The Development of Free-Flow
ETC System and the Future

TAKESHI HANABATAYOSHIFUMI HAYAKAWASHIGEHIRO HISHIKAWA
MASANORI TANAKAThe newly developed free-flow electronic toll collection (ETC) system is a toll collection system aimed at solving
such problems of city expressways as: (1) easing of traffic congestion at the center of the city, (2) improvement ofenvironment along the expressways, (3) procurement of land (site) for new toll plaza and (4) diversification of toll
system. The system has started joint operation as an ETC system for transit vehicles at Hanshin Expressway Public
Corporation since July 2002, and is expected to be used successively as an ETC system for special zone toll collection
by the end of fiscal year 2002, and as the ETC system for transit vehicles via ETC of Kobe Municipal Expressways
Public Corporation. The system easily applicable to the road pricing system can be used as an unmanned system not
only in city expressways, but also in other public corporations for roads and expressways.
from slowing down or making a stop as he or she approaches
the existing toll plaza using the conventional ETC system,and enables to read or write the passage data (passage history, utility details, etc.) through communication between
the onboard unit (equipment) and the road side equipment
as the vehicle passes under the gantry.

1. Introduction
The free-flow ETC system is a system of collecting tolls
without requiring the passing vehicles to stop at the tollcollecting plazas. The system is similar to the electronic roadpricing (ERP) system operating in Singapore since 1998.
The new free-flow ETC system has been developed for
Hanshin Expressway Public Corporation as an ETC system for transit vehicles. The ETC transit is a system thattreats the unlinked different roads as if they were a continuous road, allowing only the ETC vehicles passing throughthe specified transit zone during specified time to pass.
The Hanshin Expressway Public Corporation has been
adopting a manned system of exempting toll collection fromvehicles running through the designated transit routes byrequiring the driver to take the transit ticket at the transit exit gate and to submit it at the transit entrance gate.
In July 2002 the ETC system was introduced in all entrance toll plazas and the free-flow ETC system wasinstalled at 4 transit exit gates between Kobe Route No. 3
and Wangan (Gulf) Route No. 5 (Kyobashi, Maya, Rokko
Island Kita and Sumiyoshihama). Fig. 1 shows the schematic diagram of the route. Unlike the ETC systeminstalled at toll plazas (hereafter "conventional ETC system"), the new system has been developed for toll plazaswith no reserve (median) called island for each lane or forthe lane where the installation of the conventional ETC
system is difficult.

3. Urban expressway system and future problems
Below is the brief description how the newly developed
free-flow ETC system deals with the problems of urban
expressway given below.
(1) Easing of traffic congestion at the center of the city(2) improvement of environment along the expressways(3) procurement of land (site) for new toll plaza(4) Diversification of toll system
Compared with the conventional ETC system, the freeflow ETC system has been developed for vehicles runningfreely at high speed. However, the traffic congestion evenin the same lane of an urban (city) expressway depends
also on the day and time zone. Widening the lane and increasing the number of toll plazas are suggested as thesolution to such problems, but the flow of traffic volume canbe dispersed by introducing the road pricing system, etc.
In order to restrict the number of cars (traffic volume)
passing through residential areas, environmental road pricing is already carried out in some routes (between Kobe
Route No. 3 and Wangan Route No. 5) of Hanshin Expressway Public Corporation. In order to adjust the traffic
volume strictly, however, appropriate installation (introduction) of the free-flow ETC system is effective, as thesystem can be applied not only to the transit to the otherroutes, but also to the diversified toll systems such as roadpricing (passage discount, time-wise discount, etc.) and tollcollection at special zones.

2. Outline of free-flow ETC system
The free-flow ETC system, differing largely from theconventional ETC system in equipment configuration, is
composed of the portal gantry (hereafter "gantry") installedon the off ramp or over the main lane. This exempts driver

Mitsubishi Heavy Industries, Ltd.
Technical Review Vol.40 No.3 (Jun. 2003)

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Chugoku Motorways,
Japan Highway Public Corporation

Nishinomiya Yamaguchi Jct.

Nishinomiya Yamaguchi Jct./Nishinomiya
Yamaguchi Higashi
Nishinomiya Yamaguchi
Minami Special Zone RouteNishinomiya Yamaguchi Higashi
Minotani

Nishinomiya Yamaguchi Minami
Kita Kobe Route No.7
Kobe Municipal Road Corporation (Minotani Toll Plaza)

Kobe
NagataTransit route between Kita Kobe Route No.7
and Kobe Route No.3

Shin Kobe Tunnel toll road
Yanagihara

IkutagawaTransit route between Kita Kobe Route No.7
and Kobe Route No.3

Kobe Route No.3
KyobashiMaya
Transit route between Kita Kobe Route No.3
and Wangan Route No.5

Free-flow ETC system

Sumiyoshihama: Operation started in July 2002
Wangan Route No.5

: Currently under construction
Rokko Island Kita
Fig. 1 Route schematic diagram
CenterLocal communication station

GantryRoadside
antenna 1

CentercomputersystemLanecontroller

Roadside
antenna 2: Signal line
: Power line

Roadside
relay unit
Imaging unit 1
Local substation
Power supply

Uninterruptible
power equipment

Imaging unit 2

Fig. 2 System configuration

3.1 Points of difference between free-flow ETC systemand conventional ETC system
As mentioned above, the newly developed systems are
installed in all 4 exits on two-lane off ramps. This allows
the vehicles to run freely on different lanes (cruising lane/
overtaking lane), needing a system different from the conventional ETC system where vehicles entering each lane
are subjected one by one to sequential transaction.
3.2 Features of urban expressway system
The peripheral roads run adjacent to one another or
are under the elevated roads as the special features of
the urban expressways. This, however, should not obstruct
the communication due to the leakage of radio waves outside the roads, and calls for a communication systemcapable of distinguishing without fail the vehicles running in parallel/diagonal or running fast/slow (as in traffic
congestion).
Unlike the conventional ETC system where the system
can be brought to stop for maintenance or due to sometrouble simply by closing the concerned lane only, the freeflow ETC system lanes cover the full width of the off ramp,

so that "closing of lanes" = "closing the traffic." Therefore,a double system has to be adopted, so that when one system is out of use for maintenance or due to some trouble,
the other system can be operated.
Further, the system must have a remote monitoring
system installed to the center computer system to monitor
the operating status of the system and to carry out remotecontrol (for start and stop of operation) to allow round-theclock unmanned operation.
In order to solve the aforesaid problems, the following
items were taken as the system requirements at the timeof development.

4. System specifications
The system configuration of the newly developed system is shown in Fig. 22, with the camera unit being an
optional function.
4.1 System requirements(1) Non-stop round-the-clock unmanned operation and remote operation (start and stop) from center computer
system must be possible.
Mitsubishi Heavy Industries, Ltd.
Technical Review Vol.40 No.3 (Jun. 2003)2

(2) All roadside equipment can be installed on the gantry.
(3) The system must be capable of simultaneous radio communication with multiple vehicles running freely along
the full width of the road. Further, the system must beable to recognize the license plate number as an optional
function.
(4) The radio frequency (RF) communication must be 2antenna type to enable communication over the roadwidth ranging from 5.5 m (single lane + shoulder zone)
to 7.0 m (2 lanes). Further, the radio frequency communication unit must cover the communication of 2 lanes
using one antenna in case the other one gets out of order.
(5) The roadside antenna must suppress the radio wave
from leaking out of the road, preferably needing no wall
for radio wave absorption.
(6) The lane controller must be installed more than several kilometers away from the roadside equipment.
(7) The lane controller must be able to continue operation
using the roadside system even if some circuit trouble(error) occurs in the center computer system. It must
be capable of storing the detailed utility data to transmit automatically to the center computer system after
the circuit returns to normal state.
4.2 System specifications(1) The roadside RF unit will have the roadside antennaconstantly activated.
(2) The communication slot will be of full-duplex 4-slot configuration.
(3) The roadside antenna will be installed as per roadside
RF unit, with the 2-antenna, frequency-division multiple-access control adopted for RF communication.
The communication range will cover 4.5 m in the moving direction of the vehicle, with the leakage of radio
wave out of the lane preferably suppressed.
(4) The lane controller will have the control units (transmission control unit, roadside RF unit) designed to have

independent power ON/OFF function so as to allow theoperation to continue even if the control unit gets partly
out of order. In addition, the lane controller will havethe backup memory.
(5) The license plate number recognizing unit as an optional function will recognize the license number plate
data (size, color, RIKUSHI <area> code, vehicle-typecode, usage code and sequence number) from the frontof the vehicle photographed by the camera before transmitting the data together with the image data to thecenter computer system.
4.3 Specifications for transit
In the case of Hanshin Expressway Public Corporation,
vehicles enter the area specified as transit zone by passing
through the general roads.
Vehicles not using ETC system use the transit system
by getting a transit ticket at the transit exit gate and submitting the ticket at the transit entrance gate, needing nocollection of passage toll.
In the case of vehicles using ETC system, however, they
get charged with the normal toll when they pass throughthe transit entrance gate.
Further, if the driver of a vehicle using ETC submits
the transit ticket, he or she must have the collected toll
paid back, making the passage of vehicles all the more complicated.
Hence it is necessary to record the transit exit data in
the IC card mounted on the onboard equipment at the transit exit gate, and to read the data at the transit entrance
gate to carry out automatic processing of transit.
(1) Processing at transit exit gate
The outline of ETC transit system is shown in Fig. 33.
(a) The lane controller receives the "transit exit table"from the center computer system.
(b) The roadside RF unit reads the "onboard equipment
and IC card data" from the onboard equipment andCenter computer system

Detailed ETC utilization data
ETC service data

Transit exit table

License Plate number recognition data
Image data

Detailed ETC
utilization data
ETC service data

Conventional ETC system(Transit entrance)

Free-flow ETC system (transit exit)
Optical fiber
Read data
Roadside
relay unit
(onboard equipment
Roadsideand IC card data)antennaTransitentrance table

Read data(Onboard equipment andIC card data/Transit exit data)

Lane
controller
Local communication station

Write data
(Detailed utility data)

Imaging unit
(camera)Roadside antenna

Write data
(Transit exit data)
Vehicle presence detector 1 Vehicle presence detector 2 Lane controller
Fig. 3 Outline of ETC transit system

Mitsubishi Heavy Industries, Ltd.
Technical Review Vol.40 No.3 (Jun. 2003)3

IC card.
(c) The roadside RF unit checks the validity of theonboard equipment and IC card.
(d) If found normal through the check, the "transit exit
data" is written on the onboard equipment and IC
card through RF communication.
(e) The transmission control unit prepares the detailed
utility data and calculates the total number of passing vehicles through the result of the recognition
made by the license plate number recognizing unit
before transmitting the data to the center computer
system. These data are also stored in the backup
memory.
(f) The license plate number recognizing unit as an optional function transmits the license number plate
recognition data of the passing vehicles together with
the image data to the center computer system wheninquiry or confirmation is made by the user.
(2) Processing at the transit entrance gate(a) The lane controller receives the "transit entrance
table" from the center computer system.
(b) The roadside RF unit activates the roadside antennausing the vehicle entrance signal to read the "onboard
equipment and IC card data" and "transit exit data"from the onboard equipment and IC card.
(c) The roadside RF unit checks the validity of theonboard equipment and IC card.
(d) If found normal through the check, the "detailed utility data" is written on the onboard equipment andIC card of the transit vehicle using the RF communication.
(e) The transmission unit prepares the detailed utility
data to transmit to the center computer system.

multiplexing type), and (IV) 3-antenna system (transmit/receive antenna separation type). The outline of the1.
aforesaid systems (I)-(IV) is given in Table 1(3) Laboratory test result
Tests including function of the onboard equipment
were carried out to confirm the optimum system out of
the aforesaid systems (I)-(IV), with the outline of the2.
laboratory test given in Table 2(4) Evaluation and study of communication system
It has been confirmed through laboratory tests thatthe aforesaid (I)-(III) systems could be applied. Of thesesystems, we came to conclusion that the double-antenna,frequency-division multiplexing system was optimum
system from the standpoints of cost, maintainability andreliability.
Fig. 4 shows the view of field test, while Fig. 5 theLeft antenna

Right antenna

Lane for communication

Fig. 4 View of field test
Example of communication zone measurement of free-flow ETC systemantenna carried out at Futami Plant test course of Mitsubishi Heavy
Industries, Ltd.

5. Features and achievements of the technology
5.1 Radio frequency (RF) communication technology(1) Antenna design concept
In designing the antenna for free-flow ETC system(status quo, 2-lane) the following items were given substantial consideration.
(a) Ensuring high-reliability communication: Formationof communication range of lane width 6.6 m x length
4.5 m(b) Reduction of garbage communication: Minimizationof radio wave leakage to the adjacent lane
In order to satisfy the aforesaid two requirements
there are two systems: the single antenna system thatcovers two lanes using one antenna by widening the antenna beam pattern and the multi-antenna system thatcovers multiple lanes using multiple antennas.
(2) Selection of communication system
The communication systems applicable to the freeflow ETC system are: (I) single antenna system, (II)double antenna system (frequency division multiplexing type), (III) double antenna system (time-division

5: Actually measured valueof communication zone
: Simulated value

Communicationzone

4

In width direction (m)32Vehicleforwarding
direction
Left antenna

10Vehicle-1 forwarding
direction-2

Right antenna-3-4

6.6 m X 4.5 m zone

-5
-10 -9

-8

-7

-6

-5

-4

-3

-2

-1

0

1

2

In the forwarding direction (m)Fig. 5 Results of simulation of double antenna combined communication zone and actual measurement
Comparison between the simulated communication zone of the freeflow ETC system antenna and actually measured value(onboard equipment height: 1 m)

Mitsubishi Heavy Industries, Ltd.
Technical Review Vol.40 No.3 (Jun. 2003)

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Table 1 Outline of communication method
Explanatory drawing

System name

OutlineSingle-antenna
system

A system that covers the communication zone
equivalent to 2 lanes using one (single) antenna.
It is necessary to change the number of elementsof the current ETC antenna and to study the
optimization of communication zone. However,
the expansion of communication zone involves a
problem of how to reduce the radio wave leakage
to the neighboring lanes.

Frequencydivisionmultiplexing(FDM) typeDoubleantenna
systemTimedivisionmultiplexing(TDM) typeA system that can be applied, with the current ETC
antenna left intact. Communication is made with thevehicles running on two lanes by using two
antennas with different frequencies. There is noneed of optimization of communication zone sinceeach lane is covered by a different antenna, butneeds verification about the interference from theneighboring channel.

A system that applies the current ETC antenna as
it is, with the communication made using two
antennas with the same frequency by switching thetiming for transmitting/receiving the signal. As
shown in the figure, it is necessary to carry out
verification that there is no radio interference fromthe neighboring antenna or onboard equipment.

Roadside antenna

Roadside antenna
communication zone

Lane 1 Lane 2
Vehicle forwarding direction

Frequency f1,
Roadside antenna 1
Roadside antenna 1
communication zone

Frequency f2,
Roadside antenna 2

Lane 1 Lane 2

Vehicle forwarding direction
Roadside antenna 1 Roadside antenna 2(Receive)(Transmit)

Transmit/
receive
Tripleantenna antenna
system separation
type

Roadside receive antenna 1

Uplink communication zone 1

Roadside antenna(Receive)

Onboard equipment 1 Onboard equipment 2(Receive)(Transmit)
Downlink interference

Onboard equipment
Uplink interference

As shown in the figure, this system separates thetransmit antenna from the receive antenna, with theone transmit antenna covering the downlink area ofmultiple lanes, while the receive antennas installed
one on each lane covering the uplink area. Thissystem has an advantage that the overall communication zone can be limited by reducing the uplinkarea.

Roadside antenna 2
communication zone

Lane 1

Roadside transmit antenna
Lane 2 Roadside receive antenna 2

Vehicle forwarding direction
Uplink communication zone 2
Downlink communication zone

Table 2 Results of evaluation of each system
System name

Test results

Single-antenna system

Communication zone: Communication zone of width 6.6 m X length 4.5 m or over is available.
Radio wave leakage: Although designed to minimize the leakage, the radio wave leakage issubstantial.

Frequency-divisionmultiplex-ing(FDM) typeCommunication zone: Communication zone of width 6.6 m X length 4.5 m or over is available.
Radio wave leakage: Designed to minimize the leakage, the (radio wave) leakage is limited.
Others: The communication zone is confirmed to have no effect from the neighboring antenna
with different frequency.

Time-divisionmultiplex-ing(TDM) typeCommunication zone: Communication zone of width 6.6 m X length 4.5 m or over is available.
Radio wave leakage: Designed to minimize the leakage, the (radio wave) leakage is limited.
Others: No uplink interference and practically no downlink interference were observed.
However, this system requires about twice longer time for communication.

Transmit/
receive antenna
separation typeCommunication zone: Communication zone of width 6.6 m X length 4.5 m or over is available.
Radio wave leakage: Substantial as the leakage is, there is little chance of communication
being made with the vehicle running on the neighboring lane because
the uplink communication zone is limited.
Others: Interference takes place when data are combined between the two antennas,
needing a circuit to avoid the interference.

Double-antenna
system

Triple-antenna
system

Evaluation

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: Single-antenna system: Double-antenna system

Receive power (dBm)-40

Center computer system-50

Lane controller
Transmission controller. Controller. Monitor. Backup memory unit
. HUB

-60
-70
-80

Onboard equipment
communication NG

-90
-100

Onboardequipmentsensitivity

Adjacent
lane
6

5

4

Lane for communication
3

2

1

0

-1

-2

License plate
number recognition unit

Adjacent
lane
-3

-4

-5

Camera 1-6

Roadside
RF unitRoadside antenna 1 Roadside antenna 2
f1

Width direction (m)Fig. 6 Radio wave (frequency) leakage to adjacent lane
Results of measurement of field intensity distribution in the directionof lane width using single-antenna and double-antenna systems(position in forwarding direction: 3 m)

License plate
number recognition unit

Roadside
RF unit

Camera 2

f2

Roadside antenna 1 area
Roadside antenna 2 area

results of field test of the double-antenna, frequencydivision multiplexing system. As shown in the figure,the communication zone shows excellent conformity
in simulation result and actually measured value,indicating that the desired communication zone has
been obtained.
Fig. 6 shows the measured (obtained) value of field
intensity in the direction of lane width. It has been
confirmed the double-antenna type has approximately
10 dB less leakage of radio wave (frequency) to theadjacent lane at the end of the lane than the singleantenna type, reducing the garbage communication(error communication) with the vehicles running on
the neighboring lane.
(5) Development achievement
The desired achievements could be obtained as shownin Table 3
3. Thus the RF communication unit was decided
to adopt the double-antenna, frequency-division multiplexing system to ensure the features given below.
(a) The present ETC antenna can be applied simply bychanging the installation conditions, ensuring highCamera 1 visual field
Camera 2 visual field
Cruising lane

Overtaking lane

Fig. 7 Schematic diagram of equipment configuration

cost performance.
(b) The frequency-division multiplexing system provides
the communication time equivalent to that of singleantenna type, ensuring high reliability even forvehicles running at high speed.
(c) Compared with single-antenna type, it has less leakage of radio wave to the adjacent lane, with extremely
low error communication with the other vehicle.
5.2 High-reliability technology(1) Duplexing system configuration
Unlike the conventional ETC system, the free-flow
ETC system requires non-stop round-the-clock unmanned operation. In order to realize this, the free-flow
ETC system was compared of the machines (devices)
shown in Fig. 7 to ensure high reliability.

Table 3 Achievements of development
Item

Target value

Reliability of communication(error rate)

10-6 or under(on radio lane: 10-5 or under)

Communication zone

Maximum speed

Radio wave (frequency)
leakage to the neighboring lane

Achievement
6
10 or under obtained(on radio line: 10-5 or under)

Remark-Width 6.6 m X length 4.5 m

Communication zone ofWidth 6.6 m X length 4.5 m
obtained

Double-antenna type,onboard equipment height: 1.0 m

90 km/h

90 km/h or moreAt the center of the lane

No communication madewith the vehicle running on
the neighboring lane
(left/right 3.5 m or above inthe direction of width)

The obtained onboard equipment receive power on theneighboring lane is -64 dBm
or under (the chance of communication being made with thevehicle running on the neighboring lane is extremely small).

-

Mitsubishi Heavy Industries, Ltd.
Technical Review Vol.40 No.3 (Jun. 2003)

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Table 4 Reliability at trouble occurrence
Trouble item

Reliability

Center computer system- Lane controller (transmission controller)
circuit trouble (error)

The lane controller can be operated as usual. The ETC service data, detailed ETC utilization data
and license plate number recognition data are stored in the lane controller (transmission controller)
to be transmitted to the center computer system once the system returns to normal state.

Circuit trouble inside the lane controller(transmission controller- license plate number recognizing unit)

The roadside RF unit constantly activates the roadside antenna to send RF communication data to
the transmission controller, so that the ETC service data and detailed ETC utilization data aretransmitted to the center computer system as usual.
The license plate number recognizing unit saves the recognized (detected) data and sends the data
to the transmission controller after the line returns to normal state.

Circuit trouble inside the lane controller(transmission controller - roadside RF unit)

The roadside RF unit stores the RF communication data to send it to the transmission controller after
the line returns to normal state.
The license plate number recognizing unit transmits the recognized data to the lane controller(transmission controller), so that the license plate number recognized data is transmitted to thecenter computer system in the usual manner.

Lane controller (license plate number
recognizing unit) trouble, camera trouble

The roadside RF unit transmits the RF communication data to the lane controller (transmission
controller), so that the ETC service data and detailed ETC utilization data are sent to the centercomputer system as usual.
The license plate number recognized data is not created because of the machine trouble.

Lane controller (roadside RF unit) trouble,
roadside antenna trouble

The system can be continuously operated in spite of the trouble occurrence in one of the RF units orin the roadside antenna. However, because of the characteristic of the roadside antenna, the lane at
the side end gets out of the communication zone.
The trouble in both roadside RF units and roadside antenna cripples the roadside system, making its
operation impossible.

Equipment maintenance

The roadside RF unit and the roadside antenna can be put to maintenance alternately to allow thesystem to continue operation. However, because of the characteristic of the roadside antenna, thelane at the side end gets out of the communication zone.

Further, the lane controller constantly monitors thecomponent machine, and should some error occur, it isinformed immediately to the remote monitor installedon the center computer system.
The likely error items and the reliability are summedin Table 4
4. The system is equipped with backup memory
at the local (individual) equipment, saving the data andensuring continuous operation even when something
goes wrong with the host equipment. The reliability oftoll collecting system has thus been greatly improvedby adopting the duplex equipment and having step-wisebackup memory.
(2) Function to prevent the user from being double charged
The free-flow ETC system adopts duplexing systemwith each of the roadside antenna having the communication zone covering 2 lanes. Thus, the onboard
equipment of a vehicle could make communication withanother antenna after completing communication withthe first roadside antenna, leading to the driver's getting double charged. In order to prevent this double
charging, the lane controller is installed to check theread data.

the service to allow the vehicles ETC transit through the
ETC of Kobe Municipal Road Corporation lying on the transit route from Kita Kobe Route No. 7 to Kobe Route No. 3
by improving the present transit function.
Further, this system is applicable not only to the off
ramps of urban expressways, but also to the newly constructed entrance gate/exit gate and as the unmanned tollcollecting system for other road public corporations andinstitutes.
Finally, the appropriate introduction of the free-flow
ETC system in the future will make it easy to adopt theroad pricing system and to allow a shift to diversified tollcollecting systems such as from the present open system
to closed system.

KOBE SHIPYARD & MACHINERY WORKS

Takeshi Hanabata

6. Conclusion

Yoshifumi Hayakawa

Shigehiro Hishikawa

TAKASAGO RESEARCH & DEVELOPMENT CENTER

The newly developed free-flow ETC system has started
operation at 4 exit gates since July 2002 as the transit ETC
system for Hanshin Expressway Public Corporation.
An ETC system for special zone toll collection, adopting
a new imaging system, is to be introduced by the end of the
fiscal year 2002. Further, the system is planned to expand

Masanori Tanaka

Mitsubishi Heavy Industries, Ltd.
Technical Review Vol.40 No.3 (Jun. 2003)

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