diff --git a/gtfs/spec/en/reference.md b/gtfs/spec/en/reference.md
index 6bfd0884b..68a6b7fe1 100644
--- a/gtfs/spec/en/reference.md
+++ b/gtfs/spec/en/reference.md
@@ -174,6 +174,7 @@ File: **Required**
 |  bikes_allowed | Optional | 0 (or empty) - indicates that there is no bike information for the trip |
 |   |  | * **1** - indicates that the vehicle being used on this particular trip can accommodate at least one bicycle |
 |   |  | * **2** - indicates that no bicycles are allowed on this trip |
+|  vehicle_id | Optional | The **vehicle_id** field contains an ID that identifies a vehicle or set of vehicles on a trip.|
 
 #### Example showing blocks and service day
 
@@ -426,4 +427,4 @@ The file contains information about the feed itself, rather than the services th
 |  feed_lang | Required | The **feed_lang** field contains a IETF BCP 47 language code specifying the default language used for the text in this feed. This setting helps GTFS consumers choose capitalization rules and other language-specific settings for the feed. For an introduction to IETF BCP 47, please refer to http://www.rfc-editor.org/rfc/bcp/bcp47.txt and http://www.w3.org/International/articles/language-tags/. |
 |  feed_start_date | Optional | The feed provides complete and reliable schedule information for service in the period from the beginning of the **feed_start_date** day to the end of the **feed_end_date** day. Both days are given as dates in YYYYMMDD format as for [calendar.txt](#calendartxt), or left empty if unavailable. The **feed_end_date** date must not precede the **feed_start_date** date if both are given. Feed providers are encouraged to give schedule data outside this period to advise of likely future service, but feed consumers should treat it mindful of its non-authoritative status. If **feed_start_date** or **feed_end_date** extend beyond the active calendar dates defined in [calendar.txt](#calendartxt) and [calendar_dates.txt](#calendar_datestxt), the feed is making an explicit assertion that there is no service for dates within the **feed_start_date** or **feed_end_date** range but not included in the active calendar dates. |
 |  feed_end_date | Optional | (see above) |
-|  feed_version | Optional | The feed publisher can specify a string here that indicates the current version of their GTFS feed. GTFS-consuming applications can display this value to help feed publishers determine whether the latest version of their feed has been incorporated. |
\ No newline at end of file
+|  feed_version | Optional | The feed publisher can specify a string here that indicates the current version of their GTFS feed. GTFS-consuming applications can display this value to help feed publishers determine whether the latest version of their feed has been incorporated. |