Reviewer's comments followed by author's response (AR) in square brackets .
Author’s response to reviewer Professor John Parkin.
This is a very interesting paper. I have only a few minor comments which the author may wish to consider.
- The following phrase in the abstract “including diversion of local trips to new major road capacity” does not quite make sense. Can this be re-phrased? Should the ‘to’ be deleted and a comma inserted? Sandwiching changed capacity between two phrases which allude to road use does not quite make logical sense.
[Author response: text amended.]
- It would help the reader if a short signposting paragraph outlining the structure of the remainder of the paper could be provided at the end of the introduction.
[AR: text added.]
- Is it worth spelling out the source of information on “the ability to detect vehicle speeds”. The reader could be forgiven for thinking this is satellite based as well, but in fact it is based on mobile telephony (I think).
[AR: I have replaced ‘detect’ by ‘infer’. My understanding is that speed is inferred from the rate of progress of the location detected by GPS, although the precise mechanism is not important in the present context.]
- Can the methodologies used by TomTom and Garmin to garner speed data be made more explicit? (So seemingly my comment about mobile telephony above is perhaps not exactly accurate).
[AR: see my comment above.]
- Is not the logical precursor to the phrase “the impact on the functioning of the road network as a whole” some statement about the ‘choices made by drivers using route guidance’? I assume some drivers may still think they ‘know best’. I also assume mistakes are made in trying to follow route guidance advice.
[AR: I have added a reference to providing better choices for road users to the highlighted paragraph.]
- Whilst I have not checked the literature, and I can believe that it is sparse, would not a normal way to demonstrate sparsity be to cite papers that are close to topic, but which do not in fact properly cover the topic at hand? Another part of me is surprised that there is sparsity in the literature, and I suspect most readers may assume that same. On this basis, I think it would be good for you to ‘cover your back’ on this one and provide some sort of evidence of the sparsity in the manner suggested.
[AR: my conclusion that the literature is sparse is based on extensive monitoring of a wide range of sources over time. In the text I provide an example of a TRID search for papers mentioning Waze.]
- Is there a particular methodological driver behind the phrase ‘systematic manner’? If not, does it really convey anything other than the paper is going to be well structured? In fact, the methodology seems to be revealed very soon after this phrase viz: ‘in respect of which published traffic data are relatively extensive’. It is hard for the reader to see the systematic nature of the paper, especially without a short signposting paragraph about its structure (see comment above).
[AR: I have replaced ‘systematic’ with ‘structured’.]
- The following sentence feels more like a conclusion than something for the introduction “It is suggested that there is considerable scope for the better management and…”
[AR: I have replaced ‘It is suggested that…’ with ‘It will be argued that…’]
- It is not quite clear what this sentence is driving at: “It would have been desirable to have had a comparative analysis of the previous and the new samples, to gain insight into what has been happening on the minor road network.” I presume the basis of the new sample is that it is a more balanced representation of sites with larger and also smaller traffic flow increases. Does this presumption need stating for your logic to be explicit? Also then, it may be that you can be more yet more explicit and suggest what a comparison may have revealed. I guess it may have revealed the types of route that have experienced the greatest traffic growth. So, all up, I think I am asking if you can make clear what you think such an analysis could have revealed, rather than just saying that it is ‘regrettable’ that this was not done. You do say there remains therefore uncertainty about the ‘nature and causes’ of the change. Would such an analysis actually have been able to reveal the causes? It would be good, as indicated above, if you can indicate what you mean by nature.
[AR: I have clarified the text.]
- The TfL ‘case study’ is revealing and quite dramatic!
- Can the following phrase be safely deleted from the end of the sentence in which it sits: “as well as extending such local knowledge”?
[AR: My experience is that use of satnav can extend local knowledge of minor roads.]
- You give a reason for heterogeneity of growth on minor roads being linked with congestion on the adjacent major road. However, surely one of the most significant reasons for heterogeneity would be network geography. Some minor roads will be beneficial for through traffic to use, while other will not be beneficial for through traffic to use. Does this point need mentioning?
[AR: text amended to reflect this consideration.]
- Can a citation be provided for “the available evidence from [their] responses” around the importance to travellers of knowledge about ETA? Is there a more robust example of revealed preference valuations from the literature than Costley and Gray?
[AR: I am not aware of citable evidence other than Costley and Gray. There was an earlier DfT study, which is no longer visible. I have participated in discussions of the impact of congestion that are consistent with the conclusion stated. I have amended the text to recognise the limited evidence available.]
- The reader would like to know a little more precisely what Derrow-Pinion found.
[AR: I have amplified, although it is hard to understand the AI methodology.]
- Is it the case that ‘commonly older vehicles are tested annually’? I thought MOTs were every three years.
[AR: the MOT is annual after the third anniversary of a vehicle’s registration.]
- In the discussion, the reader felt slightly cheated that you did not spell out in a little more detail what the regulatory regime may look like. Do you think it possible tat this aspect can be expanded upon?
[AR: I have added a short paragraph in the Discussion.]
- I am sorry if I missed it, but are there implications for traffic modelling? Do current route assignment algorithms need to be revisited, or do they remain robust? Minor road trip diversion suggests a need for perhaps a greater network refinement than may in fact exist in some traffic models.
[AR: the penultimate paragraph refers to traffic modelling.]
Author’s response to reviewer Dr Eleni Tracada
The intention of the author(s) to focus on the impact of the digital navigation to the road users’ behaviour is clear throughout this article. It is commendable that the environmental and social impact are also discussed at several points briefly. The article refers to important points that we have to consider before planning routes for road users, and it is good to consider the impact of individual choices to increased traffic in cities as well as in rural areas. In both cases, behaviours could be highly damaging to both humans and nature.
Although we can see references to several relevant sources, the authors say that there is lack of literature on the performance of digital navigation. Perhaps this is due to the lack of a meaningful interface to evaluate road users’ choices constantly via specific navigation systems, so that the road authorities should be able to make informed decisions on their strategies, too. In this case, feedback from research centres could have been asked constantly during ongoing national and international meetings, symposia, and conferences; more papers could have been published.
[Author response: I have been looking out for evidence of the impact of digital navigation in both the published research literature and the informal literature, but very little is to be found. I have used the TRID data base, to little effect, as the revised paper indicates. The road authorities seem not to be paying attention to changes in travel behaviour arising from digital navigation.]
However, we may have to consider the impact of the pandemic which had an impact on most commuters. So, there will be a gap of knowledge until commuting traffic or other solutions in mobility are back. But climate change has got an impact to lifestyles, too. So, many more disciplines may need to cooperate with digital navigation providers. In the future, road users may use a combination of virtual reality preparation before they experience the real journey. So ‘nudging’ could be an enjoyable gaming experience, if we think that smart traffic is more than estimated arrival time; that means stepping out of the car and experience an active healthy living environment integrating green infrastructure and human mobility in a variety of ways.
[AR: Indeed, these aspects are relevant to future travel behaviour, the subject of my forthcoming book: ‘Decarbonising Travel after the Pandemic’.]
It is good to see that high population density and car ownership in some cities may increase road traffic to both big traffic arteries and minor roads, when digital navigation refers to fastest routes especially. Therefore, it could be useful to show a couple of case study areas where this happens; it could be good to make recommendations at the end on how road users’ changes of behaviours in those areas not only could have a positive impact to them (physical and mental health), but also to their immediate surroundings. The paper flows well and shows clarity. Just few references related to examples of digital navigation in the light of autonomous vehicle (AV), driverless cars, could be useful; drivers and road users’ experiences could be very different soon, because freedom of choice could be almost prescribed to safeguard health and safety, and protect the environment, too.
[AR: Figure 2 of the paper is an example of a peri-urban area where digital navigation is likely to be changing traffic flows by offering routing options to local road users that minimise journey time. The impact of AVs on traffic congestion is beyond the scope of the present paper although I have discussed this previously https://www.mdpi.com/2413-8851/2/2/33]