One thing that is absolutely clear in the battle against congestion and pollution is that modal shift away from the private car is essential.
The fundamental issue is space-efficiency. Cars are horrendously inefficient users of the precious limited space available in urban environments. It doesn't really matter what alternative mode is used - whether walking, cycling, bus, tram, or train - changing the mode is always a big win. No, self driving cars don't help, and may make matters worse. Electric cars don't help either, you still have to get the power from somewhere, and they still have significant particulate emissions.
For larger cities, trams or rail are key. There's still work to do to drive the cost down in smaller towns and cities, but things running on rail solve the particulate emissions problem. The problem is that, while efficient, they provide more transport capacity than smaller conurbations can take advantage of. In addition, it takes years to develop a rail network.
Which leaves buses. Not ideal in the long term, but available right now. How do we get people to move onto buses - and drive up ridership on public transport to justify investment in better solutions?
What about making public transport free? After all, Luxembourg has done it. Clearly adds to the attractiveness, but can we afford it?
Consider Cambridge. The city has a population of about 125,000; with the surrounding area we might consider a quarter of a million people are in scope.
Giving that many people free public transport will cost a fortune, and we can't possible afford it. Correct?
Not so fast. The MegaRider ticket is £15 for 7 days travel. Let's round that and say it's £2 per person per day. That's a charge at which the current bus service is profitable.
What's a reasonable estimate of the number of users? Not the whole quarter of a million. Pensioners already have bus passes. Some walk, some cycle, some are already close enough to a railway station. Some, for work purposes or for special needs, will be unable to use public transport. Let's say we're targetting 100,000 people 5 days a week. That's £1million a week, or £50 million a year.
OK, that's a fair amount of money to you or me. But the CAM project (Cambridge Autonomous Metro) is talking about an eye-watering cost that may reach £4billion. Instead of funding CAM, we could fund free bus travel for everyone in Cambridge for 80 years. The Greater Cambridge Partnership was talking about a £1billion investment for the City Deal. The recent A14 "upgrade" was over £1billion.
In those terms - and in terms of many of the other projects being proposed - funding free bus travel is a bargain.
We're not done yet.
Increased ridership means fuller buses, so utilization goes up. So the cost per journey goes down.
Increased ridership justifies a denser mesh with more routes, leading to greater efficiency, driving down unit costs.
Modal shift reduces congestion, cutting journey times, so you don't need as many vehicles or as many drivers to provide the same service, driving down costs even further.
Not charging means a massive reduction in boarding times, which as I've talked about before is a major contributor to delays and inefficiency.
It's not hard, within the city, to see journey times cut in half through this process. And maybe utilization can almost double. Which means that the actual cost goes from £50million a year to £20million a year. The CAM could fund that for 2 centuries.
And that's the fundamental thing. Pretty much every single transport project currently being floated costs more - often many times more - than simply making buses free. There's a downside here - providing free buses may be sufficiently successful in the short term that it could kill off the prospects for the better long term projects. But it gives us the breathing space to develop the better solutions without destroying our cities and the planet in the meantime.
And that's only covered the direct costs, ignoring the indirect benefits such as: reduced journey times and increased productivity; decreased pollution and better health giving savings for the NHS; cleaer street and a better public realm; and so on.
Perhaps we should be asking not whether we can afford to do this, but whether we can afford not to.