This note describes an idea to measure accurately the exact parameter we wish to measure to reduce traffic congestion. It can be used on any road over the whole country with no static ground equipment. It needs no information about vehicle position and makes no intrusions on civil liberties.
Each vehicle would carry a box with an electronic circuit containing a transmitter, a receiver and counting circuitry. Each unit would transmit a pulse of a few thousand cycles of a radio signal with a frequency of a few GHz at intervals of, say, three seconds. The amplitude of the pulses could vary in a controlled way with a progressive series of values. The power would be very low, just enough for the biggest pulses to be detected by receivers on other vehicles at perhaps 100 metres and the smallest pulses at about three metres. By chance a few of the pulses from nearby vehicles may be coincident but this is of no concern and all transmitters can use the same frequency thus minimising the use of the available bandwidth.
When a unit is not transmitting (most of the time) it would receive pulses from other vehicles. It would count the total number of pulses that are above a chosen threshold. The count rate would depend on how close a vehicle was to how many other vehicles and so would be an accurate indicator of local traffic density at that time. This is an exact measure of the anti-social behaviour of occupying space on a busy road which we want to discourage. It would operate with greatest effect at the most crowded places and the most crowded times of day.
Instead of paying a fixed cost for a Road Fund licence, the vehicle owner would, at convenient intervals such as a vehicle service or the annual MoT test, pay an amount based on the accumulated count perhaps with a multiplier for the vehicle type. The units can display the current total and the cost for any part of a journey so that drivers will get a strong message about the current cost of being on the road at that time and place. They can learn to avoid expensive times and places if they choose to do so.
From time to time the accumulated count must be read from the unit and the charge calculated. This could conveniently be done by equipment in a garage which is doing a vehicle service or MOT test and can add the congestion charge to the service invoice. In the UK garages already do a good deal of form-filling, VAT collection and measurement of parameters like exhaust emission. The congestion count download would be only a small addition. The actual charge would be based on the accumulated count since the last readout, perhaps with a multiplier for dirty engine type and vehicle size.
The fixed border and time charges have proved effective but unpopular at the discontinuities and cause great annoyance because of false charges. There are various reports about setup and running costs of the central London scheme. An initial setup cost of £200 million and running costs between £90m and £130m a year have been quoted with a net revenue of only £50 m.
Nearly one thousand people are needed to process one transaction a day for each vehicle and chase the defaulters. If we can make the pulse-counting boxes for £20 each, the initial capital investment for 25 million vehicles over the entire UK would be £500 million, little more than double that for central London alone. It would be spread over the whole vehicle life. Subsequent investment for 2.4 million new vehicles a year for the entire UK would be £48 million, less than half the running cost for central London. There would only be a few accounting transactions a year as opposed to one a day.
The low running costs of the scheme mean that a large fraction of the money raised will have to be distributed somewhere. An early criticism of the idea raised thorny arguments about where the money should go. The congestion dividend could go to people on the electoral roll who actually turned up to vote or filled in genuine papers for a postal vote. Each person would be given a claim certificate, the value of which would be determined when the total number of eligible people was known, soon after each election. Everyone would feel that they had won a small lottery. While voters would still have the right to abstain there would be a strong incentive, perhaps several hundred and maybe a few thousand pounds, to turn out. This would be most valuable for democracy as well as for traffic congestion and the redistribution of wealth. It would be very likely to be accepted by the majority of the population. It is fair because, through their lifetime, everyone has the same chance of being a voter. The only unfair aspect is that credit for the resulting post-election economic boom would be claimed by the winning political party.
If a small fraction of the community causes a large fraction of the congestion it follows that quite a large majority of the population, in particular the poorer sections, those from rural communities and non-drivers, will cause less than average congestion and so would get a net benefit at the expense of a few heavy, urban road users. Everyone would have an incentive to cause less than average congestion and would be competing to do exactly what is needed.
Steven Salter is Emeritus Professor of Engineering Design at the School of Engineering, University of Edinburgh