How to change things; could it be magic?

So, the discussion continues at Stoat about how to produce effective policy which balances present and future economic needs and benefits with emissions control.
So, like you do, I go on a trawl which gets diverted and before you know it I'm reading a neat new paper, Johannson et. al., at Atmospheric Chemistry and Physics:


The evolution of shipping emissions and the costs of regulation changes in the northern EU area
L. Johansson, J.-P. Jalkanen, J. Kalli, and J. Kukkonen
Atmos. Chem. Phys., 13, 11375-11389, 2013

in which the authors offer: "An extensive inventory of marine exhaust emissions is presented in the northern European emission control area (ECA) in 2009 and 2011..." Browse the paper, rather than the abstract: it's twenty minutes well spent.

So why mention it? The paper is interesting in itself for some of its details, such as that CO2 emissions from shipping in this area alone amount to around 500MT a year. But what makes it interesting in the context of this discussion is that it reviews the impact of specific regulation (in 2007) on emissions of Sulphur Dioxide, and relates certain connections between the costs, benefits and impact of the regulation.

First, in the period measured, SO2 emissions from shipping were better than halved. Second, the cost of this is estimated at about +10%. Third, the further introduction of retrofitted sulphur scrubbers would produce reductions proportionally larger than the comparable costs. (I think all of this is right...)

One of the conclusions of the paper is that slowing down cargo vessels by only 10% would result in even more SO2 (and CO2) reductions and save the shippers money. The paper does point out that it doesn't factor in the possible need to increase fleet sizes/movements to compensate for the extended travel times, but there is still a point here.

What would be the effect of reducing the National Speed Limit of road traffic (particularly haulage vehicles, but also personal vehicles) by a similar 10%? How much less fuel would be used? What cost savings would there be, and how much compensating increase of traffic would be needed?
Two points from this: the paper seems to indicate that the regulation of sulphur emissions over the past several years has resulted in considerable real reductions, at some cost (which does not appear to have restricted trade) to the emitters, for the benefit of all. Part of this no doubt is due to the fact that Maritime regulators have huge amounts of power (yes, they can shut down a fleet), so their rules are not ignored lightly. So; well-designed and enforceable regulation can produce results which, on the surface, represent a net benefit, not just for the regulated, but also for the affected.

The second point is that, following a similar logic, regulating behaviour by means of processes such as speed limits, or improving the design efficiency of diesel engines (see also the incredible improvements in Rail diesel systems over the past ten years), can produce the right kind of result without excessive constraints on either liberty or markets. It also means that (value chain ignored) the emitter is paying what cost there is.

Anyone got an opinion on this thought?