urban traffic control - An interactive ITS Handbook for Planning

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urban traffic control - An interactive ITS Handbook for Planning
URBAN TRAFFIC CONTROL
Index
Purpose
Description
Relevance for Large Scale Events
Options
Technologies
Impacts
Integration potential
Implementation
Best Cases and Examples
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Purpose
The primary purpose of Urban Traffic Control systems is to ensure traffic safety at intersections. Traffic
signals make it possible to reduce the risk of collisions between cross traffic or vehicles turning across the
opposite flow. Through the coordinated management of traffic signals, UTC systems are able to increase
the efficiency of traffic flows by allowing vehicles to pass through a succession of signals without needing to
stop. This reduces the incidence of queues at traffic signals as well as fuel consumption and hence,
indirectly, vehicle emissions.
UTC systems which operate over a wide area can be used to balance capacity across the road network,
minimizing the overall delays to traffic and decreasing trip time. When integrated with fleet management
systems they can also be used strategically to give priority to specific categories of vehicles such as public
transport and emergency vehicles.
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Description
The main elements of a UTC system are the traffic signals installed at intersections, which are connected to
local control units installed on the roadside. These are connected in turn to the sensors used for traffic
detection and to a central management system. The objective of the system is to manage traffic at
intersections in such a way that safety is guaranteed and the buildup of queues and overall waiting time is
minimized. At a higher level, the aim is to optimize the traffic distribution across the whole of the
controlled network.
The co-ordination of signals between adjacent traffic signals involves designing a plan based on the
duration of individual signals and the time offsets between them. The signals therefore need to be linked
electronically and also connected with a central system (except in the case of isolated junctions).
The approach to the coordination of the signals has evolved from the ‘fixed time’ systems used in the
1960s, which develop timing plans based on off-line analyses of traffic patterns, to sophisticated real-time
traffic adaptive systems which modify the traffic phases to meet current and forecast conditions on the
road network. Traffic responsive systems calculate the traffic signal settings (cycles, green splits and
offsets) in such a way that they optimize a given ‘objective function’, such as the number of stops or the
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overall travel time. This is calculated in real-time on the basis of estimates of traffic flows, derived from
historical data, measurements of current traffic conditions, and other relevant events.
UTC systems can be interfaced with public transport management system making it possible to give priority
at intersection to buses and trams, and also emergence vehicles.
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Relevance for Large Scale Events
Since the free flow of traffic and the avoidance of congestion will be one of the principal aims of the
transport strategies for large events, UTC systems can potentially play an important role, in combination
with other forms of traffic management.
One of the features of all large events is the occurrence of abnormal traffic (i.e. intense flows on routes or
at times not normally subject to heavy traffic). Events such as the Olympic Games and World Cup, for
example, will generate exceedingly heavy traffic flows to/from venues at the start/end of events or
ceremonies. Unless underground transport systems play a major role in transporting passengers, the result
is likely to be serious road congestion at critical parts of the network.
The host city will almost certainly already have an UTC system, so it will be necessary to decide what kind of
adaptations or extensions are required in order to enable it to deal with the additional traffic, and how to
implement them. If the area affected by the event does not have an existing UTC system, the transport
organizers must set up whether one is justified, which intersections should be equipped, and what kind of
system to install.
A fixed plan UTC will not, by definition, be suitable for regulating the unpredictable traffic typical of large
events. The type of traffic control system most likely to be useful for host cities are:
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real-time traffic-adaptive UTC systems at intersections most affected by unpredictable traffic flows
(near venues or on key routes, e.g. between the airport and the city);
‘green wave’ systems for long axes where traffic flow may be heavy in some periods or in one
direction;
systems able to give priority to public transport (in host cities where there is expected to be heavy
use of buses or trams);
UTC systems able to give priority to emergency vehicles;
UTC systems which take into account pedestrian flows (e.g. provide an adaptable phase for
pedestrians).
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Options
UTC can be used for single (isolated) intersections, for major axes, or for a more extensive part of the road
network. Different types of strategy may be implemented, but the main distinction is between the fixed
time/plan selection approach and traffic adaptive systems.
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Fixed time control
Traffic signal timings are calculated off-line using traffic flow data collected by surveys. The timings are
based on average flows and a series of signal plans implemented (different plans are generally used for
different times of day, e.g. morning peak, off-peak, evening peak). As traffic grows and travel patterns
change, every few years new signal plans will need to be calculated. Fixed time control systems do not
respond dynamically and therefore cannot cope well with incidents, such as accidents, or unusual traffic
flows, e.g. generated by large events. The result will be congestion and loss of capacity in the network.
(Systems of this kind include TRANSYT, used in the UK since the 1960s).
Plan selection systems
These systems select the appropriate traffic control plan on the basis of information received from the
traffic detectors placed strategically across the road network. When a particular traffic pattern is identified,
the system automatically implements the relative plan. Such systems may also adjust according to weather
conditions (e.g. dry and wet conditions) and other factors likely to affect traffic patterns (e.g. school days
and holidays). They can in some cases be adjusted to run a specific plan for special events, e.g. football
matches, but otherwise have similar advantages and disadvantages as fixed time systems.
(Systems of this kind include SCATS developed in Australia the 1980s and used in numerous countries
worldwide).
Traffic responsive UTC
These systems are ‘dynamic’ in the sense that they respond automatically to changes in traffic demand and
are therefore better able to cope with unexpected incidents. The adjustment time will depend on the
specific system, but maybe as frequent as every few seconds. They can be divided into two main types:

Centralized traffic responsive systems
Such systems make use of a central computer which receives data from the network, calculates the control
plan in accordance with the high level strategy, and communicates this to the individual traffic controllers.
A centralized system has the advantage that all the relevant information, from the detectors and other
sources is available in the same place.
(Systems of this kind include SCOOT widely used in the UK)

Distributed traffic responsive systems
The main characteristic of distributed systems is that the local controllers (located at the intersections)
have greater autonomy or ‘intelligence’. Although the overall strategy is provided by the central level, each
controller is connected to the neighbouring controllers and messages are passed between them so that
forecasts can be made of the ‘platoons’ of vehicles due to arrive at successive intersections. Local coordination is achieved by linking controllers by dedicated cable or cableless links between microprocessorbased controllers. The advantages of distributed systems are similar to those of centralized UTC, but have
the added advantage of permitting faster adaptation to real traffic conditions and facilitating the
management of priority for public transport vehicles.
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(Systems of this kind include UTOPIA-SPOT developed in Italy, and PRODYN, France)
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Technologies
The main components of a UTC system are:
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Central system
Communication Network
Roadside Units
Traffic signals
Traffic detectors
User Terminal
Application Server
LAN
User Terminal
Central System
Communication Server
Communication network
MFO
MFO
MFO
MFO
The hierarchical structure of a demand responsive UTC system
UTOPIA for example has a two-level distributed architecture. The upper level consists of a central
subsystem responsible for medium and long term forecasting and control over the whole area concerned.
At this level, the traffic light reference plans and also the criteria needed for the adaptive co-ordination are
calculated dynamically. In addition, a continuous diagnostic activity is carried out for the whole network.
The lower level consists of a network of Multifunctional Out-stations (MFO) with the function of Local
Controllers. These are interconnected, and each is responsible for the management of one intersection.
Local Controllers determine in real time the sequence and optimum length of traffic light phases, using the
co-ordination criteria established by the upper level, traffic measurements detected locally and information
received from the Controllers of adjacent intersections.
Traffic responsive UTC systems require vehicle detectors installed in the road pavement. The most common
are Inductive loops, but microwave detectors and video-processing detection systems can also be used.
Inductive loops are also occasionally used to measure traffic volumes, detector-occupancy and speed.
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Information flows in the SCOOT UTC system
In the central control room, UTC systems generally provide graphic display facilities, which enable the
operator to have a fuller understanding of the current traffic situation in the control area or consult reports
of historical data. These may include diagrams giving information about queue build-up and dispersal,
displays of individual junction operation and time distance diagrams, to assist in analysing traffic flow and
journey times.
Screenshots of the UTOPIA Graphical Interface
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Impacts
The principal impact of UTC systems regard safety and traffic efficiency (the reduction of travel time and
congestion), which has a further indirect impact on the environment. While the co-ordination of traffic
signals improves reduces waiting times at lights and increases the effective capacity of the network, this
increased efficiency may encourage new trips: a phenomenon sometimes referred to the ‘rebound effect’.
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To minimise this effect, it is necessary to combine traffic control systems with demand management
strategies such as road pricing and parking restrictions, or capacity restrictions, e.g. access control and
dedicated bus lanes.
CRITERION
IMPACT
COMMENTS
MEASURED
LEVEL
TRAFFIC
EFFICIENCY
*****
PT EFFICIENCY
***
MODAL SHIFT
AIR
SOLLUTION
IMPACTS*
Well-designed traffic control systems can Sidney
significantly improve traffic efficiency by  up to 24% decrease of traffic
flows during peak hours.
reducing travel times and reducing queues
and congestion.
Quartet Plus (1998)
Impact of distributed traffic
The smoother flows also distribute traffic
adaptive UTC system:
across the network more efficiently
 50% reduction queuing time
 16% average travel time
saving (private traffic)
 Up to 30% travel time
savings during peak hours
Quartet
Plus (1998)
Improved traffic flows also benefit buses.
Impact of distributed traffic
adaptive UTC system:
 20% average speed increase
for public transport
 28% speed increase for PT
during peak hours
Without effective demand management
measures, UTC can lead to greater traffic
volumes as a result to reduced travel times.
***
The reduction of queues and congestion
can reduce pollution, especially CO2, as
this is directly proportional to fuel
consumption.
SAFETY
OF **
VULNERABLE
ROAD USERS
The safety of VRUs is improved when UTC
systems have specific phases for
pedestrians or cyclists.
CONVENIENCE
N/A
Verona
 About 14% less fuel / CO2
(2009)
[*, ** or *** indicate the strength of the impact]
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Integration potential
An Urban Traffic Control system is generally considered to be the basic building block for ITS in an urban
area as it can beneficially be interfaced with many other ITS systems, including:
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Public Transport Management Systems
Incident Management Systems
Supervisory Management for the transport network
Travel Information Services
Emergency Service management Systems
When a UTC system is integrated with a Public Transport or Emergency Vehicle Management system, it is
possible to give priority at intersections to buses, trams or emergency vehicles (e.g. ambulances). The
priority may be absolute (vehicles are always given priority over other traffic) or selective (only in certain
circumstances (e.g. buses/trams that are behind schedule). A further advantage of integration with the
public transport management system is that the availability of traffic information can greatly improve the
accuracy of the information provided to passengers (e.g. arrival time estimates for buses).
When a UTC system is integrated within an extended Transport Management Platform, the traffic data
becomes an integral part of the network management and can be used to calculate the strategy for variable
message signs, real-time driver information systems, route guidance and parking guidance and information
system (see ‘Integrated Platforms’).
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Implementation
Implementation of a UTC system involves the set up communications networks (LAN and WAN) as well as
the installation of the central control equipment and local controllers. After installation of the software,
careful calibration is required to optimize the system. Even when the system is operational, ongoing
maintenance is required, in particular to ensure the good performance of the traffic detectors, which may
be damaged by general wear and road works.
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Examples
a) in previous large events
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Sydney Coordinated Adaptive Traffic Systems(CATS)
The Sydney Coordinated Adaptive Traffic System (SCATS) implemented in the city in 1974 was upgraded by
the Roads and Traffic Authority (RTA) of the Australian State of New Wales to an advanced version (SCATS
6) to manage Olympic Games and normal traffic complementarily and leave long term legacies in terms of
improved transport management. The 2000 Olympic and Paralympics Games in Sydney created the largest
demand for passenger transport ever experienced in Australia: over 6 million spectators in 16 days (over
550,000 on the busiest day). A key decision for the event planning was that spectators should move almost
entirely by public transport trough a new transport management centre (TMC) along with a huge expansion
of public transport supply involving both the City Rail network and the bus fleet serving special spectators
routes.
The new TMC was designed to:

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Control road traffic more effectively
Reduce congestion
Improve bus services
Delivery timely information to road users
Detect incidents and make faster consequential adjustments to traffic flows, using 320 new CCTV
cameras.
The system mostly analyses real-time traffic data from vehicle detectors and produced signal timings
suitable for prevailing traffic conditions. The transport management for the Olympic Games was a success:
no routes experienced increased traffic during the Games and most arterials experienced up to 24%
decreases during peaks. Polls showed “good” or “very good” ratings of 86% for public transport and 76%
for traffic conditions.
Further information at www.rta.nsw.gov.au
b) in more general context
Edinburgh, 'Greenways' (Bus Priority Measures)
As part of a wider package of measures to reduce traffic congestion and improve local bus services,
'Greenways' were introduced on key routes throughout Ediburgh
Background and objectives
The problem of traffic congestion in Edinburgh has been acutely felt in the 1980’s and 1990’s, causing
unacceptably high pedestrian accident rates, unpleasant conditions for pedestrians and cyclists, noise
and pollution, pressure on parking space, higher business costs and a slower journey into work for
many commuters. However, during the period 1986 to 1994 private car ownership in central Edinburgh
soared by 37% against an average rise in the UK of only 19%. Increasing dependence on private cars has
led to more congestion for public transport in a vicious circle which grinds down the public transport
level of service for those without a car.
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The "Greenways" scheme, along with other public transport initiatives, was introduced with the aim of
restoring the balance of car use and public transport. The "Greenways" primary aim is to improve the
reliability and speed of bus services. It aims to cut bus journey times by at least 10% and thus to
encourage more people to abandon the car in favour of the speedier and more reliable bus services. At
the same time, it will be helping to achieve the Council’s objectives of reducing pollution, as buses are
many times ‘cleaner’ per passenger. "Greenways" is an integral part of the Council’s "moving
FORWARD" strategy which aims both to develop an efficient public transport system and also to create
a "Safer, Cleaner and Better" environment in which the city’s inhabitants and businesses can prosper.
Implementation
"Greenways" are controlled under the City of Edinburgh Council Greenways Order 1997. The order was
finally approved by the Scottish Office, with certain modifications, in February 1997. Only then could
the physical implementation work commence. The target date for Phase I (the first two routes) to
become fully operational under the Greenways Order was 04/08/97. For the Greenways scheme to
work, rules regarding access, parking, loading and stopping on the Greenway route have to be enforced
and Lothian and Borders Police have been responsible for this.
Key elements of the scheme, include:
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Greenways bus lanes were painted green and made highly visible
Large explanatory road signs have been placed at the start of the routes; which are marked by
continuous double or single "no stopping" red lines at the edge of the route
New parking and loading bays, with new regulations, have been established
More cycle lanes have been provided; with advanced start positions to give priority for cyclists
at traffic lights
More bus shelters and bus stop information provision is an integral part of the upgrading of
passenger facilities
On the issue of road safety, more pedestrian crossings and raised level crossings have been
installed; together with traffic calming measures in the side streets.
An electronic detection system has been installed in the road surface at 25 traffic signals on the
routes giving buses, fitted with transponders, priority at traffic lights, further improving journey
times
Cameras will also be fitted to buses, to catch offending motorists and assist the manual
enforcement by the police.
Phase I(a) of the scheme (A8/Glasgow Road and Leith Walk) consists of 13 km of Greenways bus lanes
which have been provided at a cost of £4.5m. Completion of Phase I(b) will give an additional 13 km of
bus priority lanes at a further cost of £3m. The whole scheme will give 26 km of Greenways bus lanes at
a total cost of £7.5m. The principal Greenways bus operators, Lothian Region Transport and First Bus,
have invested heavily in the latest, low emission buses (£8m by LRT alone) which are operating on the
Greenways routes. A Quality Partnership agreement has been signed between the main bus operators
and the Council; with both sides pledging assistance in providing the highest standards of public
transport.
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The "Greenways" scheme is one of three major developments now going ahead to improve Edinburgh’s
urban environment and public transport efficiency. It has been effective since 4 August (1997) on two
of Edinburgh’s main routes into the city centre, the A8/Glasgow Road corridor and Leith Walk. This is
Phase I(a) of the project. Three more "Greenways" routes are to follow in the autumn of 1998: the
A70/Slateford Road; A71/Gorgie Road and A702/Lothian Road corridors. This will complete Phase I(b)
of the project. Further schemes covering the remaining radial routes will follow in due course.
Results so far
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Buses are encountering fewer delays whilst using the extensive bus lanes which are no longer
blocked by illegal and dangerous parking
Buses are encountering fewer delays at junctions because of the devices on the buses changing
the traffic lights and the construction of ‘Bus Boarders’ has assisted them in remaining within
the main traffic flow; without the need to pull in and out of bus lay-bys.
The eradication of delays should result in shorter journey times and a more reliable service.
Improved facilities at bus stops, including new shelters and planned passenger information
panels, is assisting both current and potential passengers.
Conclusions and lessons learned
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The chief obstacle in the planning stage of the project was the length of time it took for the
Greenways Order to be approved by the previous Secretary of State for Scotland.
During implementation, there has been some conflict with local residents and businesses; with
regard to the parking and loading restrictions; although designated bays have been provided.
Operational problems have included speeding buses and taxis but these have now been
identified on camera and dealt with by the Police.
There has also been conflict between buses and cyclists in the designated lanes; with some
intimidation of cyclists by bus drivers.
Some bus passengers have been complaining of long stationary periods for buses because the
actual bus journey times have been reduced but the schedules have not been amended. This
indicates an urgent need for re-scheduling and re-timetabling by the bus companies.
Finally, there was a dispute with the traffic wardens over remuneration and the enforcement of
Greenways but this has now been resolved and they are to take over from the Police. However,
continued effective enforcement is still the key to the success of the scheme.
The Greenways scheme would be suitable for any city wishing to upgrade a largely bus-based
public transport system with the aim of encouraging modal shift from car to bus by alleviating
congestion and increasing bus service efficiency
Continued effective enforcement is the key to the success of the scheme.
Greenways is an example of a public transport service improvement; in combination with improved
conditions for pedestrians and cyclists; at a comparatively low cost. The disadvantage is that it only
covers a comparatively small number of routes, although there is scope for expansion and it is flexible,
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and it has to be utilised in conjunction with other public transport schemes such as the planned CERT
Busway and Park and Ride schemes.
Installation of a traffic management solution for Brunswick, Germany
The challenge: The city of Brunswick needed an advanced traffic
management solution enabling it to intelligently manage traffic flow and
provide traffic information to travelers. The system would reduce
congestion and increase safety.
The solution:
•
Installation of loop and infrared detectors for accurate traffic situation recording
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Installation of LED information boards for the display of traffic information
• Installation of a traffic management solution that integrates existing subsystems like parking
guidance systems, traffic computers, public transport control centers, roadwork management systems,
etc.
• Implementation of a TMC/RDS interface for transmitting traffic information from the traffic
management system to the state traffic warning service and thus to all media channels
The implementation : The project was completed in two phases. In phase 1 (August 2000 to July 2002)
the center components with the operating stations were set up and linked up with the traffic
computers and the parking management system. About 100 infrared detectors and 20 induction loops
record the traffic in a section of the city and forward the information to the strategic control system,
STRAMO. The information is then distributed via a variety of channels: two LED boards in the urban
zone, e-mail, fax and the city’s website.
In phase 2 (as of April 2004) the system was expanded. 200 additional detectors ensure that traffic flow
information is available for all vital arterial roads in Brunswick. Six additional LED boards and a userfriendly internet information site (displaying average traffic volumes, car park occupancy, interactive
city map with aerial imagery) were also part of this second phase.
The link-up to the traffic computer is designed as a bidirectional interface so that switching
recommendations can be transmitted to the traffic control computer. Via additional interfaces,
incoming data from the PT control center, the roadwork management system and the pay-and-display
machines control center are made available. This provides information about:
•
Stops and stations (lines, departure times, delays)
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Roadworks (location, duration, description)
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Car park capacity (current occupancy and trends)
Key component: One highlight feature of the Brunswick system is the real-time distribution of traffic
information. This was made possible by the RDS/TMC interface. So-called “location points” were
defined within the relevant city section as a basis for this functionality.
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LOS (level of service) values collected by the measuring stations are analyzed and provide information
on traffic density and flow. During slow-moving traffic or congestion, automatic notifications are
generated in this format and sent to the state traffic warning service. As soon as they arrive there they
are made available to all other state traffic services, radio services, and any car navigation systems with
the required capability.
The result: The congestion warnings on the information boards combined with the incident and action
plan management considerably improve road traffic safety in Brunswick. The information services
provided via internet portal, information boards and navigation systems as well as the active traffic
interventions help reduce congestion or even avoid it altogether.
 UTC in the City of Verona
Verona is a tourist destination in the north of Italy but also an important business centre and major node
on the European transportation network. Increasing mobility demand were leading to growing problems of
congestion especially during commercial exhibitions and when cultural events were held in the Roman
arena.
In order to coordinate traffic more efficiently, a traffic-adaptive UTC was installed in 2009 and a control
centre set up. Information was available to operators not only on traffic flows, but also parking space
availability, VMS panels and city centre access.
Verona: Series of measurements made of trip times UTC impact: 28.9% reduction in average travel time and
estimated 14% reduction in emissions.
along route in the city centre
 UTC in the City of Bucharest
Rapidly growing rates of car ownership in Bucharest
resulted in severe traffic congestion by late 1990s
and also high levels of pollution. As part of a very
large scale traffic management, a traffic responsive
UTC (UTOPIA) was installed at around 100
intersections. It also provided selective, weighted
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and absolute priority to 300 public transport
vehicles and emergency vehicles.
In independent survey in 2010 showed reductions in travel time on the main axes across the city. In some
cases this was particularly marked in the evening rush hour.
In independent survey in 2010 showed reductions in travel time on the main axes across the city. In some
cases this was particularly marked in the evening rush hour.
Bucharest: travel time measurements
UTC impact: trip times reduction on cross axis especially
in evening peak
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