[sustran] Bus lanes

[Kerry Wood]

I am in the middle of a paper on speeding up ALL traffic by making
public transport faster and more efficient. Here are some bits from it
(sorry, it has diagrams which get messy on e-mail)


ISTP data shows that cities with low car use have low overall transport
costs. (I have used their figures for operating cost of non-freight
transport)


For as long as the debate is about road building for cars, it is not so
much about improving transport as about how quickly it will get worse.


Huge figures for the cost of congestion are meaningless in a policy
context because there is no prospect of realising the savings: Mogridge
(1997) refers to ‘ghost city’ traffic flows. They can also be used to
support any option, and so cannot discriminate between options.


It has been known since the Buchanan report (1963) that full
motorisation is impracticable in a large city - especially if that city
has a high density.


Speeding up motor traffic is self-defeating in four ways:

-- If the car-carrying capacity of the road is increased, the cost curve
for cars is flattened. The result is that some passengers switch from
passenger transport to car use. More cars quickly offset the savings and
costs return to their old level (the cost curve is very steep in
congested traffic, so mode switching does not have to be on a large
scale). However, passenger transport costs increase because there are
fewer passengers: fares may rise, the operator may take off some
services, or the service may even close. Higher costs encourage more
passengers to switch to car use, so car costs rise until they reach the
new passenger transport costs. When the readjustments are complete the
point where the cost curves for passenger transport and cars cross is at
a higher cost than before the capacity increase: the road ‘improvement’
has increased costs for everybody.

-- Capacity increase in an urban area simply releases suppressed demand.
This accounts for the common observation, first made in the 1930s, that
a new urban highway does not reduce traffic on the old route (SACTRA
1994). SACTRA’s explanation is that new capacity induces new traffic on
an important scale, which is not allowed for in most transport
modelling.

-- Urban design effects. For example, good car mobility allows
supermarkets to drive local stores out of business, frustrating
accessibility and needing more mobility to meet the demand created

-- Buses are slowed down in four ways. They have greater difficulty in
re-entering a faster traffic stream after a stop, or in crossing fast
traffic to reach a right turn lane; they consistently miss traffic
lights set to give motor traffic a ‘green wave’ through several
junctions, because of the need to stop for passengers; they suffer long
delays at traffic lights set to maximise traffic capacity by using long
phases; and they often follow a more circuitous route to pick up
passengers.


Suppressed demand is usually a smaller economic problem than excess
demand. SACTRA (1999) studied the economic impacts of reducing traffic,
and concluded:

“The external costs arising from road transport provide a rationale for
traffic reduction insofar as it arises from the alignment of marginal
benefit with marginal social cost.  (7.125)

“..a more efficient allocation of resources might result from
well?targeted reduction measures. There is a strong case for correcting
market failure since marginal social costs appear to exceed marginal
benefit on many journeys.” (7.126)


Reducing capacity also has little effect on speeds. Cairns and her
co-workers (1998) found 47 traffic reduction schemes where usable data
was available, with an average area-wide reduction of 25% of the
capacity of the altered streets. Crucially, they could not find any
example of capacity reduction causing ‘traffic chaos,’ beyond a short
adjustment period (it will be alright by Friday), even when there were
catastrophic reductions due to earthquakes.


Road building making the situation worse is called the Downs-Thomson
effect. Thomson (1977) describes the process like this:

“If the decision to use public or private transport is left to the free
choice of the individual commuter, an equilibrium will be reached in
which the overall attractiveness of the two systems is about equal,
because if one is faster, cheaper and more agreeable than the other
there will be a shift of passengers to it, rendering it more crowded
while the other becomes less so, until a position is reached where
no?one on either system thinks there is any advantage in changing to the
other...

“Hence we derive one of the golden rules of urban transport: the quality
of peak?hour travel by car tends to equal that of public transport.”


Studies of door-to-door travel speeds in several cities show that speeds
on public and private transport are remarkably similar, and studies of
household travel surveys show that about 15% of commuter cars are not
used every day: there is mode switching going on.


Zurich is one of several European cities that have pursued a policy of
improving public transport for some years. It is a particularly
interesting example because excellent results have been achieved at
comparatively low cost, with few subways and some surprisingly old
vehicles. The head of VBZ, the Zurich transport authority, claims:

“The only way to reduce traffic problems is to promote public transport
.

“Our strategy has been promoting public transport, reducing
non-essential car traffic, funneling traffic onto trunk roads, reducing
parking provision and encouraging pedestrians and cyclists.”  (Heierli
1996)


Cost/modal split diagrams (following Mogridge) show that speeding up
passenger transport also speeds up cars EVEN IF SPACE IS TAKEN FROM CARS
TO MAKE ROOM FOR PASSENGER TRANSPORT. This is what has been done in
Zurich, as well as many other European cities. It seems to boost rather
than depress the economy.


ISTP data includes in-vehicle speeds for private and passenger transport
for a range of cities, as well as the proportion of journeys to work by
car. Plotting these gives a clear boundary line, which seems to
represent the Downs-Thomson effect: all the cities quoted by Mogridge
are on on close to this line.


Mogridge (1997) mentions sample calculations suggesting that in central
London average traffic speeds could be doubled by favouring passenger
transport: clearly this would being major commercial benefits. Trucks
have to be considered, but they do not necessarily need more road space
- they are usually only about 10% of a traffic stream.


A common assumption is that business people need car access, but what
they really need is good access. Heierli (1996) says:

“Zurich has... succeeded in giving its public transport operators the
image of modern companies with a clear customer focus, which... results
in a very positive image. The outcome of this is that there is no stigma
attached to travelling by tram in Zurich; indeed, anyone who does not
use the tram tends to be regarded as out of touch.

“Our politicians make regular use of public transport (not just at
election times) and leading figures from economic and academic life
would not consider commuting in any other way.”





References

Buchanan, C (1963)  Traffic in Towns. London: HMSO
Cairns, S; Hass?Klau, C and Goodwin, P (1998)
 Traffic impact of highway capacity reductions: assessment of the
evidence. London: Landor.
Heierli, R (1996)  European Lecture: Public transport in Zurich.  Proc
Instn Civil Engineers, Transport 117, November
Mogridge, MJH (1997) The self?defeating nature of urban road capacity
policy. Transport Policy 4 (1) pp 5?23
Thomson, JM (1977) Great cities and their traffic. London: Gollancz.
Quoted in Mogridge (1997)




I like the idea of running bus lanes in the ‘wrong’ direction to keep
cars out of the lane. Thanks Lake.

Another approach is to raise bus lanes about 80-120 mm above the general
traffic lanes (or about 150 mm with a beveled kerb), so that motor
vehicles can use them at low speed in emergency, but not just to save a
few seconds. Brussels uses a thing like a painted broken line, but the
‘paint’ is concrete and 100 mm high.

A good design for a ‘bus gate’ to keep other traffic out of a bus lane
is a narrow section of road, between kerbs, with a level surface where
the bus wheels go but a dip where the narrower car wheels go. It doesn’t
matter if the inner wheels on the back axle of the bus are unsupported.
The dip can be enough to slow cars down, or deep enough to stop them,
and a ridge (low enough to clear the bus differential) stops them from
going over the dip too fast for their wheels to drop in. The trouble is
that it is comparatively expensive, because the dip needs separate
drainage.



--
Kerry Wood  MICE  MIPENZ  MCIT
Transport Consultant
1 McFarlane Street, Wellington 6001, New Zealand
Phone + 64  4  971 5549