Cork-Screwed?

Often, when one sees something incredibly absurd - one struggles to find a logical explanation. "The Dartford Crossing" is one such infuriatingly-stupid example that should make both economists and motorists weep.

To being with, the UK, has few toll roads. Road license fees and petrol taxes ostensibly are meant to fund the upkeep and maintenance of highways.  Outside of the M6, and a handful of bridges/tunnels, there are no additional usage fees outside the taxes/fee mentioned. This is both good and bad. No tolls certainly speeds traffic. But it also provides a hidden subsidy lowering transport costs, suffers from the tragedy of the commons where every stray beer-can and plastic shopping finds its way to roadside, and there is little incentive to maintain roads which are potholed and it seem chronically underfunded and poorly-maintained. There are also fairness issues associated with this. The French, by contrast,  have gone the private route for their major arteries, which delivers a large network of amazingly smooth, quiet, clean, safe roads, with excellent technological investment and adoption to further speed the flow, albeit at eye-wateringly expensive prices of something like EUR10 per hundred km.  One need only take the A6 out of Paris from the Porte d-Orleans in order to experience the difference between the public and private management. And though there are the occasional "bouchon"  (cork=traffic jam), price DOES keep people (and HGVs) off the motorways, and there is choice with the N-roads or "Route National" adjacent to most motorways that remain free, though subject to congestion, and vagaries of local traffic. Switzerland takes a somewhat middle ground, adopting a peculiarly Swiss-style solution: the Vignette. This is a CHF45 annual decal one must affix to their windscreen if they wish to use the (generally clean, safe and well-kept) motorways. Excepting those crossing the border into Switzerland via a motorway who are forced to buy one by commercially-minded border guards, it relies on the honor system, with harsh penalties for rule-breakers. The result is a hybrid pay-by-use with the efficiency gains that result from eliminating toll booths and collection bottlenecks. Their alternatives are typically more limited by the geography of Switzerland, and in any event HGVs (trucks) are often forced to traverse the nation via the rail network, or take a large and long detour through France or Austria.  

Now, back to Dartford. The day I am sitting for half-an-hour in a tailback caused by toll-collection, I read an article extolling transport pricing's positive externalities.   In it, Krugman is thankful for a VoxEU piece quantifying the benefits of investment in public transport, and road pricing in causing people to switch to public transport. All well and good. Dartford's tolls were kept ostensibly as a means to use pricing to discourage use, as much as they were kept to generate revenue for a threadbare Treasury. But Dartford is the ONLY passage to the east of London (that is not a boat), and it is the most critical and vital link in the ring-road around London, and the only way for HGVs to get to and from the Channel Tunnel. There are no rail links or alternative routes. In effect, the supply curve is completely inelastic, and so too, are the demand curves. The only result from toll collection is the cause of massive negative externalities in the form of endless traffic jams, pollution, inefficient lost output and waiting time, and increased consumption of fossil fuel. There is are no redeeming qualities to the imposition of tolls (the infrastructure has been paid for and then some) other than pecuniary short-term gain to the Treasury at the expense of massive negative externalities. It makes you want to rip your hair out. Worse still given the inelastic demand and supply curves, they charge during the busiest times yet waive the charge when its empty, when, the public interest would be served by the opposite: making it free and zooming everyone through when its busy and charging when it's empty, and the negative externalities are greatly diminished.

Am I missing something? Analysis by more competent economists would be appreciated....