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A low-carbon transport system for heavy vehicles
Heavier road vehicles are responsible for approximately 40% of UK domestic transport CO2 emissions.
vehicles are usually powered by Diesel engines, which substantially contribute to local environmental problems
such as poor air quality in the form of particulate emissions and annoying low frequency noise. They also pose
dangers for the occupants of smaller vehicles and pedestrians by compromising their safety thereby
discouraging environmental improvements.   In theory, a large proportion of road based transport operations
could be transferred to the rail infrastructure to overcome these problems, however this is not the mode of
choice for most travellers and freight operators.  In this section we discuss how the rail infrastructure could be
adapted to meet the requirements of modern freight movements and travellers whilst meeting acceptable
environmental objectives.
Advantages and Limitations of rail transport
Passengers and freight operators rarely require transport between stations or railheads, but residential districts
and businesses. The demise of large industries and concentrations of population away from town and city
centres have exacerbated this effect.  Hence rail in isolation can rarely meet modern transport requirements
without an intermediary transfer to another vehicle. These diversions and transfers lengthen the overall
journey, much of which has to be driven on the road which increases the critical ‘door to door’ time.
Another limitation of rail is that transport capacity along a given length of railway network is often much less
than the equivalent length of road highway especially in populated regions. This is partly due to the limited
friction between the metal wheels and rails of the locomotives and carriages.  This necessitates long distances
between successive train units so they can brake in time to avoid collisions or derailment at switches or points
where lines meet and diverge at junctions. As a consequence, some rail systems are already at capacity at peak
periods on congested networks. Conversely, at non-peak times and in less populated regions the rail
network is chronically underused, necessitating large subsidies to maintain the infrastructure and fund
underutilised trains.
One advantage of railed transport is that it allows the towing of multiple passenger carriages or freight wagons
or ‘trains’. This obviates some of the capacity disadvantages and reduces aerodynamic resistance. In conjunction
with the reduced rolling resistance as a result of using steel tyres, trains generally have superior fuel efficiency
per tonne carried relative to road vehicles.  However, this comes at the cost of flexibility since the longer the
train, the longer is the interval between successive trains for a given overall capacity. For passenger trains this
increases the waiting time at stations and the effective (door to door) journey time for the passengers. This in
turn reduces the attractiveness of using rail in preference to private transport, leading to poor utilisation and fuel
consumption per passenger, since a minimum number of trains must be supplied to maintain a basic service. The
benefits of using rail for freight transport are similarly compromised by having to transport bulk loads. There are
substantial economic benefits for a modern business in maintaining low stock levels with low warehouse space
requirements. However, this requires large numbers of small deliveries, which are far more suited to trucks
rather than rail transport.
A number of studies have questioned the environmental benefits of rail, drawing attention to the low average
passenger utilisation and heavy weights of modern railway carriages.
55 56 57
   Some of these suggest that rail has
a greater energy use per passenger km than the equivalent bus, coach or even car journey for many practical
situations.  It also appears that rail is not significantly more energy efficient than large HGVs for many types of
multimodal freight operations.
This may be due to energy losses incurred during travelling to the rail terminal
by truck, shunting rail wagons into position, and the heavier wagons used to withstand the forces used in a long
54 Buses, HGVs, LGVs & Rail combined relative to total domestic transport emissions, table 3.7 Carbon dioxide emissions in the United
Transport (2001)
56 Rail Loses the environmental advantage, June 2004, Modern Railways, Cars More Energy Efficient Than Trains?  Some web
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