Intelligent Roadway Information System


High-occupancy / toll (HOT) lanes can be operated through IRIS. Functions include logging vehicle transponder (tag) information, calculating tolls in real time, and displaying prices on DMS.

Customer accounts and billing are not supported; those features must be provided by an external system.

Tag Readers

Select View ➔ Lane Use ➔ Tag Readers menu item

A tag reader is a sensor for in-vehicle transponders (tags). They can be mounted over a tolled lane to record customer trips. These are typically located just downstream of a pricing DMS.

API Resources 🕵️
  • iris/api/tag_reader (primary)
  • iris/api/tag_reader/{name}
Access Primary Secondary
👁️ View name, location geo_loc, settings
💡 Manage notes toll_zone
🔧 Configure controller pin

Tag Read Events

When a tag is read, an event is logged in the tag_read_event database table. The event includes the date and time, tag ID, toll zone and tollway. This can be combined with the price message events to build a list of trips for each tag ID. This information can be used to bill customers.

These records are purged automatically when older than the value of the tag_read_event_purge_days system attribute.

Toll Zones

Select View ➔ Lane Use ➔ Toll Zones menu item

A toll zone is a segment of roadway between two stations. All HOT lane detectors between the starting station and ending station can be used to calculate the toll. Every 3 minutes, tolls are calculated using data from the most recent 6 minutes. Within a zone, each station has an associated toll, based on the highest density k recorded among HOT lane detectors downstream of that station.

p = α ⋅ k β

The toll price is then rounded to the nearest $0.25.

Pricing on DMS

The toll price can be displayed in DMS messages using DMS actions. A [tz ] action tag in the message pattern will be replaced with the appropriate value. It has the following format:

[tz mode,{tz0},…{tzn} ]


  1. mode: Tolling mode:
    • p: priced
    • o: open
    • c: closed
  2. tz0: First toll zone ID
  3. tz1 - tzn: (Optional) additional toll zone IDs

If the tolling mode is priced, the tag will be replaced with the calculated price, for example 2.75. It will be the sum of prices for all specified toll zones. The values of the toll_min_price and toll_max_price system attributes limit the calculated price.

For open and closed modes, the tag will be replaced with an empty string. If required, a message such as OPEN or CLOSED may be appended after the tag.

Price Message Events

Price events are logged when a message is sent to a DMS, and again when the message is verified. The price event includes the date and time, DEPLOYED or VERIFIED status, DMS id, toll zone, highest density detector(s) and price.

The logged toll zone is the last zone specified in the tag. In priced mode, the displayed price is logged. For open or closed, a price of 0 is logged.

These records are purged automatically when older than the value of the price_message_event_purge_days system attribute.