
    }
  }
  description_text {
    translation {
      text: "Until further notice, this service will be operating at half capacity"
      language: "en"
    }
  }
  uid: 11490810685792836703
}

id: "2"
alert {
  informed_entity {
    route_id: "G4"
  }

 active_period {
    start: 1590933600
    end: 1598796000
  }
  effect: DETOUR
  cause: OTHER_CAUSE
  header_text {
    header_text {
    translation {
      text: "Detour at Middle Street"
      language: "en"
    }
  }
  description_text {
    translation {
      text: "Route G4 will not run past Middle street due to road works but will run a temporary alternative stop along 1st Street"
      language: "en"
    }
  }
}
id: "3"
alert {
  informed_entity {
    route_id: "C5"
  }
  effect: OTHER_EFFECT
  cause: OTHER_CAUSE
  header_text {
    translation {
      text: "Bike permitted with fees"
      language: "en"
    }
  }
  description_text {
    translation {
      text: "Bicycles are permitted on this service, although additional fees may apply. Please check that the operator has space prior to travelling."
      language: "en"
    }
  }
}

Search results page

In the routing results page, the trip will be marked with an icon based on the highest alert category:

• Critical 
• Warning 
• Informational 

For example, the DETOUR effect has the highest categorization of alert warning, so  is used.

Trip details page / Departure board

When multiple alerts are used on a particular trip or stop, they’ll be ordered by impact score. An alert’s impact score is calculated with the values in the effect, cause, and informed_entity fields.

Impact scoring for effect

For the effect field, the impact score is given based on the severity of the disruption. The values and impact score are ordered as follows in descending order:

• NO_SERVICE
• REDUCED_SERVICE
• SIGNIFICANT_DELAYS
• DETOUR / ADDITIONAL_SERVICE / MODIFIED_SERVICE / STOP_MOVED / OTHER_EFFECT when used in conjunction with MEDICAL_EMERGENCY as Alert cause
• OTHER_EFFECT / UNKNOWN_EFFECT

Impact scoring for cause

For the cause field, only MEDICAL_EMERGENCY is given a high impact score, while the rest are of equal impact.

Impact scoring for informed_entity

For an informed_entity, the impact score is given with respect to the extent of the network that is affected. If multiple informed_entity entries are given for the same alert, only the most restrictive range is considered.

The different combinations of informed_entity and its impact score are ordered as follows in descending order:

• Agency wide 
• Route or route passing through at specific stop
• Trip or trip passing through at a specific stop
• Stop or agency wide trip at a particular stop

Learn more about how to select entities.

Following table shows the higher impact score (bolded) in the above example.

Alert ID	Cause impact	Effect impact	Entity impact
1	MEDICAL_EMERGENCY	OTHER_EFFECT	Agency wide
2	OTHER_CAUSE	DETOUR	Route
3	OTHER_CAUSE	OTHER_EFFECT	Route

Thus, the first alert to appear is the alert with id 1 as it has a higher impact score across the cause and informed_entity fields as compared to the other alerts.