Add new optional field SeverityLevel to Service Alerts feed

gtfs-realtime/proto/gtfs-realtime.proto

@@ -435,6 +435,17 @@ message Alert {
   // Text for full description for the alert to be used in text-to-speech implementations. This field is the text-to-speech version of description_text.
   // This field is still experimental, and subject to change. It may be formally adopted in the future.
   optional TranslatedString tts_description_text = 13;
+
+  // Severity of this alert. 
+  // This field is still experimental, and subject to change. It may be formally adopted in the future.
+  enum SeverityLevel {
+	UNKNOWN_SEVERITY = 1;
+	INFO = 2;
+	WARNING = 3;
+	SEVERE = 4;
+  }
+
+  optional SeverityLevel severity_level = 14 [default = UNKNOWN_SEVERITY];
 
   // The extensions namespace allows 3rd-party developers to extend the
   // GTFS Realtime Specification in order to add and evaluate new features

gtfs-realtime/spec/en/reference.md

@@ -66,6 +66,7 @@ Fields labeled as **experimental** are subject to change and not yet formally ad
             *   [Effect](#enum-effect)
             *   [TranslatedString](#message-translatedstring)
                 *   [Translation](#message-translation)
+            *   [SeverityLevel](#enum-severitylevel)
 
 # Elements
 
@@ -267,6 +268,7 @@ An alert, indicating some sort of incident in the public transit network.
 | **description_text** | [TranslatedString](#message-translatedstring) | Required | One | Description for the alert. This plain-text string will be formatted as the body of the alert (or shown on an explicit "expand" request by the user). The information in the description should add to the information of the header. |
 | **tts_header_text** | [TranslatedString](#message-translatedstring) | Optional | One | Text containing the alert's header to be used for text-to-speech implementations. This field is the text-to-speech version of header_text. It should contain the same information as header_text but formatted such that it can read as text-to-speech (for example, abbreviations removed, numbers spelled out, etc.) **Caution:** this field is still **experimental**, and subject to change. It may be formally adopted in the future. |
 | **tts_description_text** | [TranslatedString](#message-translatedstring) | Optional | One | Text containing a description for the alert to be used for text-to-speech implementations. This field is the text-to-speech version of description_text. It should contain the same information as description_text but formatted such that it can be read as text-to-speech (for example, abbreviations removed, numbers spelled out, etc.) **Caution:** this field is still **experimental**, and subject to change. It may be formally adopted in the future. |
+| **severity_level** | [SeverityLevel](#enum-severitylevel) | Optional | One | Severity of the alert.<br>**Caution:** this field is still **experimental**, and subject to change. It may be formally adopted in the future. |
 
 ## _enum_ Cause
 
@@ -307,6 +309,20 @@ The effect of this problem on the affected entity.
 | **UNKNOWN_EFFECT** |
 | **STOP_MOVED** |
 
+## _enum_ SeverityLevel
+
+The severity of the alert.
+
+**Caution:** this field is still **experimental**, and subject to change. It may be formally adopted in the future.
+
+#### Values
+| _**Value**_ |
+|-------------|
+| **UNKNOWN_SEVERITY** |
+| **INFO** |
+| **WARNING** |
+| **SEVERE** |
+
 ## _message_ TimeRange
 
 A time interval. The interval is considered active at time `t` if `t` is greater than or equal to the start time and less than the end time.