Location Referencing: TMC, Alert-C
By: Alessandro Attanasi
Tags: Alert C, Location Reference, Traffic, Rds Tmc, Maps

Location Referencing: TMC, Alert-C

The case of pre-coded locations and the need of radio broadcasting traffic information

Photo by Denys Nevozhai on Unsplash

In a prevoious post I introduced different ways in which geospatial information can be shared between different persons. Now I will focus on the case where we use pre-coded locations. Let’s remind that we are dealing with a situation where the actor A wants to communicate an information related to his map to anoter actor B having a different map. The strategy we are going to describe is to share a common predefined set of locations that each actor can relate to his map. In that way any data referred to such set can be transmitted between the two actors unambigously.

The most common used system of pre-coded locations is the RDS-TMC using Alert-C as defined by the standards ISO 14819–1:2013, ISO 14819–2:2013, ISO 14819–3:2013, ISO 14819–6:2006.

The ALERT-C protocol is designed to provide mostly event-orientated road end-user information messages. RDS-TMC messages are language-independent, and can be presented in the language of the user’s choice. The ALERT-C protocol utilises a standardised Event List of event messages with their code values, which also includes general traffic problems and weather situations. ALERT-C defines two categories of information within messages: basic and optional items. In principle, basic information is present in all messages. Optional information can be added to messages where necessary. Standard RDS-TMC user messages provide the following five basic items of explicit, broadcast information:

Event description, giving details of road event situation, general traffic problems and weather situations (e.g. congestion caused by accident) and where appropriate its severity (e.g. resulting queue length).

Location, indicating the area, road segment or point location where the source of the problem is situated.

Direction and Extent, identifying the adjacent segments or specific point locations also affected by the incident, and where appropriate the direction of traffic affected.

Duration, giving an indication of how long the problem is expected to last.

Diversion advice, showing whether or not end-users are recommended to find and follow an alternative route.

In addition to such basic information there are also optional ones, and among them we can find:

Road class and road number

Road segment

Area, region and country

Pre-assigned diversion advice

In the ISO 14819–1:2013 standard all these information are fully described and you can find exactly the binary content of the message bit per bit. While the ISO 14819–2:2013 standard defines the “Events List” to be used in coding the messages. Such list is composed by carefully selected English phrases for describing many type of events, and the corresponding translated phrases in other languages are officially available from the TMC Forum website. All listed events are identified by a numerical code to which correspond the phrase describing the event. The Event List also contains several predefined combinations of single phrase events and they are not always word for word identical to the corresponding phrases used in the single events. Binding words or small changes to the wording are necessary.

The basic messages are grouped in the following classes (with an example in brackets, and its code) :

Level of service (stationary traffic — 101)

(stationary traffic — 101) Expected level of service (queuing traffic expected — 114)

(queuing traffic expected — 114) Accidents (all accidents cleared, no problem to report — 141)

(all accidents cleared, no problem to report — 141) Incidents (rescue and recovery work in progress — 397)

(rescue and recovery work in progress — 397) Closure and lane restrictions (emergency lane closed — 637)

(emergency lane closed — 637) Carriageway restrictions (tunnel blocked — 27)

(tunnel blocked — 27) Exit restrictions (slip roads restrictions — 409)

(slip roads restrictions — 409) Entry restrictions (entry blocked — 473)

(entry blocked — 473) Traffic restrictions (smog alert — 1332)

(smog alert — 1332) Carpool information (police directing traffic via the carpool lane — 1963)

(police directing traffic via the carpool lane — 1963) Roadworks (new road layout — 811)

(new road layout — 811) Obstruction hazards (spillage on the road — 903)

(spillage on the road — 903) Dangerous situations (heards of animals on roadway — 1068)

(heards of animals on roadway — 1068) Road conditions (oil on road. Danger — 1057)

(oil on road. Danger — 1057) Temperatures (heavy frost — 1115)

(heavy frost — 1115) Precipitation and visibility (visibility reduced to < 50m — 1320)

(visibility reduced to < 50m — 1320) Wind and air quality (tornadoes — 1201)

(tornadoes — 1201) Activities (cricket match — 1457)

(cricket match — 1457) Security alerts (terrosit incident — 1478)

(terrosit incident — 1478) Delays (delays up to one hour — 1604)

(delays up to one hour — 1604) Cancellations (normal public transport services resumed — 1660)

(normal public transport services resumed — 1660) Travel time information (current trip time up to 25 minutes— 1695)

(current trip time up to 25 minutes— 1695) Dangerous vehicle (objects falling from moving vehicle — 1710)

(objects falling from moving vehicle — 1710) Exceptional loads/vehicles (convoy cleared — 1770)

(convoy cleared — 1770) Traffic equipment status (variable message signs operating — 1842)

(variable message signs operating — 1842) Size and weight limits (temporary width limit lifted — 1852)

(temporary width limit lifted — 1852) Parking restrictions (special parking restrictions in force — 1887)

(special parking restrictions in force — 1887) Parking (70% full — 1894)

(70% full — 1894) Reference to audio broadcasts (alarm set: new information will be broadcast between these times in normal programme — 1910)

(alarm set: new information will be broadcast between these times in normal programme — 1910) Service messages (rail information service resumed — 1965)

(rail information service resumed — 1965) Special messages (nothing to report — 2041)

One or more pieces of information can be appended to any message within the standard Event List, using codes contained within a list of supplementary information. They detail the message for what concerns:

Diversions, Vehicles

Warnings

Speeds

Instructions

Lane usage

Positions

Places

Reasons

Winter driving

Suggestions

Qualifiers

Directions

Courtesy

And forecast messages have their own status being coded separately and describing the following classes:

Level of service forecast

Weather forecast

Road conditions forecast

Environment

Wind forecast

Temperature forecast

Delay forecast

Cancellation forecast

While the standard ISO 14819–6:2006 describes how to properly encrypt the messages, the standard ISO 14819–3:2013 is entirely dedicated to the description of the locations.