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Urban traffic control systems
SummaryFirst principles assesmentEvidence on performancePolicy contributionComplementary instrumentsReferences

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

Change departure time

-1

Increase in peak where reducing travel times and increasing capacity may reduce congestion

Change route

2

Reduce overall where reliability of selected roads improves by minimising total vehicle delays of whole network

Change destination

0

N/A

Reduce number of trips

-1

Where reducing travel times and increasing capacity may attract car users, and may induce re-routing within the network

Change mode

0

Some increase where reducing travel times and increasing capacity may attract car users, but some decrease where priority for public transport improves reliability

Sell the car

-1

Some increase where reducing travel times and increasing capacity may attract car users

Move house

0

N/A

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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

Change departure time

-

0

-1

-1

0

Change route

-

0

2

2

1

Change destination

Change job location

0

0

0

0

 

Shop elsewhere

0

0

0

0

Reduce number of trips

Compress working week

0

0

0

0

 

Trip chain

0

0

0

0

 

Work from home

0

-1

-1

-2

 

Shop from home

0

-1

-1

-2

Change mode

Ride share

0

0

0

-

 

Public transport

0

1

1

2*

 

Walk/cycle

0

0

0

0

Sell the car

-

0

0

-1

-1

Move house

-

0

0

0

0

* 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

Efficiency

3

By reducing delays, improving reliability and prioritising selected vehicles

Liveable streets

-1

By increasing community severance

Protection of the environment

1

By reducing air pollution

Equity and social inclusion

1

By improving public transport conditions

Safety

-1

If congestion is reduced sufficiently to allow increased speed, but reduced stop/start usually reduces accidents.

Economic growth

1

By freeing up potentially productive time currently involved in delays

Finance

-3

By installing and maintaining technological equipment

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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

4

By reducing delays to vehicles and the number of times they have to stop

Congestion-related unreliability

4

By reducing delays to vehicles and the number of times they have to stop

Community severance

-1

If congestion is reduced sufficiently to allow increased speed, severance may increase if there are no mitigating measures.

Visual intrusion

0

-

Lack of amenity

0

-

Global warming

2

By reducing stop/start conditions

Local air pollution

2

By reducing stop/start conditions

Noise

0

-

Reduction of green space

0

-

Damage to environmentally sensitive sites

0

-

Poor accessibility for those without a car and those with mobility impairments

1

By enhancing the reliability of public transport

Disproportionate disadvantaging of particular social or geographic groups

1

By enhancing the reliability of public transport

Number, severity and risk of accidents

-1

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

1

By improving the efficiency of the local road network

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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

1

Where reduced congestion is achieved on routes or areas used by freight vehicles in UTC-based traffic systems.

Small businesses

2

Where reduced congestion and improvement of pedestrian facilities encourages use of local amenities.

High income car-users

1

May benefit from reduced congestion

People with a low income

1

May benefit from reduced congestion

People with poor access to public transport

0

Reduced congestion will improve public transport reliability, but not solve problems associated with poor access for public transport users.

All existing public transport users

2

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

1

May benefit from reduced congestion and pollution

People making high value, important journeys

3

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

1

May benefit from reduced congestion

Barriers to implementation

Scale of barriers

Barrier

Scale

Comment

Legal

0

There are no obvious legal barriers to the introduction of UTC systems.

Finance

-3

Inductive loop detectors are usually used in traffic responsive systems, but installing and maintaining them subsequently are significant in the cost.

Political

0

There are no obvious political barriers to the introduction of UTC systems.

Feasibility

0

Feasibility studies such as cost benefit analysis and financial analysis are required to introduce UTC systems.

 

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Text edited at the Institute for Transport Studies, University of Leeds, Leeds LS2 9JT