V2X Tolling System for C-ITS Environments

Emanuel Vieira

1 a

, Tiago Dias

2 b

, Jo

ao Almeida

3 c

, Ana V. Silva

2 d

, Joaquim Ferreira

4 e

and Lara Moura

Instituto de Telecomunicac¸

oes, Departamento de Eletr

onica, Telecomunicac¸

oes e Inform

atica, Universidade de Aveiro,

Campus Universit

ario de Santiago, 3810-193 Aveiro, Portugal

A-to-Be Mobility Technology S.A., Lagoas Park, Ed. 15, Piso 4, 2740-267 Porto Salvo, Portugal

Instituto de Telecomunicac¸

oes, Universidade de Aveiro, Campus Universit

ario de Santiago, 3810-193 Aveiro, Portugal

Instituto de Telecomunicac¸

oes, Escola Superior de Tecnologia e Gest

ao de

Agueda, Universidade de Aveiro,

Campus Universit

ario de Santiago, 3810-193 Aveiro, Portugal

Keywords:

V2X Tolling, Electronic Toll Collection, Vehicular Communications, Connected Vehicles, Cooperative

Intelligent Transportation Systems.

Abstract:

Electronic Toll Collection (ETC) has several decades of history worldwide. Vehicle-to-everything (V2X)

communication technology is a more recent innovation but has been a central topic in the ITS community for

more than a decade now. However, V2X technology adoption in vehicles has been limited and applications are

mostly related to safety use cases. In this paper, V2X-based tolling applications are studied, as well as their

feasibility, and how these applications could be enablers of a more massive V2X adoption in vehicles. V2X

Tolling standards and solutions from SAE and ETSI are explored. A novel solution is presented, followed by

a comparison with previous proposals and standards. Finally, preliminary results from the proposed system

are presented and analyzed.

1 INTRODUCTION

Tolling is an industry with several decades of history

worldwide. It is used mostly to ﬁnance infrastructure

investment. The ease of use for customers provided

through the employment of different types of wire-

less communications, together with visual recognition

technology, has been the main driver for its modern-

ization.

In 2012, the European Union had a 72 000 km

toll road network with 60% covered by ETC at the

time (Council of the European Union, 2017). Most

of the ETC solutions were using microwave Ded-

icated Short Range Communication (DSRC) tech-

nology (Oh et al., 1999). Automatic Number Plate

Recognition (ANPR) (Patel et al., 2013), and, more

recently, satellite (GNSS) (Sal

os et al., 2013) and mo-

bile communications (GSM) (Lee et al., 2004) based

https://orcid.org/0000-0001-9466-4649

https://orcid.org/0009-0009-1785-7119

https://orcid.org/0000-0001-6634-6213

https://orcid.org/0000-0003-0328-1787

https://orcid.org/0000-0002-7471-5135

solutions also emerged.

V2X communication technology has enabled

communications between vehicles and with the in-

frastructure. It is a more recent innovation relative to

tolling but it has been a central topic in the ITS com-

munity for more than a decade now. However, V2X

technology adoption in vehicles has been limited and

the usage is mostly linked with safety use cases. Cur-

rent safety use cases may not be enough motivation

for the public that is more used to getting live traf-

ﬁc information and routing through mobile applica-

tions in smartphones. V2X Tolling positions itself as

a convenience use case, avoiding stops, cumbersome

manual payment systems, or simply the need to pur-

chase additional devices that operate on batteries that

need to be replaced from time to time. With V2X,

tolling may well be the right motivation for the public

to see value in such convenience use cases and trigger

the uptake of V2X in vehicles. ETC solutions have

proved very successful in European markets (Coun-

cil of the European Union, 2017), even though they

require the acquisition of dedicated On-Board Units

(OBUs) that typically need to be placed on the wind-

shield and require periodic battery replacement. V2X

Vieira, E., Dias, T., Almeida, J., Silva, A., Ferreira, J. and Moura, L.

V2X Tolling System for C-ITS Environments.

DOI: 10.5220/0011994000003479

In Proceedings of the 9th International Conference on Vehicle Technology and Intelligent Transport Systems (VEHITS 2023), pages 103-112

ISBN: 978-989-758-652-1; ISSN: 2184-495X

 2023 by SCITEPRESS – Science and Technology Publications, Lda. Under CC license (CC BY-NC-ND 4.0)

103

Tolling would provide the advantage of already com-

ing in the vehicle and not requiring any battery re-

placement.

V2X Tolling can also take advantage of its secu-

rity mechanisms to provide and ensure correct vehi-

cle characteristics for the transactions, eliminating the

need for vehicle classiﬁcation on the infrastructure

side. Similar mechanisms could be used for the ve-

hicle to assess and report its passenger occupancy as

part of High-Occupancy Tolling (HOT) scenarios.

Furthermore, the use of V2X communications

could enable a more ﬂexible tolling framework, with

the implementation of virtual tolling plazas that can

be dynamically moved inside the wireless range of

Roadside Units’ (RSUs) coverage areas according to

the needs of road operators or city managers. Simi-

larly, dynamic pricing could be easily implemented,

by varying the cost of tolling payments for the same

plaza throughout the day, e.g. based on road conges-

tion levels or other time-varying metrics, and adver-

tising this pricing information via nearby RSUs.

More recently, there has been a movement towards

the adoption of V2X devices for Vulnerable Road

Users (VRUs) (ETSI, 2020b), namely for those us-

ing lighter modes of transport such as bicycles. This

could pave the way for even more widespread adop-

tion of V2X fee collection or even V2X payments,

with the added beneﬁt of supporting a distance from

the payment receiver devices that NFC is not capable

of supporting.

In this paper, tolling applications using V2X com-

munications and their feasibility are explored. An

overview of the standardization efforts in the USA

by SAE (SAE International, 2022), and in Europe

by ETSI (ETSI, 2020a) is provided, complementing

these with a newly proposed solution based on the

ETSI ITS communication protocol stack for vehicular

communications. The proposed system includes two

distinct variants, one relying on TLS and TCP session

establishment (TLS-V2XT) and another one based on

the Geonetworking protocol and security framework

(GN-V2XT).

The rest of the paper is divided as follows. Sec-

tion 2 provides an overview of V2X Tolling stan-

dards and related work and implementations. Section

3 presents the proposed solution for V2X Tolling, its

architecture and describes the implementation options

taken in each protocol layer of the solution. In Sec-

tion 4, this solution is compared and contextualized

with standards and other implementations. Section 5

presents preliminary results of ﬁeld trials using the

proposed V2X Tolling solution. Finally, Section 6

concludes this paper by providing conclusions and an

outlook of the next steps.

2 RELATED WORK

V2X Tolling has been identiﬁed as a feasible use case

since the beginning of V2X communication systems

development (Li et al., 2011).

In 2020, ETSI published a pre-standardization

study on payment applications for Cooperative ITS

(C-ITS) using Vehicle-to-Infrastructure (V2I) com-

munications (ETSI, 2020a) based on the works of

(Randriamasy et al., 2019a) and (Randriamasy et al.,

2019b). This study presents different tolling and fee

collection scenarios such as plaza systems, free ﬂow

tolling, and other payment applications such as park-

ing, energy charging, ferries, and even drive-ins. It

then proposes a proof-of-concept V2X Tolling solu-

tion that ﬁts into the C-ITS stack and focuses on two

main aspects: high-accuracy vehicle location using

GNSS; and communication security. This is moti-

vated by the intrinsic differences between the typical

DSRC communications used for ETC and V2X com-

munications. DSRC communications for ETC use a

single device (antenna) for each lane, which is opti-

mized to communicate with only a single vehicle on

that lane at a time, while V2X has a much wider range

of up to 1 km. This means that, with DSRC, the lane

the vehicle is passing through is directly identiﬁed by

the receiving antenna and there is less chance for the

communication between the vehicle device and the

DSRC antenna to be interfered with. With V2X, the

location of the vehicle can be anywhere within the

large communication radius covered by the V2X de-

vice, and anyone within that radius can interfere with

those communications.

This proof-of-concept was implemented over

DSRC ITS-G5 V2X communications using IPv6,

TCP, and TLS to establish secure channels between

RSUs and OBUs. While the secure TLS channel

is used for the fee collection transaction itself, prior

to its establishment, RSUs broadcast open Service

Announcement Essential Messages (SAEM) (ETSI,

2019) which OBUs use to get information about the

RSU tolling functionality and to initiate the secure

channel.

This solution was trialed in France by the motor-

way operator SANEF on more than one hundred pas-

sages in Taissy and Senlis toll lanes, with 100% accu-

racy in detecting the correct toll lane of passage and

100% success in charging the transaction using V2X.

(ETSI, 2020a) positions V2X Tolling as a Value-

Added Service (VAS) within the V2X ecosystem, as a

standard solution adaptable to other standards such as

IEEE 1609.11 (IEEE, 2011) and identiﬁes it as having

the potential to provide a much more cost-effective

solution for ETC, with much simpler maintenance

VEHITS 2023 - 9th International Conference on Vehicle Technology and Intelligent Transport Systems

104

requirements than existing ETC infrastructures and

with the ability to expand into numerous other ser-

vices such as parking or drive-in purchases.

In parallel, in the United States, SAE published in

2022 the J3217 standard for V2X-Based Fee Collec-

tion (SAE International, 2022). It is a complete stan-

dard for V2X fee collection, implemented over the

WAVE protocol using either DSRC or C-V2X (PC5

interface) communications. J3217 focuses on V2X

Tolling use cases by dividing them into three main

scenarios:

• Road segment pricing – covering current main

road toll booth payment points, Multi-Lane Free

Flow (MLFF) / Open Road Tolling (ORT), and

High-Occupancy Tolling (HOT) scenarios.

• Closed network pricing – covering entry and exit

toll systems.

• Object pricing – covering the use of speciﬁc ob-

jects like tunnels, ferries, passes, or parks.

The standard moves from a high-level deﬁnition

of the entities involved in V2X Tolling and the rela-

tions between them to the deﬁnition of the actual com-

munications protocol using ASN.1 notation to deﬁne

three main message types:

• Toll Advertisement Message (TAM) – is transmit-

ted by RSUs to announce tolling point data in-

cluding toll zone geometry and fees.

• Toll Usage Message (TUM) – is transmitted by

the OBU in each vehicle to which a toll fee ap-

plies. It includes the necessary data for the Tolling

system to charge the road user.

• Toll Usage Message acknowledgment (TUMack)

– is transmitted by the RSU directed at a speciﬁc

vehicle / OBU to conﬁrm the TUM has been cor-

rectly received.

The protocol is designed to guarantee privacy and

security in TUM messages through the use of encryp-

tion, and has a general concern for privacy, through

the use of a rolling certiﬁcate mechanism for the OBU

encryption and signing of the messages.

The fee model supports different types of tariffs:

• Fixed fee by vehicle class/type, weight, or the

number of axles.

• Distance-based fees according to ori-

gin/destination also supporting different vehicle

classes/types, weights, or the number of axles.

• Time-based fees (like the ones used in car parks).

• Vehicle occupancy-based variations for the fees to

support High-Occupancy Tolling.

IEEE 1609.2 (IEEE, 2016) certiﬁcates are used for

signing TAM and TUMack messages, and for the sig-

nature and encryption of TUM messages, using 256-

bit or 384-bit Elliptic Curve Cryptography (ECC).

While ECDSA is used for signing, ECIES is used for

encryption purposes.

This standard also explores possible enforcement

techniques in a short appendix.

The last V2X Tolling scenario proposed in (SAE

International, 2022), referred to as ”object pricing”,

can be generalized from tolling to fee collection to in-

clude in-vehicle payments for on-street and off-street

parking, drive-through restaurants, pharmacies, fu-

elling, carwash, shopping pickup, and several other

types of in-vehicle provided services that can be paid

using V2X. This can easily become a mass conve-

nience service if the supporting infrastructure costs

are low and the vehicle uptake is high.

Recently, some works have introduced the use of

more emergent forms of cryptography to V2X-based

ETC systems like Distributed Ledger Technologies

(DLT), including blockchains, and Zero-Knowledge

Proofs (ZKPs) to enhance the security and privacy

of ETC systems. Assuring the position accuracy of

the vehicle is important to ensure that only the ones

passing through speciﬁed zones are charged. (Di-

douh et al., 2020) expands on this issue by propos-

ing a localization system based on distance estimation

through Received Signal Strength Indication (RSSI)

values analysis, and the recording of related Proof-

of-Location (PoL) data in a blockchain, where it is

further processed. (McEntyre and Kihei, 2022) pro-

poses a ZKP-based system to enhance user privacy

by preventing exploitation of vehicle location through

the use of continuous challenges issued by the RSU

to nearby OBUs that do not provide location data for

ETC purposes. Focusing on authentication and client

privacy, (Bartolomeu et al., 2020) uses the concepts

of Self-Sovereign Identity (SSI) and cryptocurrency

payments to provide mutual authentication between

OBU and RSU using ZKP, and then actually pay the

value of the toll due using a DLT, so that both pro-

cesses (authentication and payment) take place within

the tolling zone.

While these latter works can greatly enhance user

privacy by employing popular emergent technolo-

gies and techniques, the proposed solution focuses

on the OBU-RSU communications protocol using es-

tablished and faster cryptography schemes, similar to

what is being proposed within standardization bodies.

V2X Tolling System for C-ITS Environments

105

3 V2X TOLLING SYSTEM

In this paper, a new V2X Tolling system is pro-

posed. It is based on (ETSI, 2020a) but with cus-

tom Facilities-layer Tolling messages, named Tolling

Payment Messages (TPM), handled and generated by

a new Facilities sub-service named Tolling Payment

(TP). This TP service executes the tolling transac-

tions and transmits them over a secure channel based

on ITS-G5 V2X communications. It also employs

SAEMs for RSUs to announce the tolling service

and provide the necessary information for in-vehicle

OBUs to establish secure channels with the RSUs.

One of the protocol variants of this solution is

closer to (ETSI, 2020a) and uses TLS as a secure

channel for the exchange of TPM. This protocol vari-

ant is named TLS-V2XT.

Establishing a TLS channel over ITS-G5 involves

two additional network layers with TCP on top of

IPv6 (see Figure 1), which can add a signiﬁcant

amount of overhead trafﬁc, in some scenarios, to es-

tablish and maintain the channel (e.g., TLS nego-

tiation, TCP acknowledge messages, etc.). Taking

this into account and the fact that ITS-G5 already

has a powerful encryption feature usable within the

GeoNetworking protocol, a different approach is pro-

posed to V2X Tolling altogether. In this second ap-

proach, the same SAEM message is used but the

TLS channel is not established, being the TPM mes-

sages directly sent over BTP and GeoNetworking

with GeoNetworking’s native encryption and signing

features and implementing a retransmission mecha-

nism for messages that get no reply. This other proto-

col variant is called GN-V2XT.

While TLS-V2XT was implemented essentially to

assess the feasibility of (ETSI, 2020a) and study its

viability for free ﬂow scenarios, GN-V2XT was de-

signed as a novel approach, closer to the options taken

in other ITS-G5 protocols such as CAM, DENM or

IVIM.

Figure 1 shows the protocol stack for SAEM, GN-

V2XT, and TLS-V2XT in a single image. SAEM

are Facilities layer messages, using BTP and GeoNet-

working for the Transport and Networking layer, re-

spectively, and ETSI TS 103 097 in the Security part,

speciﬁcally for signing the messages at the network-

ing level. GN-V2XT uses the same stack options as

SAEM but also uses ETSI TS 103 097 Security for

encryption of TPM Facilities layer messages. TLS-

V2XT uses TLS for Security, TCP for Transport, and

IPv6 for Networking layers with the same TPM Fa-

cilities layer messages. All messages in both these

protocols use the ITS-G5 LLC for the Access layer

but could be adapted to employ C-V2X technology.

Facilities

Access

Transport

Networking

SA (SAEMs)

ETSI EN 302 890-1

CA (CAMs)

ETSI EN 302 637-2

TP (TPMs)

this work

BTP

ETSI EN 302 636-5-1

TCP

RFC 9293

GeoNetworking

ETSI EN 302 636-4-1

MAC

ETSI EN 302 663

LLC

IEEE/ISO/IEC 8802-2-1998

MQTT-based comms.

this work

Security

Management

TLS

RFC

8446

Payment

Security

Ops.

this work

Crypto

Ops.

ETSI TS

103 097

GN6ASL

ETSI EN 302 636-6-1

SAEM

GN-V2XT

TLS-V2XT

IPv6

RFC 8200

Applications

Encrypted tolling data

exchange modes

SA Mgmt.

ETSI EN

302 890-1

Figure 1: Protocol stack comparison between the two pro-

posed V2X Tolling schemes.

Both solutions (TLS-V2XT and GN-V2XT) are

examined in the following subsections for each proto-

col layer, identifying the differences between the two

protocols as well as their similarities.

3.1 Facilities

The Facilities layer handles and generates the

messages related to the toll service advertisement

(SAEMs) and the messages related to the toll transac-

tion (TPMs), which are common to both TLS-V2XT

and GN-V2XT.

3.1.1 Service Announcement

In order to make OBUs aware of nearby tolls, SAEMs

are continuously broadcasted by RSUs at a rate of 1

Hz, advertising an ETC service (ITS-AID = 1, as de-

ﬁned in ISO 17419). The radio channel used is ETSI

ITS-G5 SCH ( 5.9 GHz).

Tolling zones are included in SAEMs, encoded in

a new structure named Tolling Payment Info (TPI). A

TPI is composed by the ID of the tolling zone, the

tolling zone itself as a sequence of coordinates deﬁn-

ing a polygonal area, the trafﬁc ﬂowing angle, and the

toll type, which can be either entry, exit, or single.

RSUs in the vicinity of the tolling zones broadcast

the TPIs in their SAEM.

3.1.2 Tolling Payment Message (TPM)

A new ITS message type named Tolling Payment

Message (TPM) is introduced to enable V2X Tolling

services. It is based on a request-reply mechanism,

being initiated by the OBU which issues a TPM re-

quest when it enters a tolling zone, followed by a

VEHITS 2023 - 9th International Conference on Vehicle Technology and Intelligent Transport Systems

106

Single

zone

TPM REQ Single

TPM REP Single

SAEM TPI Single

- TPI ID

- Transaction nonce

- Client ID

- Client signature (optional)

- Confirmation code

- Transaction nonce

- Client ID

- Receipt (toll value)

- RSU signature (optional)

Figure 2: Single tolling system protocol.

TPM reply issued by the RSU. The protocol is im-

plemented at the ETSI ITS Facilities layer. All TPM

messages received and transmitted by the RSU and

OBUs are published in an MQTT broker, by a module

running in the Application layer, for mobile app and

cloud integration purposes. TPMs support both single

toll (ORT or plazas) and closed tolling systems.

In a single tolling system (see Figure 2), when the

OBU detects it is inside a tolling zone, it broadcasts

a single encrypted TPM request that can only be de-

crypted by the local RSU. This message includes the

TPI identiﬁcation number, a nonce that identiﬁes that

speciﬁc request, the client identiﬁcation number asso-

ciated with the tolling company, and an optional client

signature, which may or may not be mandatory de-

pending on the communication mechanism used, as

described in the next subsection.

The RSU replies with a single encrypted TPM

reply that can only be decrypted by the OBU. This

message includes a conﬁrmation code, depending on

whether the RSU accepted the request or not, the

nonce of the request, the client identiﬁcation number,

a receipt with the monetary value of the toll due, and

an optional RSU signature.

In a closed toll system (see Figure 3), upon enter-

ing the motorway, if the OBU detects that it is inside a

toll entry zone, it broadcasts an encrypted TPM entry

request that can only be decrypted by the local RSU.

This message includes the TPI identiﬁcation number,

a nonce that identiﬁes this speciﬁc request, the client

identiﬁcation number associated with the tolling com-

pany, and optionally, a client signature.

The RSU replies with an encrypted TPM entry re-

ply only decryptable by the OBU. This message in-

cludes a conﬁrmation code, depending on whether the

RSU accepted the request or not, the nonce of the re-

quest, the client identiﬁcation number, and a manda-

tory RSU signature. This TPM must be signed as it

will be used by the OBU as proof of entry.

Exit

zone

Entry

zone

TPM Entry REQ

TPM Entry REP

SAEM TPI Entry

TPM Exit REQ

TPM Exit REP

SAEM TPI Exit

TPM Entry REP

(Entry proof)

- TPI ID

- Transaction nonce

- Client ID

- Client signature (optional)

- Confirmation code

- Transaction nonce

- Client ID

- Receipt (toll value)

- RSU signature

- TPI ID

- Transaction nonce

- Client ID

- Client signature (optional)

- Entry proof

- Confirmation code

- Transaction nonce

- Client ID

- Receipt (toll value)

- RSU signature (optional)

Figure 3: Closed tolling system protocol.

Upon exiting the motorway, if the OBU detected

it is inside a toll exit zone, it broadcasts an encrypted

TPM exit request that can only be decrypted by the

local RSU. This message includes the TPI identiﬁca-

tion number, a nonce that identiﬁes this speciﬁc re-

quest, the client identiﬁcation number associated with

the tolling company, the entry proof and, lastly, an op-

tional client signature.

The RSU replies with an encrypted TPM exit re-

ply, only decryptable by the OBU. This message in-

cludes a conﬁrmation code associated with the RSU

having accepted or not the request, the nonce of the

request, the client identiﬁcation number, a receipt

with the monetary value of the toll due value, and an

optional RSU signature.

The entry proof acts as a way for the RSU to ver-

ify in which place the OBU has entered the motor-

way. All TPMs contains a timestamp which can also

be analyzed for entry/exit analysis to avoid malicious

behavior. In case the entry proof is not provided by

the OBU at the exit, the toll value due is to be deﬁned

in accordance with the tolling company’s policy.

V2X Tolling System for C-ITS Environments

107

3.2 Security

To safeguard client privacy, communication between

the OBU and the RSU must be encrypted. Authenti-

cation is also required to ensure that the RSU belongs

to a trusted tolling company and that the OBU belongs

to an authorized client.

At the security level, the two proposed schemes

(TLS-V2XT and GN-V2XT) follow different ap-

proaches with the same goal of providing secure TPM

exchange.

3.2.1 TLS (TLS-V2XT)

In TLS-V2XT, two different sets of certiﬁcates are

used. In the ETSI ITS protocol stack, vehicles and

RSUs must have by default a set of temporary cer-

tiﬁcates (set A) named Authorizations Tickets (ATs),

which act as pseudonyms. ATs provide authentica-

tion in the vehicular network, privacy, and unlinka-

bility through their short-lived timespan and rotatory

mechanism. These certiﬁcates are used for signing

SAEMs. A tolling company should, in principle, not

be able to link an AT with a user’s identity, there-

fore it must be able to authenticate users and RSUs

using a PKI of its own. This is achieved by using

another set of certiﬁcates, issued by the tolling com-

pany or tolling agency. This other set of certiﬁcates

(set B) is based on X.509 and is used to set up the

TLS channel. TLS provides encryption and authenti-

cation based on the tolling company’s PKI to secure

the TPM exchange. Both the client (OBU) and RSU

are mutually authenticated. The TLS channel is im-

plemented using OpenSSL.

3.2.2 GeoNetworking Security (GN-V2XT)

In GN-V2XT, as in TLS-V2XT, GeoNetworking pro-

vides authentication on the local vehicular network

by signing SAEM messages (ECDSA 256-bit) using

ATs (set A). For encryption and user authentication

of TPM messages, GN-V2XT employs a second set

of certiﬁcates (set C), inspired by the ETSI ITS PKI

and based on the ETSI TS 103 097 standard, as a sub-

stitute for set B. Set C is also produced by the PKI of

the tolling company or agency. The ECIES encryp-

tion scheme, implemented using OpenSSL, is used in

GN-V2XT to secure the TPM exchange.

3.3 Transport

The Transport Layer protocol used in each V2X

tolling system approach is different.

3.3.1 TCP (TLS-V2XT)

In TLS-V2XT, TCP provides a reliable communica-

tion channel. It is implemented using an adapted ver-

sion of an open-source TCP implementation. The

adapted version provides additional functionality as

well as support for IPv6 instead of IPv4.

To protect against packet loss, in TLS-V2XT the

TCP retransmission mechanism ensures the arrival of

timed-out packets when the transmitter does not re-

ceive an acknowledgment from the receiver. In this

implementation, the TCP timeout is set to 200 mil-

liseconds.

3.3.2 BTP (TLS-V2XT & GN-V2XT)

The Basic Transport Protocol (BTP) is used in

the Transport layer, to encapsulate SAEMs in both

schemes and to encapsulate TPMs in the GN-V2XT

approach. Since BTP does not have any retransmis-

sion features, in GN-V2XT a retransmission mecha-

nism of the TPM messages was implemented. The

OBU retransmits the TPM request after a timeout is

reached and until it receives the TPM reply from the

RSU. In this implementation, the timeout is set to 400

milliseconds. This retransmission mechanism is im-

plemented in the Facilities layer by the TP service,

and not in the Transport layer.

3.4 Network

The Network Layer protocol employed is distinct for

each V2X tolling system approach.

3.4.1 IPv6 (TLS-V2XT)

In TLS-V2XT, IPv6 provides addressing. A raw im-

plementation is used, capable of encapsulating and

decapsulating IPv6 packets with simple addressing

capabilities. Packet hopping is currently not imple-

mented.

3.4.2 GeoNetworking (GN-V2XT)

GN-V2XT uses GeoNetworking for the Networking

layer, as it is done for SAEMs. The encryption and

decryption of secure TPM packets happen in this layer

through requests to the Security service. Both the

TPM and the BTP header are encrypted.

4 SOLUTION COMPARISON

A comparison between the V2X Tolling solutions

TLS - ETSI TR (ETSI, 2020a), SAE (SAE Interna-

VEHITS 2023 - 9th International Conference on Vehicle Technology and Intelligent Transport Systems

108

Table 1: Overall comparison among the different V2X Tolling solutions.

Feature TLS-ETSI TR TLS-V2XT (this work) SAE GN-V2XT (this work)

Announcement SAEM SAEM TAM SAEM

Communications

Complexity (# messages)

13 7 3 3

Authentication TLS w/ ECC TLS w/ ECC ECDSA ECDSA

ETC application

certiﬁcates

ETSI TS

103 097-based

X509-based IEEE WAVE-based

ETSI TS

103 097-based

Encryption TLS TLS ECIES ECIES

Retransmission TCP TCP

On timeout after

TUM transmission

On timeout after TPM

request transmission

WAVE MAC

IEEE 1609.4

LLC

IEEE/ISO/IEC 8802-2-1998

Security

IEEE 1609.2

Crypto

Ops.

WSMP

IEEE 1609.3

Tolling

SAE 3217

Management

IEEE 1609.3

TUM/

TUMack

TAM

Applications

IPv6

RFC 8200

Service

Advert.

Network & Transport

MAC

TCP

RFC 9293

BSM

SAE J2735

Encrypted tolling data

exchange mode

Facilities

Access

Transport

Networking

SA (SAEMs)

ETSI EN 302 890-1

CA (CAMs)

ETSI EN 302 637-2

TP (TPMs)

this work

BTP

ETSI EN 302 636-5-1

TCP

RFC 9293

GeoNetworking

ETSI EN 302 636-4-1

MAC

ETSI EN 302 663

LLC

IEEE/ISO/IEC 8802-2-1998

MQTT-based comms.

this work

Security

Management

TLS

RFC

8446

Payment

Security

Ops.

this work

Crypto

Ops.

ETSI TS

103 097

GN6ASL

ETSI EN 302 636-6-1

SAEM

GN-V2XT

TLS-V2XT

IPv6

RFC 8200

Applications

Encrypted tolling data

exchange modes

SA Mgmt.

ETSI EN

302 890-1

Figure 4: Protocol stacks and supporting standards for SAE V2X Tolling vs. GN-V2XT + TLS-V2XT.

tional, 2022), and the two newly proposed variant

schemes is given in Table 1. The protocol stacks used

are also detailed in Figure 4. All designs follow the

same approach to communication logic: nearby RSUs

continuously broadcast the tolling service via SAEMs

or TAMs, and vehicles initiate P2P encrypted com-

munications with the advertising RSU when entering

a tolling zone. A small exception is a design in the

TLS-ETSI TR, where the RSU, after mutual authen-

tication, and when the vehicle enters the paying zone

(detected through trajectory analysis from Coopera-

tive Awareness Messages - CAMs - emitted by the

OBU), initiates the toll transaction by issuing a re-

quest for the client information.

Due to the multi-step message exchange in

TLS–ETSI TR, ﬁrst for the SAEM announcement

message (1 message), then the establishment of the

TCP (2 messages) and TLS (2 messages) sessions,

i.e., the handshakes, then for the authentication of the

vehicle for eligibility for the ETC service (2 mes-

sages), and ﬁnally for the actual exchange of the

payer information (5 messages and 1 ﬁnal conﬁrma-

tion message), this solution has the highest commu-

nication complexity, totalling 13 distinct messages.

The proposed TLS-V2XT implementation reduces

the communication complexity as only the TPM re-

quest and TPM reply are exchanged after the TCP

and TLS handshakes. Using ECIES, both in SAE and

in the GN-V2XT design, only two messages are ex-

changed, the TUM and TUMack, or the TPM request

and TPM reply, respectively. Communication com-

plexity is not related to the performance of the com-

munication scheme, as TLS has lower computational

requirements than ECIES due to lighter cryptogra-

phy. However, in scenarios with signiﬁcant packet

loss, communication performance can be severely de-

graded in designs with higher communication com-

plexity due to the higher probability of the need for

(more) packet retransmissions.

Authentication is provided by TLS using elliptic

curve cryptography (ECC) in TLS-ETSI TR and TLS-

V2XT or by ECDSA in the other implementations,

typically using 256 or 384 -bit curves. Separate sets

of certiﬁcates are used by the ITS-Station (ITS-S) for

authentication in the vehicular network during normal

operation and for authentication with the tolling sys-

tem. These sets are different in order to separate the

tolling service provider information from the user’s

vehicular data, thereby increasing user privacy.

User privacy is also enhanced by the encryption

V2X Tolling System for C-ITS Environments

109

used in the communication protocol, as personally

identiﬁable information must be communicated be-

tween the vehicle and the RSU to perform the toll

transaction. The general logic for establishing a pri-

vate and secure channel between ITS-Ss is similar

in both TLS and ECIES schemes: using the public

keys (asymmetric cryptography, slower) present in the

ITS-S certiﬁcates, the ITS-S derives an encryption

key (symmetric cryptography, faster) that is used to

encrypt the communication channel.

Given the possibility of packet loss, messages

must be retransmitted after a timeout. In the case of

the TLS designs, TCP safeguards packet delivery by

retransmitting packets if respective acknowledgments

are not received before a timeout. In SAE and on the

GN-V2XT design, the OBU retransmits the TUM and

TPM request, respectively, if the corresponding re-

sponses, the TUMack and TPM reply, are not received

before a timeout.

Although the SAE V2X Tolling standard rests on

top of IEEE WAVE protocol stack and both GN-

V2XT and TLS-V2XT (as well as the originating

TLS-ETSI TR) rely on a different one (ETSI ITS-G5),

there are more architectural similarities between SAE

V2X Tolling and GN-V2XT than between GN-V2XT

and TLS-V2XT. In both SAE V2X Tolling and GN-

V2XT, authentication, and encryption are handled in

the Network layer (using ECIES for encryption and

ECDSA for authentication in both cases) and retrans-

mission is the responsibility of the Application or Fa-

cilities layer.

As for the tolling protocol itself, TLS-ETSI TR

uses a more complex protocol than SAE V2X Tolling

or the newly proposed schemes. TLS-ETSI TR in-

cludes intermediate phases (vehicle tracking, etc.)

other than the transaction itself. It would be desir-

able to avoid the need for such phases and still be

able to use the tracking information from vehicles in

the vicinity of the tolling areas to distinguish between

passages in different lanes. This could be achieved

by having the RSU or the central system tracking ve-

hicles in the vicinity of the tolls using CAM or Basic

Safety Messages (BSM) and, once a transaction is ini-

tiated, fetch this information for a use or discard it if

it’s not used within a speciﬁed time interval.

It is important to note that the SAE V2X Tolling

standard is prepared for more payment scenarios than

the implementations proposed in this work, including

even features for HOT or other scenarios such as an

object or time-based fee collection.

Given the provided comparison, GN-V2XT and

SAE V2X Tolling are more lightweight than TLS-

V2XT and the original protocol used in (ETSI,

2020a), in respect to network usage, while providing

a higher degree of security. Meanwhile, both GN-

V2XT and SAE V2X Tolling have a higher process-

ing demand from RSUs for the encryption algorithm

than TLS used in TLS-V2XT and the original pro-

tocol used in (ETSI, 2020a). The main differences

between GN-V2XT and SAE V2X Tolling are the us-

age of different V2X stacks (ITS-G5 and WAVE re-

spectively) and the fact that the authorization scheme

in GN-V2XT is detached from the vehicular security

system running at lower levels of the communication

stack, which does not happen in SAE V2X Tolling.

This means that GN-V2XT is able to offer greater

control over authorized customers to tolling author-

ities, agencies and enterprises. This decoupling of

the vehicular security system and payment protocols

could potentially enhance the security and privacy of

the tolling system by reducing the likelihood of unau-

thorized access and protecting sensitive user informa-

tion.

5 PRELIMINARY RESULTS

The proposed solution was ﬁrst validated in labora-

tory tests, followed by three sets of road tests in Portu-

gal, two in the Aveiro region, and one in Lisbon. Both

GN-V2XT and TLS-V2XT variants were tested in the

laboratory and the ﬁrst Aveiro region trials, where

some preliminary results were obtained. Regarding

these ﬁrst Aveiro road tests, Figure 5 depicts the

tolling zone and RSU locations. The OBU and RSU

are both composed of a PC Engines APU3D4 featur-

ing an AMD GX-412TC 4-core CPU @ 1.4 GHz with

4 GB RAM and a Qualcomm Atheros AR928X Wi-Fi

module adapted for ITS-G5. The OBU and RSU used

in the tests were the only ITS-G5 transmitting stations

in the vicinity, surrounded by mild trafﬁc character-

ized in its majority by legacy (non-connected) vehi-

cles. The RSU was installed at a high point, decreas-

ing the probability of packet loss due to vehicles act-

ing as obstacles.

The results of three runs are provided in Table 2,

two for GN-V2XT (the average is provided) and one

for TLS-V2XT. During each run, the OBU passed

through the open system ﬁrst and then through the

closed system. The results are respective only to the

open system. The open system tests were successful

in this ﬁrst trial, but the closed system tests failed be-

cause the entry toll zone was set too far away from

the RSU that should be covering it, so there was no

adequate ITS-G5 coverage on the exit Toll. Only

the entry toll was adequately covered. This resulted

in the OBU being unable to initiate communication

with the RSU that should cover the exit toll. Follow-

VEHITS 2023 - 9th International Conference on Vehicle Technology and Intelligent Transport Systems

110

up tests with the closed system scenario in Lisbon

were successfully conducted, however, those results

are not presented in this work since TLS-V2XT was

not tested and the hardware used in those trials was

signiﬁcantly different in computational power, hin-

dering any fair comparison.

Table 2 presents the obtained results for both im-

plementations (GN-V2XT and TLS-V2XT), using an

OBU and an RSU in a single tolling system scenario

for the ﬁrst road trial. The delays presented are mea-

sured from the time the OBU detects it is inside a

tolling zone up until the instant it receives and ﬁnishes

analyzing the TPM reply.

The results show the feasibility of the employed

communication mechanisms and the proposed tolling

system based on TPM messages. The measured de-

lays are all below 200 ms, which is sufﬁcient for a

non-safety vehicular service such as tolling.

The proposed GN-V2XT variant is on par with

the TLS-V2XT scheme in terms of communication

latency.

However, the TLS option lacks some security fea-

tures related to authentication during both the TCP

and TLS handshakes, i.e., handshake messages are

not authenticated, potentially enabling some types

of denial-of-service attacks. This scheme also has

a higher communication complexity as 7 messages

are exchanged (1 for SAEM announcement, 2 for the

TCP handshake, 2 for the TLS handshake, and 2 for

the secured TPMs).

In the GN-V2XT scheme, which uses heavier

cryptography (ECIES), only 1 SAEM announcement

message and 2 TPM messages are exchanged (the se-

cured pair of TPM request and reply), which can be

beneﬁcial in higher packet loss scenarios. The use of

ECIES is also more in line with the ETSI ITS stan-

dards which are employed in other V2X applications

(i.e., certiﬁcate requests to CAs). Ultimately, ECIES

is much more widely deployed in commercial ETSI

ITS OBUs/RSUs than TLS is.

More systematic testing with hundreds of repeti-

tions in both schemes is required for a more thorough

analysis.

Figure 5: Single tolling scenario used for the ﬁrst road trial.

Table 2: V2X Tolling delay in a single zone scenario.

[t]

Transaction delay (ms)

GN-V2XT 94.991

TLS-V2XT 79.197

6 CONCLUSIONS & FUTURE

WORK

This paper has shown that V2X Tolling is not only

possible but also can be the enabler for mass mar-

ket adoption of V2X technology. Meanwhile, ETC

DSRC technology still shows interoperability issues.

V2X could position itself as a fully interoperable

tolling solution to overcome these barriers and make

V2X Tolling as universal as credit card payments are

today. V2X Tolling could also have the added beneﬁt

of being able to provide proof of vehicle classiﬁcation

and other data elements such as passenger occupancy.

This work analysed the US Standard from SAE

(SAE International, 2022) (for IEEE WAVE and C-

V2X) and several working prototypes (using ETSI

ITS-G5) documented in (ETSI, 2020a) and in this pa-

per. All of these have adopted strong security mech-

anisms and use retransmission mechanisms to ensure

message delivery over unreliable vehicular communi-

cations channels.

In this paper, two main V2X Tolling approaches

using ITS-G5 were presented: TLS-V2XT and GN-

V2XT. TLS-V2XT is based on TLS-ETSI TR (ETSI,

2020a) and uses a TLS channel setup over ITS-G5

using TCP and IPv6. GN-V2XT uses a custom re-

transmission mechanism over the existing ITS-G5

stack with BTP for Transport and GeoNetworking

for Networking and Security. Both use TPM, a cus-

tom set of Facilities-layer messages, for the tolling

transactions. GN-V2XT shares with SAE (SAE In-

ternational, 2022) the options for Security protocols

(ECDSA and ECIES), the custom retransmission of

messages, and the reduced number of messages ex-

changed in a tolling transaction (only three packets

are transmitted when there is no packet loss).

Initial trials have been carried out with the pro-

posed schemes, but these are not yet sufﬁcient to

benchmark the two protocols and validate the success

rate on large volumes of trafﬁc. Setting up bench-

marking and larger-scale trials are the next mile-

stones. For now, it was possible to show the trans-

action times are below 100 milliseconds and how a

RSU with a slower CPU will take longer to process

GN-V2XT than TLS-V2XT due to the higher CPU

demand of the encryption used in GN-V2XT.

After extended tests of both GN-V2X and TLS-

V2XT over ITS-G5, it is also planned to implement

V2X Tolling System for C-ITS Environments

111

and test both over C-V2X and NR-V2X, in order to

benchmark the results against ITS-G5 technology.

With a solid standard in the US, the next natural

steps for V2X Tolling would be to develop and adopt

a standard in Europe, to progress with larger ﬁeld tri-

als, and to gather momentum with automotive manu-

facturers and infrastructure operators, paving way for

a wider adoption.

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