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Intelligent Transportation Systems Using External Infrastructure: A Literature Survey

Christian Creß, Zhenshan Bing, Alois C. Knoll

arXiv:2112.05615v4cs.ROcs.DC

TL;DR

Transportation problems including accidents, congestion, and pollution motivate interest in external-infrastructure ITS, but the paper identifies a lack of systematic surveys of existing systems. The authors review and classify implemented ITS projects, finding that current systems can provide highly accurate real-time information about individuals in traffic situations.

  • Problem

    The paper identifies no systematic survey detailing existing external-infrastructure ITS hardware, software, and value-added contributions, alongside outstanding questions about their purposes, sensors, services, and requirements.

    Source: §I · p. 2, §IV · p. 11

  • Method

    The authors review ITS documents from 2009 onward, categorize systems by development stage, and compare their sensors, system characteristics, and value-added contributions.

    Source: §I · p. 2, §III · p. 3

  • Results

    Current ITS can deliver highly accurate real-time information about individuals in traffic situations.

    Source: §V · p. 14

  • Takeaways & Limitations

    Further research should improve traffic-perception reliability and support plug-and-play mechanisms and secure decentralized real-time data distribution.

    Source: §V · p. 14

    Operational-maneuver and vehicle-control services are mainly covered by cordoned-off testbeds, not modern systems on public roads, and digital-twin information still has gaps in market-ready products.

    Source: C. Value-Added Services · p. 13

Abstract

from arXiv · show

The main problems in transportation are accidents, increasingly slow traffic flow, and pollution. An intelligent transportation system (ITS) using external infrastructure can overcome these problems. For this reason, the number of such systems is increasing dramatically, and therefore requires an adequate overview. To the best of our knowledge, no current systematic review of existing ITS solutions exists. To fill this knowledge gap, our paper provides an overview of existing ITS that use external infrastructure worldwide. Accordingly, this paper addresses current questions and challenges. For this purpose, we performed a literature review of documents that describe existing ITS solutions from 2009 until today. We categorized the results according to technology levels and analyzed its hardware system setup and value-added contributions. In doing so, we made the ITS solutions comparable and highlighted past development alongside current trends. We analyzed more than 357 papers, including 52 test bed projects. In summary, current ITSs can deliver accurate information about individuals in traffic situations in real-time. However, further research into ITS should focus on more reliable perception of the traffic using modern sensors, plug-and-play mechanisms, and secure real-time distribution of the digital twins in a decentralized manner. By addressing these topics, the development of intelligent transportation systems will be able to take a step towards its comprehensive roll-out.

I. INTRODUCTION

Transportation faces accidents, congestion, and pollution, while ITS using external infrastructure are presented as a possible response. The paper surveys these systems worldwide because prior reviews lacked technical detail and clear selection criteria.

I. INTRODUCTION

  • Accidents, traffic jams, and exhaust pollution motivate investigation of advanced traffic-optimization solutions, with these problems especially acute in cities.The introduction notes that half the world’s population lives in cities and projects a further two-thirds increase in urban population by 2050.Source: §I · p. 1
  • External-infrastructure ITS are presented as a possible way to address transportation problems and support services such as hazard warnings and traffic synchronization.The introduction also describes coordination with public transport and data exchange with vehicles equipped with driver-assistance systems.Source: §I · p. 1
  • The paper identifies a lack of systematic surveys detailing existing external-infrastructure ITS hardware, software, and value-added contributions.It instead reviews the last decade, summarizes historical development, and surveys technologies, trends, and open questions without treating specific ITS topics in depth.Source: §I · p. 2
  • The review covers ITS documents from 2009 onward, categorizes test fields by functionality, and extracts sensor and value-added-service characteristics to compare systems.It also considers earlier documents relating to the first use of ITS and situates systems across North America, Europe, and Asia.Source: §I · p. 2

II. METHODOLOGY

The review combines multilingual searches, explicit inclusion criteria, and a staged classification to compare implemented ITS projects. It extracts system characteristics and synthesizes qualitative and quantitative trends.

II. METHODOLOGY

  • The review follows Kitchenham’s systematic-review method after an initial exploratory scan of English-, German-, and Chinese-speaking ITS developments.Searches used IEEE Xplore, Google Scholar, and Google with multilingual keywords, related-work references, and both papers and gray literature.Source: §II · p. 2
  • Included systems use external sensors or infrastructure and were implemented in real-world scenarios; the review mainly selects documents from 2009 onward.Exceptionally important first-known test-field projects were also included for historical background.Source: §II · p. 2
  • The authors classify systems as “Early Days,” “Situation-Related Analysis,” or “Creation of Digital Twins” according to general features and functionalities.The passage names Table I as the location of the category definitions but does not provide those definitions.Source: §II · p. 2, Table I · p. 2
  • For comparability, the review extracts sensors, test-stretch length, overall architecture, and scientific novelty, then visualizes qualitative and quantitative findings and development trends.The synthesis is intended to provide an impression of current development and anchor points for open research questions.Source: §II · pp. 2–3

III. RESULTS

The review analyzed 357 papers on external-infrastructure ITS and summarizes the qualifying systems in a results overview. Its search strategy capped Google and Google Scholar results at the first 30 per search.

III. RESULTS

  • 357 papers on external-infrastructure ITS were analyzed using IEEE Xplore, Google Scholar, and Google searches with the stated keywords.For Google and Google Scholar searches yielding more than one million hits, the authors considered only the first 30 search results.Source: §III · p. 3
  • Table II lists useful-document counts for each keyword and search engine, with a topics filter noted for the table.The supplied passages do not state the table’s cell values.Source: §III · p. 3, Table II · p. 3
  • The review presents a complete overview of qualifying ITS results in Table III and describes systems grouped into its three development stages.The stages are “Early Days,” “Situation-Related Analysis,” and “Creation of Digital Twins.”Source: §III · p. 3

A. Early Days

Early external-infrastructure ITS progressed from safety and traffic-efficiency concepts to systems that analyzed traffic and interacted with participants. Projects explored vehicle-infrastructure communication, traffic management, and hazard warnings.

A. Early Days

  • PROMETHEUS and PATH were early projects that helped start ITS development, emphasizing road safety, traffic efficiency, and infrastructure-vehicle communication.PROMETHEUS-era in-vehicle sensors supported environmental awareness and hazard-warning concepts, not control of drivers through autonomous driving.Source: A. Early Days · p. 3
  • PATH equipped highways with sensors and control units to influence vehicle control and optimize traffic flow.A 1992 platooning experiment used Doppler radar; implementation near the millennium was considered infeasible at the time because of technical deficiencies and lack of public political acceptance.Source: A. Early Days · p. 3
  • DynaMIT used freeway counting loops to measure traffic load and generate real-time forecasts that supported dynamic route guidance.The Los Angeles concept was implemented using freeway counting loops in 2006.Source: A. Early Days · p. 3
  • SAFESPOT deployed road-side units across multiple European settings to enable vehicle-infrastructure communication and advance driver perception of surrounding vehicles.The system created local dynamic maps and a safety-margin assistant to detect critical situations in advance.Source: A. Early Days · p. 3

B. Situation-Related Analysis

Situation-related ITS analyze specific traffic conditions and deliver targeted information or services, rather than only describing general traffic flow. Across the reviewed projects, approaches range from distributed sensing and cooperative warnings to edge/cloud processing and vehicle-infrastructure communication.

B. Situation-Related Analysis

  • Compass4D combined road-hazard warnings with a situation-adapted traffic light that gave arriving cars speed recommendations.The project installed 147 RSUs and five backend offices across seven European cities.Source: B. Situation-Related Analysis · pp. 3–4
  • ICSI used a decentralized horizontal architecture for traffic-flow analysis in Lisbon and parking guidance in Pisa, with scalability identified as an advantage.Lisbon cameras also detected anomalies, while Pisa sensors supported work aimed at reducing air pollution.Source: B. Situation-Related Analysis · p. 4
  • FED4FIRE+ reported 10–15 ms latency and improved infotainment quality of service using RSU-collocated edge platforms; Diginet-PS processes sensor data at RSUs and in a cloud system –.Diginet-PS uses cloud data to store, analyze, and predict test-bed-wide conditions.Source: B. Situation-Related Analysis · p. 4
  • ConVeX combined induction-loop and connected-car data to provide safety warnings through road-user messages, gantries, and a smartphone app for vulnerable groups.The two German deployments implemented emergency braking, do-not-pass, blind-spot, and vulnerable-road-user collision warnings.Source: B. Situation-Related Analysis · p. 4
  • DRIVE-Testfeld Hessen used more than 120 RSUs for hazard warnings, shockwave damping, and GLOSAR, and hosted projects on services and cooperative-system assessment,, –.These included simTD, CVIS, and DRIVE C2X.Source: B. Situation-Related Analysis · p. 4
  • Kassel’s system prioritizes public transport and emergency vehicles and warns road users about approaching emergencies, while Midlands Future Mobility supports cooperative 3D object detection,, –[44].The Kassel system uses DENM for V2V and V2X communication; Midlands spans 300 kilometers across urban, rural-road, and motorway settings.Source: B. Situation-Related Analysis · pp. 4–5
  • The 2013 European Cooperative ITS Corridor supported infrastructure-assisted vehicle communication on Rotterdam–Frankfurt–Vienna; Austria’s 2016 Eco-AT set up a central ITS station and RSUs, with decentralized applications including roadwork warnings, speed restrictions, and intersection safety,.Source: B. Situation-Related Analysis · pp. 5–6

C. Creation of Digital Twins

Infrastructure-based ITS create real-time digital twins by combining sensor observations across stations. The surveyed test beds apply this approach to connected and automated driving, using varied sensors, communication links, and processing setups.

C. Creation of Digital Twins

  • Infrastructure-generated digital twins can provide ground truth for autonomous vehicles, while AIM targets real-time digital twins with video scenes in an urban test bed.AIM spans 7 km and connects 35 signalized intersections; its RSUs use radar, cameras, stereo cameras, and lidar or laser scanners.Source: C. Creation of Digital Twins · pp. 7, 9
  • 5GMOBIX test beds across Europe and Asia addressed distinct connected-mobility applications, including automated maneuvers, platooning, collision avoidance, infrastructure-assisted driving, and remote driving.The deployments combined MEC or cloud resources with differing sensor and RSU setups.Source: C. Creation of Digital Twins · pp. 8–9
  • Providentia fused camera and radar detections into local RSU twins, then combined them at a backend into a global digital twin across measuring points.Providentia++ extended the test bed into urban areas, with seven stations and 75 sensors over 3.5 km; its stable high-precision twin data stream was made public.Source: Figure 2 · p. 8, C. Creation of Digital Twins · p. 9
  • Baden-Württemberg’s test bed uses camera-based tracking to generate traffic twins in real time, and permits radar and lidar extensions for testing vehicle systems under real traffic conditions.CARAMEL research there addresses vehicle cybersecurity using artificial intelligence and machine learning.Source: C. Creation of Digital Twins · p. 9
  • ALP.Lab used more than 100 sensors to create digital twins near Graz and tracked vehicles for more than 2 km.Its goals included extending vehicle perception range and providing ground truth for plausibility checks of vehicle sensor data.Source: C. Creation of Digital Twins · p. 10
  • HEAT achieved its goal of networking an automated electric-minibus fleet with traffic infrastructure, using roadside sensors to support real-world environment perception.Its 2 km Hamburg test bed used several RSUs, radars, and lidars.Source: C. Creation of Digital Twins · p. 10

IV. DISCUSSION

The discussion identifies open questions about ITS purposes, sensor requirements, value-added services, and non-functional requirements. It emphasizes growing system complexity alongside privacy and security considerations.

IV. DISCUSSION

  • As ITS sensors and services become more demanding and complex, the systems must also account for privacy and security to achieve political acceptance.The survey identifies these as requirements for future uses of infrastructure-based ITS.Source: §IV · p. 10
  • Modern ITS rely on varied sensors alongside V2X, with cameras and lidars increasingly prominent and classic induction loops rarely considered.The figure caption describes this as a trend toward optimal traffic perception.Source: Figure 4 · p. 11
  • The survey frames four unresolved questions: ITS purpose trends, necessary sensor setups, existing and needed value-added services, and non-functional requirements.It notes that these questions have not yet been adequately answered.Source: §IV · p. 11

A. General Purpose Trend

ITS have developed from general traffic-flow improvements to analysis of individual situations and, increasingly, high-precision digital twins. The survey reports continued digital-twin test-bed growth and apparent stagnation in Situation-Related Analysis.

A. General Purpose Trend

  • Early ITS improved traffic safety and flow at a general level, while the first V2X prototypes were developed between 1986 and the 2000s.The subsequent Situation-Related Analysis category interpreted individual traffic situations and shared results with participants.Source: A. General Purpose Trend · p. 11
  • Situation-Related Analysis grew exponentially from 2010 to 2018 and then stagnated, while digital-twin test beds have continued to grow since 2012.The paper says the earlier category’s functional scope may no longer be sufficient.Source: A. General Purpose Trend · p. 11
  • Digital twins enable high-granularity traffic analysis, a development the paper calls necessary as future ITS are expected to give control recommendations to autonomous vehicles.Figure 3 presents cumulative test-bed numbers in each category.Source: A. General Purpose Trend · p. 11

B. Sensor Setup

Sensors shape ITS service precision and quality. The survey describes a shift from induction loops toward cameras and multisensor setups, while identifying vehicle-sensor integration as an area needing further research.

B. Sensor Setup

  • Sensors are the first process-chain step and have a main impact on the precision and quality of ITS services.Induction loops alone do not support individual situation analysis.Source: B. Sensor Setup · p. 11
  • Cameras support complex situation analysis, but perform unreliably at night or in extreme weather, so modern ITS combine them with radar, lidar, or specialized inputs.V2X technology has remained present throughout ITS development.Source: B. Sensor Setup · p. 11
  • Vehicle cameras, radars, and lidars receive too little attention in digital-twin fusion; integrating mobile sensor stations, especially through early sensor fusion, needs further research.The passage notes that vehicle sensors could be part of the ITS sensor setup.Source: B. Sensor Setup · p. 11

C. Value-Added Services

ITS value-added services should make traffic data useful in daily life, with potential benefits including lower maintenance costs, reduced pollution, faster transfers, and protection of human life. The surveyed services span traffic control and guidance, while the review identifies gaps in operational maneuvers and public-road control services.

C. Value-Added Services

  • ITS services are intended to turn traffic data and digital twins into practical benefits, including lower maintenance costs, reduced pollution, faster transfers, and protection of human life.The authors also note potential for high sales to help cover installation and maintenance costs.Source: C. Value-Added Services · p. 11
  • The service inventory covers traffic-flow control and lists test beds against service categories, including parking guidance, route control, speed advice, signage, shockwave damping, and priority or lane management.The table notes N/A where information could not be found.Source: C. Value-Added Services · p. 12, Table IV · p. 12
  • Systems supporting vehicle control have grown steadily since 2012, while growth in road-condition and hazard warnings has not followed a similarly strong continuing trend.Warnings rose sharply from 2015 but declined significantly from 2018 onward.Source: Figure 5 · p. 13
  • Operational maneuvers and vehicle-control services remain deficient on public roads, where the reviewed systems do not cover areas mainly addressed by cordoned-off test beds in China and the United States.Projects create digital twins to support autonomous driving, but gaps remain in using that information in market-ready products.Source: C. Value-Added Services · p. 13

D. Non-functional Requirements

ITS must remain reliable in extreme scenarios and include mechanisms for safety and cybersecurity. Nationwide rollout also depends on scalability, adaptability, and real-time capability, but the performance of distributed systems processing digital twins at high data density remains unclear.

D. Non-functional Requirements

  • ITS decision support requires extreme operational reliability, including in natural disasters, and the authors call for self-diagnostic and self-healing functions to support safe operation during malfunctions.The paper treats ITS as critical infrastructure requiring safety and cybersecurity mechanisms.Source: D. Non-functional Requirements · p. 13
  • Vehicle-to-test-bed communication is largely unencrypted, and secure transmission of high data volumes such as detailed digital twins remains an unresolved research need.The review describes encryption, priority-based authentication, and secure-communication approaches, but says cybersecurity challenges are not definitively solved.Source: D. Non-functional Requirements · pp. 13–14
  • Nationwide rollout requires scalability, adaptability, and real-time capability, yet it remains unclear how distributed ITS performs with digital twins in high-data-density environments.The cited ICSI test bed analyzed specific situations but did not process digital twins in real time.Source: D. Non-functional Requirements · p. 14

V. CONCLUSION

The survey filtered a collection of 357 papers and documents to analyze 127 sources, including 52 test bed projects. It reports increasingly complex and functional ITS that can provide highly accurate real-time traffic information, while identifying reliability, scalability, security, and service development as remaining challenges.

V. CONCLUSION

  • After collecting 357 papers and documents, the survey analyzed 127 filtered documents, including 52 test bed projects, tracing ITS development from early systems to digital twins.The review focuses on ITS using external infrastructure.Source: §V · p. 14
  • Current systems can deliver highly accurate real-time information about individuals in traffic situations, but improvements in overall reliability, scalability, and security are still needed.The authors identify more reliable traffic perception, modern sensors, plug-and-play mechanisms, and secure decentralized real-time distribution of large data volumes as research directions.Source: §V · p. 14
  • The authors characterize ITS development as progressing toward autonomous driving, while noting that questions remain before comprehensive rollout.Source: §V · p. 14
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