Martin J.H. Mogridge, "Travel in Towns", chapter 10

7/31/2019 Martin J.H. Mogridge, "Travel in Towns", chapter 10

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10 RoadBuilding

Some fallacies

Those who argue that roads must be improved in London seem to

fall very easily into a number of traps or fallacies.

i) London is grinding to a halt

This is a very old argument. Essentially, people who use thisargument take a limited time series of the traffic speed data. Theystart in 1974-76 when the traffic speed was unusually high becauseof the petrol price rise, and difficulty of obtaining petrol. Theyfinish in 1983-86 when the traffic speed was unusually low,possibly because the increase in demand for travel to the central areahad so increased the load on the public transport system that the

running speed of the trains had reduced owing to congestion atstations; thus, through the equilibrium process, the traffic speed onthe roads was reduced.

A regression equation through this limited data on traffic speedthus appears to show that speed is slowing down, and that byextrapolation it will be even slower in future. A value of7 miles/h by2000 is often quoted.

The regression of the morning peak speeds from 1974-86 gives:

traffic speed = 14.15 -0.59t

(where t = 0 in 1974, and in 3 years units) This gives a traffic speedof seven miles/h in 2010. The argument is that roads must beimproved to prevent this slow-down.

This argument is fallacious because it does not take a sufficientlylong time span of data into account. One might as well argue thatfrom 1962 to 1974 (the same timespan) the data showed that roadspeeds were increasing.

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ii) London road speeds are constant; as traffic isincreasing we must build more roads otherwise roadspeeds will fall in future

In its modern form this argument has been put most clearly by theWheels forChange pamphlet of the Movement for London, December 1987. The argument used to be used entirely in the central area,but now that it has been realized that the North Circular Road all-day traffic speeds have been constant for 50 years it is being usedmuch more widely. A recent example was the letter to the Times on

4 June 1988 by the Chairman of the Confederation of BritishIndustry, John Banham.

The argument is essentially that car ownership has grown substantiallyin fact in the 50 years from 1936 to 1986 it has grownnationally from about 1.8 million cars to about 18 million carsandthat it will continue to grow fast. Current growth rates are about

5 percent per annum. Moreover, the amount of freight to be movedby road is also growing fast. National surveys show that the averagetotal distance travelled by each car per year is fairly constant at

about 8,700 miles, so logically it would seem to follow that we needmore road space to prevent a slow-down in traffic speeds.

This argument ignores the fact that the increase in road space inLondon has not kept pace with the increase in car ownership in thepast. To take the specific example of the North Circular Road, it iscertainly not 10 times as big in capacity as it was in 1936. Why,then, have road speeds not fallen already, and substantially, given

the sensitivity of speed to flow in congested conditions?The simple reason is that cars based in London do not travelentirely in the London area. To take perhaps an extreme example,the car I share with my wife was used for about 1,000 miles last year,almost all of which was done outside the London areaor on directroutes in or out of the London area since we live in the centre.

The vast majority of car trips in London are of relatively shortlength, short duration and slow speed. The increase in traffic by

these cars takes place outside the London area.It can also be argued that there is a degree of peak-spreading (i.e.

that more travel is now taking place outside the peak hours) but itmust be remembered that the speed surveys on the North CircularRoad are all-day averages. Even if more travel is outside the peak


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Figure 10.1 Traffic flows on the M40 and adjacent corridors

hours, it is still travelling at a relatively slow speed; the peak speedson the North Circular are 19 miles/h, the same as the average speedin the whole area in which the road lies; whereas the evening off-peak speed is 28 miles/h, only about 50 percent higher.

Thus the vast increase in car ownership over the last 50 years hasnot led to a reduction in the all-day average speeds on roads such as

the North Circular, so there seems to be no reason to suppose that itwill do so in the future as car ownership continues to grow. It seemsto be quite absurd to claim that road engineers have just builtexactly the amount of road space required to keep speeds constant,since the amount of road space built bears no relation to the increasein car ownership. Moreover, in cases where road space has beenreduced for cars, such as the conversion of Oxford Street to a busand taxi-only road in 1972, there has been no diminution of the

average speed of road traffic in the surrounding area; although therewere indeed horrendous jams whilst the system settled down to anew equilibrium, over a period of about six weeks.

Even more telling, in cases where a substantial increase ofcapacity has been provided, it can be demonstrated that an increase


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278 Travel in Towns

iv) Even if traffic speeds remain unaltered by improvingthe roads, we must do it because people prefer to usetheir cars rather than travel on public transport

In the same letter quoted above from Olaf Lambert, he finishes withthe assertion:

'We can create a better transport system for London, but itmust accommodate the Londoners' wish to own and use carsin the same way as that right is enjoyed throughout the rest ofthe country.'

I have shown above that the use of the car in London, while atslightly lower speeds on average than in the rest of the country, isnot so dissimilar as many people seem to believe. The fundamentalpoint that Olaf Lambert is making, however, is that once a car ispurchased the owner is entitled to be able to use it.

I have no wish to discourage the ownership ofcars, and indeed inmy own work have forecast much higher levels of car ownership

than the government are presently contemplating (Mogridge, 1989).It seems to me, however, to be quite absurd to spend enormousamounts of money on road construction if all that is achieved is thesame journey speed as before, and to run the risk ofa lower journeyspeed if public transport services are reduced, when for the sameamount of money spent on investing in public transport one canachieve a speeding up of both the public transport system and the

private car, for those who still choose to use it.The individual cannot choose by himselfa better public transportsystem; that can only be done through government decision. But itis absurd to claim that because the individual can choose to buy aparticular car, then the government must provide him with thewherewithal to travel at high speed in it.

It is often argued that, because the individual has paid a great dealof tax in purchasing and using the car, the individual has a right to

expect the government to spend that tax money on the roads. Thisargument, that of hypothecation, is peculiar to roads and is notused, for example, to justify expenditure on pubs for alcoholconsumers, or smoking rooms for smokers, or sound rooms for hi-fiaddicts, all of which are highly taxed.


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The responsibility of government is to allocate the resources ofsociety in such a way as to maximize the welfare of the people, and ifpublic transport investment is the efficient way to do that then that

is the way that resources must be spent, even if those resources

come in part from tax on the private car.After all, what the individual wants is mobility, travel at higher

speed in comfort and security. It is the stated duty of government to

provide that. It cannot be done in London by improving the roads.It can only be done by improving the public transport system.Therefore, we have to design the public transport system to provide

the maximum increase in journey speed for the amount of resourcesavailable.

v) Congestion costs Londoners 1.5 billion per year;therefore more roads must be built to relieve congestion

This argument goes back a very long way, as already noted above.

In the latest pamphlet from the British Road Federation, (The Cost

of Congestion; June 1988), the details of their calculations are givenas follows. The costs of congestion are measured from the difference

in journey time under 'ideal' conditions and in reality, multiplied bysome value of time, plus the additional vehicle costs of travellingslower. The definition of 'ideal' condition is therefore crucial to the

argument.

The definition chosen is that condition where the driver is

unimpeded by any other driver, in effect where he is travellingin the conditions of the dead of night (say at 3 am), where thereis no other traffic to speak of. One can call these 'Ghost town'conditions. In the centre of the city, the speed assumed for these

ghost town conditions is 37.65 km/h (23.38 in innerLondon 42.48 (26.38 and in outer London 54.70(33.96 The values of the free-flow speeds are taken from

Glaister (1982). These speeds are approximately twice the speeds

actually achieved (quoted as 19.35, 19.36 and 32.16 km/h respectively for 1985/86), so the congestion cost is therefore approximately

half of what people spend on road travel.

These speeds actually achieved are, however, not the speeds

actually achieved but the BRF's estimate of what the speeds would


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280 Travel in Towns

be in 1985/86, based on the speeds in 1980/81, applying a growthfactor of of vehicles licensed' to the intervening years fromGLC-wide data and using the speed-flow relation given by Glaisterto estimate speed. These estimates of speed may be compared with

the actual speeds in as given above, and repeated here forconvenience. (I have used a simple weighting of 3:6:3 for themorning peak: midday off-peak: evening peak, rather than flowweighting.)

estimate

86/8actual

80/2

Central 12.02 11.1 11.8 11.9

Inner 12.03 12.3 14.1 14.9

Outer 19.98 20.2 20.4

It can be seen that the BRF method has substantially under

estimated inner London speeds in 1983/85 though the later speedshave fallen slightly. Curiously, however, given the method it has notmarkedly underestimated the central and outer London speeds,which have not changed appreciably in the period. Obviously onemust re-examine data.

The actual BRF method, whereby future speeds are estimatedusing growth factor methods on vehicle licences and speed-flow

relationships, will overestimate the costs of congestion because itwill underestimate speeds. Speeds are not set in this way by a speed-flow relation when demand is suppressed; they are set by theequilibrium with public transport journey speeds.

There are indeed people for whom the ideal conditions would beif everyone could travel at the speed they could on an unimpeded

at 70 for the majority of theirand only at the ends of their journey travel at the local speed.

As we have seen in Chapter Nine, the vast majority of journeys bycar are actually very short, and certainly comparable in lengthto the distance between intersections on a motorway operating at 70

miles/h. The vast majority of trips could therefore never be on amotorway network, but would always be on a local network.


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Implied therefore in these definitions of 'ideal' conditions is that itis possible to build a road network on which everyone can travel as ifthere were no other driver also travelling at the same time. These arepatently absurd conditions because the problem of urban travel is

that we do all want to travel to the same location at the same time.It is in the very nature ofa city that that should be so, at least in ourpresent culture where face-to-face contact is all-important.

The cost of congestion is therefore an invalid concept in an urbanarea like London. What we need to do is to consider what are theways available to speed up movement, and how much it costs to doso; not to attempt to define an condition which is impossibleto achieve.

We cannot reduce congestion by building more roads sinceimmediately we get more traffic to fill them up to the same speed asbefore. The only way to reduce speed upto introduce better public transport facilities which reduce thenumber of people who travel by car on the roads.

Documents

Martin J.H. Mogridge, "Travel in Towns", chapter 10