Connected and Autonomous Vehicles: The future? Contents

Appendix 7: CAV impact on congestion in the short, medium and long term

This Appendix summarises HERE’s description of the potential for connected and autonomous vehicles (CAV) to help—or hinder—congestion in the short, medium and long term.226

Short term (next 5 years)

There is already technology within cars that has been shown to offer benefits in terms of accident reduction and improvements in traffic efficiency (known as Advanced Driver Assistance Systems (ADAS)). The HERE report highlighted academic studies which analysed the benefits from the widespread adoption of existing Adaptive Cruise Control (ACC) systems, “showing how they can enable roads to operate at higher vehicle density and flow rates”. For example, in a study supported by Volkswagen, relatively low penetrations of ACC were found to “completely eliminate certain types of simulated traffic congestions”. However, other studies have been less optimistic, highlighting risks associated with mixed traffic scenarios where not all drivers are relying on ACC.

SBD Automotive forecast that by 2021, 17.5 million cars would be sold annually in the USA and Europe with applications like ACC and AEB, and that these would play a modest role in helping to alleviate traffic congestion.

Medium term (5–20 years)

The effect of the introduction of Level 4 autonomous vehicles on traffic congestion is much less predictable. In the medium term, there may be a number of possible negative effects on traffic congestion:

HERE notes that at this early stage “it is impossible to holistically quantify the positive or negative impact of highly autonomous cars”. The report also says that new vehicle ownership models and changing governmental policies “could play a role in counteracting some of these negative side-effects of congestion”. For example, car sharing “could become significantly easier when cars become more autonomous”, thereby possibly leading to a drop in vehicle ownership. Additionally, the Government could incentivise autonomy by setting up dedicated ‘Autonomous Lanes’, thereby “also preventing negative interactions with traditional cars and encouraging those individuals who have invested in autonomous technology to enjoy the benefits and become more comfortable with the technology”.

For the medium term, HERE concludes:

“Further studies and trials will be required to assess the dozens of autonomous use cases, hundreds of variables and thousands of scenarios in order to fully understand how traffic congestion will change. However, policy makers and the industry should fully recognize the many potential impacts that could accompany the positive benefits of highly autonomous vehicles.”

Long term (20–50 years)

The longer-term outlook for CAV is described as “paradoxically easier to forecast than the medium-term”. At some stage in the distant future (likely to be due to Government regulation), CAV will become ubiquitous and manual driving will be restricted. At this stage, the central management of all vehicle movements will become feasible, with both traffic accidents and congestion expected to be eliminated. However, HERE’s report acknowledges that “the value of debating how and when this will happen is limited”. Instead, attention must be given to “overcoming the medium-term complexities of managing mixed fleets of autonomous and traditional vehicles”.

226 HERE, How autonomous vehicles could relieve or worsen traffic congestion (2016): [accessed 28 December 2016]

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