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First principles assessment
Why
introduce urban traffic control systems?
Demand impacts
Short and long run demand responses
Supply impacts
Financing requirements
Expected impact on key policy objectives
Expected impact on problems
Expected winners and losers
Barriers to implementation
Why introduce urban traffic control systems?
UTC systems can be used to obtain better traffic performance from a road
network by reducing delays to vehicles and the number of times they have
to stop. UTC systems also can be used to balance capacity in a network,
to attract or deter traffic from particular routes or areas, to give priority
to specific categories of vehicles such as public transport or to arrange
for queuing to take place in suitable parts of the network.
The other potential benefits which can be obtained from the installation
of UTC systems include (IHT, 1997):
- improved facilities for pedestrians and cyclists;
- allocation of priority to emergency vehicles responding to incidents
and reducing vehicle attendance times, using special signal-timing plans
to favour key routes from fire and ambulance stations;
- implementation of diversion schemes to deal with emergencies or special
events and other control strategies such as tidal flow schemes;
- improved utilisation of car parks and a reduction in the amount of
circulating traffic by providing car park information systems;
- improved fault monitoring and maintenance of equipment, leading to
a reduction in the delays and potential safety hazards caused by faulty
equipment; and
- interaction with other network management systems such as a route
guidance system.
Demand impacts
UTC systems generally aim to produce the minimum total queue-length on
the network or the minimum total vehicle hours for a given amount of travel,
but reducing travel times and increasing capacity over a significant area
may cause a shift in demand towards car use. However, UTC systems may
also have the potential to reduce or limit congestion by analysing the
congestion and determining the critical part of the network that causes
a particular problem. As most systems also improve travel times for buses
to the same degree, or possibly further by giving priority to buses, the
overall effect on demand would seem to be neutral.
| Responses and situations |
| Response |
Reduction in road traffic
|
Expected in situations |
| 
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Increase in peak where reducing
travel times and increasing capacity may reduce congestion |
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Reduce overall where reliability
of selected roads improves by minimising total vehicle delays of
whole network |
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N/A |
| 
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Where reducing travel times
and increasing capacity may attract car users, and may induce re-routing
within the network |
| 
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Some increase where reducing
travel times and increasing capacity may attract car users, but
some decrease where priority for public transport improves reliability |
| 
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Some increase where reducing
travel times and increasing capacity may attract car users |
| 
|
|
N/A |
Short and long run demand responses
It is unlikely that there will be significant change in demand response
over time. However, increasing the supply through reduced travel times
may induce re-routing within the network and so erode possible benefits
in the signalised area in the longer term.
| Demand responses |
| Responses |
|
1st year |
2–4 years |
5 years |
10+ years |
|
|
- |
|
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- |
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Change job location |
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| |
Shop elsewhere |
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Compress working week |
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| |
Trip chain |
|
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Work from home |
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Shop from home |
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Ride share |
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|
- |
| |
Public transport |
|
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* |
| |
Walk/cycle |
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- |
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- |
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* This is likely to increase shift in the long run if reliability of
public transport becomes better than before.
Supply impacts
There will physically be no increase in the supply of road space, but
reduced travel times and good network performance may in practice increase
road capacity. When UTC systems accompany the introduction of physical
restrictions such as bus priorities and light
rail systems, the supply impacts will be greater by adjusting the
traffic signal setting between car use and public transport.
Financing requirements
UTC systems require some technological equipment such as central computer,
signal controllers and vehicle detectors in any type of system. In addition,
traffic responsive systems usually use inductive loop detectors, with
the expense of installing and maintaining. For example, TRANSYT costs
£10,000- £15,000 per junction and £20,000 - £25,000
for SCOOT (Source?). When UTC systems are implemented for specific objectives
(such as traffic restraint) on selected roads in the network, the design
of customised systems are required, and are usually expensive.
Expected impact on key policy objectives
UTC systems have potential to contribute to a number of key objectives
through reduction in congestion, but the scale of contribution is dependent
on the specific traffic management objectives.
| Contribution to objectives |
| Objective |
Scale of contribution |
Comment |
| 
|
|
By reducing delays, improving
reliability and prioritising selected vehicles |
| 
|
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By increasing community severance |
| 
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By reducing air pollution
|
| 
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By improving public transport
conditions |
| 
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If congestion is reduced sufficiently
to allow increased speed, but reduced stop/start usually reduces
accidents. |
| 
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By freeing up potentially
productive time currently involved in delays |
| 
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|
By installing and maintaining
technological equipment |
Expected impact on problems
UTC systems may increase car use, but may also reduce congestion. Hence
they have the potential to contribute to the alleviation of a number of
key problems.
| Contribution to alleviation
of key problems |
| Problem |
Scale of contribution |
Comment |
| Congestion-related delay |
|
By reducing delays to vehicles
and the number of times they have to stop |
| Congestion-related unreliability |
|
By reducing delays to vehicles
and the number of times they have to stop |
| Community severance |
|
If congestion is reduced sufficiently
to allow increased speed, severance may increase if there are no
mitigating measures. |
| Visual intrusion |
|
- |
| Lack of amenity |
|
- |
| Global warming |
|
By reducing stop/start conditions |
| Local air pollution |
|
By reducing stop/start conditions |
| Noise |
|
- |
| Reduction of green space |
|
- |
| Damage to environmentally
sensitive sites |
|
- |
| Poor accessibility for those
without a car and those with mobility impairments |
|
By enhancing the reliability
of public transport |
| Disproportionate disadvantaging
of particular social or geographic groups |
|
By enhancing the reliability
of public transport |
| Number, severity and risk
of accidents |
|
If congestion is reduced sufficiently
to allow increased speed, but reduced stop/start usually reduces
accidents. |
| Suppression of the potential
for economic activity in the area |
|
By improving the efficiency
of the local road network |
Expected winners and losers
If reducing delays to vehicles leads to reduction of congestion the benefits
will accrue to all road users. However, winners and losers will depend
on the traffic management objectives through UTC systems.
| Winners and losers |
| Group |
Scale of contribution |
Comment |
| Large scale freight and commercial
traffic |
|
Where reduced congestion is
achieved on routes or areas used by freight vehicles in UTC-based
traffic systems. |
| Small businesses |
|
Where reduced congestion and
improvement of pedestrian facilities encourages use of local amenities. |
| High income car-users |
|
May benefit from reduced congestion |
| People with a low income |
|
May benefit from reduced congestion |
| People with poor access to
public transport |
|
Reduced congestion will improve
public transport reliability, but not solve problems associated
with poor access for public transport users. |
| All existing public transport
users |
|
Priority for public transport
based on UTC systems, aimed to track buses through the network and
adjust the traffic signals, will improve public transport reliability. |
| People living adjacent to
the area target |
|
May benefit from reduced congestion
and pollution |
| People making high value,
important journeys |
|
Where these journeys such
as emergency vehicles will have higher values of time, so that they
may be selected as priority vehicles. |
| Average car users |
|
May benefit from reduced congestion |
Barriers to implementation
| Scale of barriers |
| Barrier |
Scale |
Comment |
| Legal |
|
There are no obvious legal
barriers to the introduction of UTC systems. |
| Finance |
|
Inductive loop detectors are
usually used in traffic responsive systems, but installing and maintaining
them subsequently are significant in the cost. |
| Political |
|
There are no obvious political
barriers to the introduction of UTC systems. |
| Feasibility |
|
Feasibility studies such as
cost benefit analysis and financial analysis are required to introduce
UTC systems. |
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