Traffic message channel
| Traffic message channel ： ウィキペディア英語版|
Traffic Message Channel (TMC) is a technology for delivering traffic and travel information to motor vehicle drivers. It is digitally coded using the ALERT C protocol into RDS Type 8A groups〔Dietmar Kopitz, Bev Marks. ''RDS: The Radio Data System.'' Artech House, 1999.〕 carried via conventional FM radio broadcasts. It can also be transmitted on Digital Audio Broadcasting or satellite radio. TMC allows silent delivery of dynamic information suitable for reproduction or display in the user's language without interrupting audio broadcast services. Both public and commercial services are operational in many countries. When data is integrated directly into a navigation system, traffic information can be used in the system's route calculation.
== Development ==
Detailed technical proposals for an RDS-TMC broadcasting protocol were first developed in the European Community's DRIVE programme〔Proposal for a Council Regulation (EEC) on a Community programme in the field of information technology and telecommunications applied to road transport - Drive (Dedicated road infrastructure for vehicle safety in Europe). COM(87) 351 final.〕 research project RDS-ALERT, a partnership of the BBC, Philips, Blaupunkt, TRRL and CCETT led by Castle Rock Consultants (CRC).〔Castle Rock Consultants. ''Radio Data System (RDS) Traffic Message Channel (TMC).'' Final Report to the Commission of the European Communities, DRIVE Project V1029, Nottingham, UK, October 1988.〕 The main goal of the project was to develop and build consensus upon a draft standard for broadcasting RDS-TMC traffic messages in densely coded digital form.〔S.R. Ely, BBC Research Department, Engineering Division, Kingswood Warren, Tadworth, UK. ''RDS-ALERT: a DRIVE project to develop a proposed standard for the Traffic Message Channel feature of the radio data system RDS'', IEE Colloquium on `The Car and its Environment - What DRIVE and PROMETHEUS Have to Offer (Digest No.20), 1990.〕
An initial proposal for defining RDS-TMC data fields had been made to the European Conference of Ministers of Transport (ECMT) in Madrid, based on a scheme developed by CCETT and Philips in the Eureka-sponsored CARMINAT research project.〔CARMINAT, Programme EUREKA (EU 55) : ''Realisation d'un systeme complet d' information, de gestion et de navigation a vocation Europeenne pour les vehicules routiers (EUREKA Programme (EU 55) : Development of a complete European information management and navigation system for road vehicles. )'' International Road and Traffic Conference. ''Roads and Traffic 2000.'' Vol. 1., p. 147-150. Text in French with summary in English. Coordinated by: Heusch/Boesefeldt G.m.b.H., Aachen Germany. Publication Date: 1988.〕 This proposal required the use of at least two 104-bit RDS data groups for each message. Within these RDS Groups, 32 bits per group would be used for traffic data, giving a total traffic message length of 64 bits. A second proposal, by Bosch-Blaupunkt and the German Road Research Institute BASt,〔Bundesanstalt für Straßenwesen. See German Wikipedia.〕 sought to use just a single RDS Group per traffic message. Then, in 1987, the CEC invited Castle Rock Consultants to lead a joint team that would take TMC development a stage further.〔J.L. Riley and A.K. McParland. ''RDS-ALERT: A proposed Traffic Message Channel (TMC) feature for the Radio Data System (RDS).'' BBC RD 1991/16, Research Department, Engineering Division, The British Broadcasting Corporation.〕 CRC produced a proposal for a modified BASt/Blaupunkt single group message definition, which became known as the ALERT A coding scheme. Tests also continued at CCETT and BBC on the CARMINAT approach, which formed the basis of an alternative ALERT B coding proposal.
A major question addressed in the Alert A scheme was the total number of traffic event locations to be coded. Initial estimates suggested that, in Europe, a maximum of 65,000 significant junctions might be needed for the Federal Republic of Germany. An efficient coding system would require only 16 bits to code these, simply by numbering each intersection from 1 to 65535. Calculations for France, Britain and elsewhere suggested that around 30,000 to 40,000 locations should be enough for most European national or U.S. statewide systems. A standard 16-bit location code was, therefore, adopted for inter-urban networks. The Madrid proposal of 1987, by comparison, had required 33 bits to code problem location, with separate fields for road number, road class, area of the country, etc. These 33 bits gave a theoretical total of 8.5 billion location codes, most of which could never be used.〔Peter Davies, Chris Hill, and Grant Klein. ''Standards for the Radio Data System - Traffic Message Channel.'' Castle Rock Consultants, Leesburg, Virginia, USA. Vehicles/Highway Automation: Technology and Policy Issues (SP·791). Future Transportation Technology Conference and Exposition, Vancouver, BC, Canada. August 7·10, 1989〕
After consultation with ECMT, a combined approach was developed called the ALERT C Protocol that aimed to combine the best features of each approach. ALERT A and C replaced the CARMINAT message categories cause, effect and advice by a single 11-bit basic message code. This permits up to 2048 basic message phrases to be broadcast. The new ALERT protocols significantly increased the efficiency of message coding, shortening the basic message content from 18 to 11 bits. In conjunction with the revised location codes, which saved 17 of the 33 bits previously assigned, this allowed the great majority of traffic messages to be broadcast using a single TMC data sequence. In 1991, ECMT recommended moving forward with further testing of the protocols.〔European Conference of Ministers Of Transport. Resolution No. 91/4 on Standards for Traffic Messages Broadcast using the Radio Data System Traffic Message Channel. ()〕 The work continued with a larger consortium including Volvo and Ford in the European Commission's DRIVE II project ATT-ALERT.〔Davies, P.; Milton, H. Castle Rock Consultants, Nottingham, UK. ''The development of integrated traveller information protocols.''Proceedings of the Intelligent Vehicles '94 Symposium, IEEE, 24-26 Oct. 1994, pages 602-605.〕
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