Review of 'The Impact of Digital Navigation on Travel Behaviour'

This is a very interesting paper. I have only a few minor comments which the author may wish to consider.

1. 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.
2. 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.
3. 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).
4. 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).
5. 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.
6. 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.
7. 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).
8. 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…”
9. 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.
10. The TfL ‘case study’ is revealing and quite dramatic!
11. Can the following phrase be safely deleted from the end of the sentence in which it sits: “as well as extending such local knowledge”?
12. 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?
13. 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?
14. The reader would like to know a little more precisely what Derrow-Pinion found.
15. Is it the case that ‘commonly older vehicles are tested annually’? I thought MOTs were every three years.
16. 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?
17. 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.