Cost Benefit: There’s still life in the RSU

A mixture of mobile and static roadside units may be what’s required to fulfil the needs of connected vehicle communications
May 24, 2021 3 mins Read
By David Crawford
© Zlikovec |
© Zlikovec |

Worldwide, the operational road transport environment is becoming increasingly reliant on Vehicle to Everything (V2X) communications, not least in order to accommodate the emerging new generation of connected vehicles (CVs).

In the process, questions are arising as to the long-term commercial case for the continued deployment of the now well-established, DSCR-based roadside unit (RSU) - typically physically incorporated into the highway infrastructure - against alternative options.

The issue is the subject of a wide-ranging exercise recently carried out for the 5G Automotive Association (5GAA). The global body was formed in September 2016 to foster the development of ITS-based connected and self-driving cars.

Its claimed strength in the field lies in the achievement of close collaboration between the contributory automotive, technology, and telecommunications sectors.

At the core of this exercise are European consultant Ricardo Energy & Environment, working in association with Chemring Group subsidiary Roke Manufacturing.

Wide availability

The partners have analysed - from financial, business and marketing standpoints - four options that are widely available in Europe and the US for Vehicle to Infrastructure (V2I) deployment using direct and mobile network communications technologies. Three of these incorporate the continued use of RSUs.

The exercise highlights, as key factors in assessing the benefits and challenges of their deployment, the scale of standardisation activities that have been taking place across the European Union and in the US. These have served to reassure stakeholders of the ability of direct communications to support V2I priority use cases, a key factor sustaining road operator confidence in RSU deployment.

One factor cited is the absence of ongoing cellular data charges being incurred, with a number of road operators (ROs) giving high priority to their ability closely to control total, and continuing, costs. But a remaining issue is the restriction of the necessary connectivity to vehicles that are equipped with the corresponding communications technology. The lack of sufficient numbers of these has proved a barrier for some ROs as they consider transitioning to wide-scale deployment.

Even with OEMs such as Ford and VW making significant commitments for the future, the penetration of equipped vehicles into a developed country or region’s vehicle fleet is expected to be gradual over the next 10 to 15 years. This is being seen as limiting the benefits that can be achieved in the early stages of CV deployment.

Realistically, attaining RSU coverage of the entire major European road network is ruled out as being financially impracticable, resulting in a total cumulative cost of  €70bn (US$85bn).

Major stakeholders are also voicing concerns about the potentially high maintenance costs of the physical structure involved. The Netherlands Ministry of Transport, for example, has calculated the labour costs of ongoing RSU inspections and repairs at around €1,000 (US$1,200) per intersection, without accounting for the wider societal costs of closing roads while work is being carried out.

In response, one cost-effective emerging – and promising – approach takes advantage of the scope for the remote condition monitoring of installations, to avoid the need for routine on-site attendance. Running RSUs in a laboratory setting is already enabling some ROs to carry out substantial quantities of necessary work using office-based technicians.

Traffic safety

In the area of traffic safety, one line of inquiry sees potentially valuable roles for RSUs in managing future mixed traffic flows of connected and autonomous vehicles (C/AVs) and regular ones. When, for example, a C/AV is following one of the latter, it could well, in the absence of direct Vehicle to Vehicle (V2V) communications, take the former longer than a human driver would need to detect and respond to the movements of the driven vehicle ahead.

In one response, a joint exercise by US and Chinese engineers has envisaged a new role for RSUs in sensing the presence of vehicles that are moving within their areas of coverage. They would then be capable of delivering relevant beyond line-of-sight information to growing numbers of road users.

But overall costs remain a major factor, with the pure cellular deployment approach emerging as significantly cheaper in both Europe and the US. Despite some recognised performance challenges, some ROs are finding the currently-available levels of cellular performance adequate for their needs in terms of reliability and coverage.

Ricardo warns, however, that the higher costs noted as being initially incurred in opting for RSU-based options may, in the end, secure greater benefits overall. Variations in backhaul and cellular network availability are making it “very challenging to apply a common cost or technology approach across different deployment activities”.

Mobile prospects

Growing opportunities are also opening up for the routine deployment of new-style mobile RSUs (mRSUs) as alternatives, or additions, to the established static variety, to the limitations of which they can offer attractive money-saving solutions. It is likely, however, that more of them are going to be needed in any specific deployments – a cost factor in its own right that will need careful consideration.

Fleet vehicles such as freight trucks and (in urban contexts) buses are natural candidates for the role of hosting mRSUs. The fact that they are officially controlled by private- or public-sector organisations offers a high degree of operational security and guarantees authentication in advance of their being deployed. Again, they have the space to carry substantial amounts of communications equipment, offering greater memory capacity and back-up facilities.

Another positive factor is the fact that service buses run to fixed routes and schedules, enabling the accurate prediction of area coverage in terms of space and time, and of a sustainable level of service quality. They also realistically mirror real-life highway situations by moving in relation to traffic volumes, speeds and signals, stops, and road conditions and presence of other vehicles nearby.

© Chuyu |
© Chuyu |

Double-deckers also offer the advantage of height, offering better quality, and the highly-desirable line-of-sight delivery, of data in all directions.

Not least important in terms of maintenance costs, if the mobile unit breaks down, it can be conveniently and time-efficiently repaired or replaced at a central location, e.g. a bus depot, without the need for a call-out to a remote location.

Accordingly, Ricardo sees the most ideal, practical and economically satisfactory solution as one that brings together a mix of static (sRSUs) and mobile units. In this scenario, sRSUs act as the backbone of a stable and reliable roadside service, at night as well as during the day.

The addition to the mix of mRSUs serves to increase coverage, alleviate service bottlenecks, and reduce the total number of sRSUs that are needed to sustain a satisfactory level of performance, both during rush hours and at night and guarantees a minimum level of connectivity at regular intervals.

In summary, mRSUs will ensure a high quality of connectivity to vehicles that are travelling along in the same direction (or stuck together in a traffic jam), while sRSUs will guarantee a minimum level of connectivity at regular intervals along a given route. The smart use and positioning of both types will enable the filling of important complementary roles in the successful local implementation of V2I systems.

Examples include particular hazard points on road networks, e.g. at intersections, or when there is a need to maintain traffic efficiency.

Overall, the exercise concludes that the smart use and positioning of both sRSU and mRSU equipment will continue to fill important and complementary roles in the successful local implementation of vehicle communications systems across a spectrum of use cases.

Meanwhile, promising new prospects are emerging with the arrival of dual-mode/active RSUs, which are capable of broadcasting using both C-V2X and DSRC protocols at the same time, with no need for operators to make a specific choice either way.