‫ە‬Messages from Departments and Centers of NILIMOn the subject of probe data
FUJIMOTO Satoshi,
Director of the Research Center for Advanced Information Technology(Key words) Probe, probe data, ITS spots
1. Introduction
Recently, we often hear talk of “probes”. The
dictionary definition of a “probe” is “a slender, flexible
surgical instrument used to explore a wound or bodycavity”, or “a vehicle equipped to obtain scientificinformation (space probe) ” (extracts from Collins
English Dictionary). In the field of electronic devices,
meanwhile, a probe can also be a lead connecting to or
containing a measuring or monitoring circuit used fortesting.
In the field of road traffic, a traveling vehicle fittedwith sensors is called a “probe car”, and the datacollected by those sensors are called “probe data”.
Moves are afoot to take these data and subject them toprocessing and analysis, making them available forbroad use in services in the road traffic sector.
2. What is a probe?
While the term “probe” is still somewhat unfamiliarin the field of civil engineering, it has long been incommon use in other fields. To quote a recent case, forexample, when the unmanned spacecraft Hayabusa
returned to earth with microparticles from the asteroid
Itokawa, the BBC reported the news with the headline“Japan probe collected particles from Itokawa asteroid”.
It is also used with frequency in a social or politicalsense, and is often seen in English-language news (forexample, in connection with ‘spy probes’ orinvestigations of contagious diseases).
In the road traffic sector, the use of probe data was
first considered in the second half of the 1990s. In 1999,for example, the Japan Automobile Research Institute(JARI) led an initiative for a “Feasibility study on thedevelopment of an ITS probe car system”, while ataround the same time the Ministry of Land,
Infrastructure, Transport and Tourism started studying
the use of probe cars in highway administration. An
example of this was a study on the creation of a probe
car system by the Chugoku Regional Development
Bureau. Monitoring devices fitted with functions for
obtaining positional and other data using GPS (globalpositioning systems) and functions for communication
were attached to vehicles constantly in use, such as
official vehicles and buses. Existing communication
networks were then used to gather positional data fromeach vehicle with the passage of time.
3. Probe data
Probe data that can be obtained from a motor vehicle

include data obtainable from navigation systems, suchas the time and position (longitude and latitude), i.e.
data on the vehicle’s running history, and front-rearacceleration or right-left acceleration, i.e. data on thevehicle’s performance history. Since these probe data
can be obtained continuously over time from eachsingle vehicle, if a system could be constructed
whereby data could be acquired from a considerable
number of vehicles, it would allow us to monitor thestate of road traffic at any chosen location or point intime.
Probe data on the running history mentioned above isobtained by aggregating compound technologies
consisting of GPS technology, map matching
technology, and digital road maps. Of these, positional
measurement by GPS can take two forms, namely
single point measurement and relative positional
measurement, the former of which is used for car
navigation systems. With this method, the position of
one’s own vehicle and the time of that position areobtained by calculating the longitude, latitude,elevation and time (i.e. the time on a nuclear clock
mounted on GPS satellites) by receiving transmission
signal data from four GPS satellites. The data received
here, however, are inconsistent in their precision,owing to ionospheric delay in the radiowave
propagation pathway, the state of the earth’s
atmosphere, and other factors. GPS receivers incommon use are set to a standard allowing them toreceive positional identification to within 10 metersfrom the correct longitude and latitude to a probabilityof 95%. In future, this inconsistency is expected to be
vastly improved through the use of quasi-zenithsatellites. However, it will probably be some time
before quasi-zenith satellites are operating 24 hours a
day over Japan; only one (“Michibiki”) is in orbit at themoment, and two more are still needed.
Map matching technology is a corrective method
whereby, since cars basically only drive on roads, thelongitude and latitude obtained by GPS positional
measurement are plotted on the links on a digital road
map. While this method has been used by various
navigation system manufacturers to improve precisionusing their own technology, there are somecomplications with patents. As a result, eachmanufacturer uses a different specific techniqueproducing a different level of precision, and the method
is not yet in the public domain.
As shown above, probe data on a vehicle’s running‫ە‬Messages from Departments and Centers of NILIM

history obtained from car navigation systems currently
present some problems over the inconsistency ofprecision when in use.
4. Verification of probe data
With a view to starting a nationwide service using
ITS spots between January and March 2011, theMinistry of Land, Infrastructure, Transport andTourism has installed about 1,600 ITS spots, mainly on
expressways all over the country, in a public-private
collaboration. The spot communication used in these
ITS spot services has the characteristic of facilitatinglarge-volume communication in both directions.
Car navigation systems compatible with ITS spots
are fitted with GPS receivers, acceleration sensors,
gyrosensors and other devices, allowing them to obtainand accumulate the vehicle’s running history data andperformance history data. The probe data accumulated
here are up-linked every time the vehicle passes an ITS
spot, and are also aggregated in the probe server. The
data thus gathered are called “road probe data”, todistinguish them from other probe data.
The use of road probe data is being considered in avariety of situations, but for the time being, the aim is toprocess them into average traveling time and average
traveling speed per unit of links on digital road maps.
This will make it possible to capture the daily changing
state of road traffic at any time.  However, while a variety of devices are beingdeveloped and gradually starting to be used to gather

road probe data, before that, as stated in the previous
section, I think the gathered data will need to beverified. Specifically, this system has been given
parameters that can be set as appropriate by theadministrator (for example, when calculating average
traveling time and producing data on a given vehicle
traveling significantly faster or slower than the average,
the threshold value for removing or retaining thosedata). Nevertheless, I think it will be necessary to tune
these to appropriate values, having verified therelevance of these parameter values using actual data.
Also, it will be essential to verify whether or not thedata are being processed in the sequence specified in
the equipment specifications, or whether or not the data
are being uplinked in accordance with the format ofroad probe data determined in advance.
5. Conclusion
 In this modern age of advanced car electronics,
many other types of data exist as probe data related to
motor vehicles, besides those mentioned here. One
direction for research in the ITS field in future could beto study how effective use can be made of these probe
data, but verifying the data themselves will be
indispensable as a prerequisite to that.
Reference
Traffic Engineering2003 No.4 Vol.38Japan Societyof Traffic Engineers