Travel should go through this decision tree:
- do we need to travel, if not then don't. (e.g. should I be looking to WFH more of I'm able or do I really need to go to the shops today and tomorrow?)
- if we need to travel is it suitable to walk it & if its not could there be something I could change to make it so that it was?
- if not could we cycle it & if its not could there be something I could change to make it so that it was?
- if not could we use public transport & if its not could there be something I could change to make it so that it was?
(By this point in the tree it should be theoretically possible that we've covered most of the travel carried out by most of the people).
- if none of those modes are practicable, could I share a vehicle with others to reduce the numbers of vehicles on the roads?
- then and only then drive
The problem is that rarely do we, as a nation, run through the questions and we often just jump in the car as we are lazy in our thinking as well as being fairly lazy in our actions.
For instance, do you really need to drive to a supermarket to get an extra pint or two of milk? Yes the cost is the milk is cheaper, but if you didn't drive a mile there and back (saving ~20p) it might be cheaper to walk to the local shop/garage and pay the higher price on the milk. Even if it's not cheaper, there's probably not much in it, which wouldn't be that big a deal for small top up shopping which should be fairly infrequent.
Now whilst there'll be some who wouldn't be able to walk/cycle/use public transport for the majority of their travel (especially if they can increase the amount that they WFH) rather than drive, a lot of them will be within groups which make up small percentages of the population.
For instance, those with disabilities (and many still can, for example hand cycles, mobility scooters, etc.) make up about 6%, those classed as living in a rural settlement (government definition of a population of less than 10,000; even then I do in a village of 9,000 and I've got the option of an hourly bus and a twice hourly train service) make up ~15% of the population.
Now I accept that is simplistic, in that you can't get to everywhere within a reasonable timeframe (for instance my wife's work would take 2 hours to get to by public transport) and the change needed to make that viable by public transport would be to move (then the problem is that closer houses would be much more expensive and would mean that I then couldn't walk/cycle to work).
However, by WFH an average of 1 day a week (she only works 3 days a week anyway) and limiting as much of our other travel to walking/cycling as possible, we only own one car and the miles we do in that are below average (average per car is ~10,000 miles, average per person is 6,500 miles).
If my wife changed jobs, so could walk, cycle or use public transport, then we would probably not really need to own a car (although would still need to hire a car for visiting family).
Often there's one or two main journeys which are why people keep a car. Given the ability to have supermarket deliveries for the big and heavy stuff (which gets delivered to at least your front door, so less heavy lifting than going and getting it yourself) then even that 1990's justification for car ownership isn't as strong as it used to be.
Yes there's some journeys which you can't do, for instance going to the household waste centre, without a vehicle. However, how often do you really do that trip (I've not been for the whole of 2020 and I've taken all the tiles off my bathroom walls, we just put a some in the bin each week)? Chances are you could get rid of most stuff in another way if you needed to.
Coming onto the main subject of the thread, having a OHLE/Diesel/Battery train is going to be, for the vast majority who use it, more environmentally friendly than nearly any alternative mode of travel that they could use instead of using it (nearly any, as EV's may win out if it's a daily trip with multiple people in the vehicle, likewise a very short trip which could otherwise be cycled wouldn't be better by train).
Yes there's a risk that electrification is delayed on the route, however there's still going to be a need for a lot more than there currently is before the gaps are short enough not to need the diesel engines. Even then chances are the case for shortening those gaps more would likely be fairly high.
What it may well allow is a faster roll out of electrification, in that it could be possible to have the wires up but they don't quite have enough grid feeds to run all the trains without help.
I'll give you an example, Weymouth, that's limited on the number of EMU's which can be running at any one time, if we had trains with a battery boost then chances are you could run more trains.
Now if we can reduce the number of grid feeds on some of our more rural lines then it could allow them to have the wires installed more cheaply than would otherwise be the case. It could also allow them to be added in at a later date, so that the delivery of grid feeds want such a time critical element of the project (although given the amount of planning required to deliver electrification, that's likely to generally be less of an issue).
Yes batteries aren't great environmentally, but then it's better to build a few and put them in trains than thousands and put them in cars (even if the train battery is much bigger). Especially if they are only being used for parts of the journey being made by the train rather than all of way as it's the case with cars.
Such improvements should further reduce the need for so much diesel use within the railways, further improving the carbon emissions so that the average starts to beat (rather than the 2019 figures where they were broadly matching) the per person per km emissions of EV's (however that still smashes the average by road vehicles, even if you include emissions produced by cycles within those numbers).
It's likely, with everything (even with fairly limited electrification beyond what's already announced), that by 2030 rail should be able to be beating (as an average) EV's on emissions on a per person per mile basis.
Whilst there's likely to be still quite a lot of travel on diesel trains at that time, few using such services would actually be better off (in emission terms) from not using rail. As there's likely to be some travel that they do by rail which would be using electric (including battery) as the main power source, which would fairly rapidly reduce the per mile emissions. As well as the fact that they are more likely to walk/cycle the remainder of there travel than someone with a car, meaning that their overall travel emissions are likely to be lower overall.