Conventional Traffic Management

This measure was fully updated by THE ASSOCIATION FOR URBAN TRANSITION - ATU in 2014 under the CH4LLENGE project, financed by the European Commission.


Conventional Traffic Management involves measures designed to affect the movement of traffic on a network. Measures include route restrictions and right of way restrictions which serve to alter the direction and movement of traffic as well as parking (and stopping restrictions) which allow for unhindered traffic movement on roads. These are all  implemented with the objective of smoothing traffic flow and increasing safety and do so by making better use of the existing infrastructure.  More specific forms of traffic management designed to improve the environment, enhance safety or reduce travel demand are considered separately.

Conventional traffic management measures can lead to smoother driving conditions, reduced congestion and fewer accidents), and may also achieve environmental improvements, but they may also result in some adverse impacts by reallocating road space or re-routeing traffic. In particular, higher traffic volumes may be introduced to certain streets, and local access may be reduced in order to benefit through movement. Hence the contribution to policy objectives may not always be positive. As a result, in designing a traffic management plan, it is important to understand the conflicting demands between various groups of users who are intending to share the road space.

Because conventional traffic management measures have been in place for some time, there is a lack of recent case study evidence on their performance.

Terminology

“Traffic management includes all physical measures designed to influence the movement of traffic on an existing network” (Thomson, 1968). Traffic management seeks to facilitate efficient and safe traffic flow by modifying the way in which the available road space is used.  In doing so it can place restrictions on traffic movement. The objective therefore is to design a traffic management plan that balances the increased efficiency and safety of some movements with the delay to others arising as a result of the restrictions.

These restrictions fall into the following four categories following the classification of Thomson (1968):

  1. route restrictions; (e.g. one way systems)
  2. right of way restrictions (e.g. priority regulations or signals) including junction redesign
  3. parking restrictions (which may include stopping/waiting restrictions)
  4. speed limits.

The last of these is considered under accident remedial measures. Traffic management can also be applied to achieve other objectives, which are covered elsewhere, including:

Some specialised applications of traffic management are covered elsewhere, but are designed to satisfy the first principles set out below:

For all of these measures, enforcement may be an issue when restrictions are imposed. For example, a ban on a right turn might be easily ignored by drivers and therefore it is also crucial to consider the issue of enforcement in a traffic management plan unless the measures are self enforcing.

This note is concerned with permanent forms of traffic management and does not focus on “temporary traffic management” e.g. measures which may be used when construction or road works are in progress.

Technology

There is an entire spectrum of technology that can be employed for the purposes of traffic management. The most basic form of traffic management technology is signing; regulatory signs are enforced by traffic laws (e.g. one way street signs or signs banning turns). Traffic management can also involve the placing of bollards to prevent vehicular access (in the case of pedestrian zones). These bollards can be raised and lowered to enable certain exempt vehicles to enter the area as appropriate. At the more advanced end, electronic matrix displays may be used to direct traffic e.g. to parking places which allow dynamic display of availability of parking places. Other forms of technology can be used to implement advanced signal control. Enforcement of traffic management measures can rely on labour intensive checking or use technology such as automatic number plate recognition cameras.

Why introduce traffic management?

Conventional Traffic Management schemes include one-way streets, junction redesign, banned turns and controls of on-street parking (Thomson, 1968; May 1997; Fitzpatrick et al 2005). The primary objectives of Traffic Management are to increase traffic capacity and safety. Other potential objectives include environmental protection and reallocation of road space to improve public transport and pedestrian movement.

Route Restrictions

Route Restrictions are measures that change the direction and movement of traffic. The most common example of route restrictions pertaining to general traffic is the conversion of a two way street system into a one way system. Even so, there is an ongoing debate regarding whether one way streets or two way street systems are better.

Supporters of one way systems (e.g. Stemley, 1998; Cunneen and  O’Toole, 2005) point out that one way street systems are safer primarily because the conflict points are reduced in one way systems. In addition they argue that capacity is increased due to one way systems. At the same time, the literature (Walter et al, 2000 ; Lum and Soe, 2004) also points out that one way street systems impose additional turning movements at junctions and increases in vehicle miles travelled, both of which can increase the chance of accidents. In practice, some city centres have taken the initiative to convert one way systems into two way systems (especially in North America e.g. Hart 1998 and examples pointed out in Walker et al, 2000). A comparison of one-way versus two-way street systems for city centres was evaluated and an evaluation methodology for considering two-way street conversion was presented in Walker et al. (2000).

Right of Way Restrictions

These generally prevent or regulate certain movement of traffic in junctions. In this category are measures that range from banning right turns, through priority control and signal control to complete junction re-design.

Junction redesign itself can range from painting simple unmarked junctions with priority markings to conversion of priority (i.e. give way) junctions into signalised roundabouts or gyratory systems. In some cases, junction redesign might arise as part of a new road scheme or new development proposal. This is generally the case when anticipated post-scheme traffic flows might be much higher. For example at high traffic volumes, roundabouts do not operate well (Wright and Ashford, 1998). However, the most often cited reason for junction redesign is safety partly because accidents tend to occur primarily at junctions 1.  

With low volumes, roundabouts might be particularly useful since research has found that conversion of priority junctions to roundabouts can reduce accidents. As the volume of traffic increases, signalised intersections become safer than priority junctions. With priority control, traffic on the minor road needs to “give way” to flows on the major road 2. Drivers on the minor road therefore have to wait for a gap in the traffic and the probability of adopting risky driving behaviour tends to increase with traffic flows. Hence it is usually the case that as traffic flow increases, priority junctions are converted into signalised intersections.  

In summary therefore the objective for junction redesign is generally to support anticipated increases in traffic demand at intersections and to improve the safety record at junctions. Principles and guidance on junction design can be found for example in IHT (1997); Wright and Ashford (1998); Slinn et al (2005).

Parking Restrictions

Parking restrictions (encompassing waiting and stopping restrictions) allow for clear operation of a carriageway. If vehicles are parked on street, the effective throughput or capacity is reduced, particularly where parking occurs close to junctions. In addition, drivers slow down naturally when passing parked vehicles due to the potential of opening doors etc. Parked vehicles can also block sightlines and hence obscure other vehicles or pedestrians, increasing the risk of accidents (Yousif and Purnawan, 2004). The same applies when vehicles are waiting (for any purpose including loading).

In cities, where there is competition for street space, parking on the street is provided at the cost of a general decrease in mobility (Forbes, 1998). Parking leads to congestion as the driver slows down to search for a free space, engages in the act of parking itself, or searches for a gap to move off (Yousif and Purnawan 1999). Hence it has been a policy in many city centres since the 1950s not to allow on-street parking especially during peak hours (Forbes, 1998).

Parking restrictions can also serve to speed up the journey time of buses and enable the travel time by public transport services to be competitive against that of the private car. While bus services may never approach the level of segregation of light rail systems for free running, traffic management measures such as clearways and bus lanes allow a degree of separation for buses and such traffic management concepts are always a feature of current interest in bus rapid transit.

Such clearways occur at bus lanes where stopping/waiting/loading and unloading is prohibited). Enforcement can be by means of bus lane cameras or camera devices fitted on to buses.

The availability of convenient parking is a major factor influencing the decision to drive to that destination (DfT, 1996). Thus restricting parking space can have an impact on modal shift, as discussed under parking controls.

1 Preston and Coakley (2008, p24) state that for example in USA, 50% of all urban crashes occur at intersections.

2 Similarly traffic entering a roundabout generally gives way to traffic circulating on the roundabout.


Demand impacts

Responses and situations
Response Impact on vehicle kilometres by car Expected in situations
Route and right of way restrictions will only affect departure time if they significantly reduce peak congestion levels.  Parking restrictions are likely to encourage a switch to times when restrictions do not apply, or demand is lower.
/ Network restrictions will cause rerouting, and are likely to increase vehicle kilometres.  Right of way restrictions may indirectly have a similar effect.  However, increases in capacity through right of way or parking restrictions can encourage traffic to use shorter, but currently more congested routes.
/ This may occur depending on the nature of the trip. Good traffic management that results in less congestion and easier parking in a particular town relative to another nearby town may act as a trip attractor.  Depending on the relative distances, this could reduce or increase vehicle-kilometres.
Traffic management is unlikely to change the number of trips made.
/ If accessibility of public transport improves, or parking becomes more difficult, travellers could potentially switch mode to public transport. On the other hand, increasing efficiency and making traffic flow smoother might encourage people to switch from public transport to cars and therefore lead to an increase in vehicle kilometres travelled.
This is an unlikely response.
If traffic reroutes on to previously quiet streets, some residents might decide to move home.
= Weakest possible response = Strongest possible positive response
= Weakest possible negative response = Strongest possible negative response
= No response

Short and long run demand responses

If service levels are reduced then responses can be assumed to be diametrically opposite to those presented here.

Demand responses
Response - 1st year 2-4 years 5 years 10+ years
-
  - / / / /
  Change job location
- Shop elsewhere / / / /
  Compress working week
- Trip chain
- Work from home
- Shop from home
  Ride share
- Public transport / / / /
- Walk/cycle / / / /
  -
  -
= Weakest possible response = Strongest possible positive response
= Weakest possible negative response = Strongest possible negative response
= No response

Supply impacts

The change in the amount of supply (effective capacity of the road network) depends on the measure applied.

Route Restrictions: One way streets increase network capacity, provided that traffic is not diverted onto excessively long routes, by simplifying junction movements, making more effective use of available road width, and removing friction with opposing traffic.  Typical schemes may increase capacity, in vehicle-km/h, by 10% to 15%.

Right of Way Restrictions: Conversion of priority junctions into roundabouts or signalised junctions can increase capacity and reduce delay for minor movements.  However, the increase in capacity is critically dependent on the design of the modified junction.  Increases in junction capacity, in vehicles per hour, of 10% to 20% are possible.

Parking Restrictions: Implementing (and enforcing) parking restrictions will increase capacity for moving traffic, particularly where parking is removed on the approaches to junctions.  In such cases, increases in capacity, in vehicles per hour, of up to 40% are possible.

Financing requirements

The financing requirements depend on the particular measure applied as well as the coverage of the scheme (effective route length or number of junctions).  Costs will be much higher if additional land is needed, but this would make it no longer strictly a traffic management scheme.  Route restrictions typically require only moderate costs for implementation, largely involving signs and markings, and enforcement costs are typically low.  Right of way restrictions are typically more expensive to implement since they will require some carriageway reconstruction (for roundabouts) or equipment (for signals); again, they are inexpensive to operate.  Parking restrictions cost little to implement, but have a continuing enforcement cost if they are to be effective. 

Expected impact on key policy objectives

It is clear that the actual impact of conventional traffic management depends on the measure used. Equally, it is crucial to emphasise that whilst a measure may solve a problem in a local area, it may lead to the emergence of problems elsewhere.

This is the same view articulated in DfT (1996) where it is stated that “Traffic management schemes can affect vehicle emissions by altering the volume, speed and composition of the traffic stream and the driving pattern (steady speed, stop/start, acceleration and deceleration).  There is also the need to recognise that, whilst traffic management schemes may be able to reduce the impact of traffic on air quality in the immediate locality, they may have a relatively small city wide effect.”

Contribution to objectives

Objective

Scale of contribution

Comment

  / Increase in public transport service levels – reduction in the waiting times & overcrowding experienced by existing passengers and so a reduction in the generalised costs of travel. Public transport becomes a more attractive mode of transport and will encourage car users to switch, helping reduce traffic congestion. Note the degree of mode switch depends upon the service level cross elasticity between car and bus.
  / If the increase in service level does indeed achieve significant mode switch from car this is likely to reduce local air and noise pollution and perceptions of danger.
  / Increase in service levels - will lead to some mode switching from car and so help reduce air and noise pollution. Note the amount of switching depends upon the service cross elasticity between car and bus.
  / Extension of service – allows a wider range of services, goods & opportunities to be accessed. Additional new services may be focused in particular areas currently not served by bus or to new destinations that better meet user’s needs.
  Will lead to some mode switching from car and so help reduce accidents. Note the amount of switching depends upon the service cross elasticity between car and bus.
  / The generalised cost of travel by public transport will be reduced directly by the improved service level. Furthermore, mode switch from car may reduce congestion levels so leading to further reductions in travel time. These two impacts may increase productivity. On the other hand if the improvements require increased subsidy then the necessary increase in local taxes may stifle economic growth.
  Financial impact on the operator will depend upon the service level elasticity. A service level elasticity greater than one will lead to a net increase in revenue, if it is less than one there will be a net decrease.
= Weakest possible positive contribution = Strongest possible positive contribution
= Weakest possible negative contribution = Strongest possible negative contribution
= No contribution

Expected impact on problems

Contribution to alleviation of key problems

Problem

Scale of contribution

Comment

Congestion-related delay

/ Low cross elasticities between changes to service levels and modal switch may limit the impact on congestion from an increase in service levels.

Congestion-related unreliability

/ An increase in service frequency will help combat unreliability amongst public transport users. Mode switching may also reduce road traffic related unreliability.

Community severence

/ Due to possible reduction in traffic levels.

Visual intrusion

/ Due to possible reduction in traffic levels.

Lack of amenity

Due to possible reduction in traffic levels.

Global warming

/ By reducing/increasing car traffic-related CO2emissions. This is likely to outweigh any increase in public transport emissions.

Local air pollution

/ By reducing car traffic emissions of NOx, particulates and other local pollutants. This will outweigh any change in public transport emissions.

Noise

/ By reducing traffic volumes.

Reduction of green space

Reduction in congestion may reduce pressure for roadbuilding.

Damage to environmentally sensitive sites

Due to reduced traffic and possibly reduced pressure for roadbuilding.

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

/ An increase in the service levels will improve accessibility to goods, services, education and employment for people without a car and some with mobility impairments.

Disproportionate disadvantaging of particular social or geographic groups

/ An increase in the service levels will improve accessibility to goods, services and employment for the socially excluded with no car available and those that live in the areas served. The effect will be especially important if network coverage is increased for those in areas that had no service previously.

Number, severity and risk of accidents

By reducing traffic volumes.

Suppression of the potential for economic activity in the area

/ The generalised cost of travel by public transport will be reduced directly by the improved service level. Furthermore, mode switch from car may reduce congestion levels so leading to further reductions in travel time. These two impacts may increase productivity. On the other hand if the improvements require increased subsidy then the necessary increase in local taxes may stifle economic growth.
= Weakest possible positive contribution = Strongest possible positive contribution
= Weakest possible negative contribution = Strongest possible negative contribution
= No contribution

Expected winners and losers

Winners and losers

Group

Winners/Losers

Comment

Large scale freight and commercial traffic

/ High value freight journeys – less time spent in congestion the greater the vehicle utilization, however a relatively small proportion of the journey distance is in urban conditions. Service increase reduces traffic congestion so is beneficial. This depends upon the size of the service cross elasticities between car and bus.

Small businesses

/ Service increase – encourages trips to non local areas.

High income car-users

High incomes associated with high value of time and thus continued car use for high value journeys. These journeys will benefit from reduced congestion. A service increase reduces traffic congestion so is beneficial. This depends upon the size of the service cross elasticities between car and bus.
People with a low income / Unlikely to have car access. An extension of the service will increase the range of services, goods and opportunities open to them whilst an increase in frequency will reduce the generalised cost of travel by public transport.
People with poor access to public transport If changes in service levels are restricted to existing services then no impact. However, if new services are implemented serving different areas then a very positive impact.
All existing public transport users / Service increase – will lead to reduced generalised costs of travel (e.g. reduced waiting and overcrowding) & more opportunities to travel if the service is extended.
People living adjacent to the area targeted / Service increase - they may benefit from reduced congestion and improved or increased public transport supply.
People making high value, important journeys / Reduced generalised costs of public transport and reduced congestion will result in valuable time savings. A service increase reduces both so is beneficial.
The average car user / Reduced congestion will result in valuable time savings. A service increase reduces both so is beneficial. This depends upon the size of the cross elasticities between car and bus.
= Weakest possible benefit = Strongest possible positive benefit
= Weakest possible negative benefit = Strongest possible negative benefit
= Neither wins nor loses

Barriers to implementation

One of the primary difficulties with traffic management implemented on its own rather than in a package of measures is that traffic management might introduce some adverse impacts such as traffic rerouting and environmental intrusion onto quiet streets. Even if journey speeds are increased by traffic management measures, the journey length may have increased and this could result in no change in travel times 3. In addition, there could be reduction in accessibility for certain users e.g. when one way streets are introduced, buses might have to be rerouted. Emergency services might also adversely affected (Stemley, 1998).

It must be borne in mind that while the local (i.e. treated) area generally improves, there are often adverse impacts of these measures on other areas (e.g. parallel routes). 
While the intention is the restriction of movement for treatment in the local area, there will naturally be a rerouting onto other parts of the highway network. Hence procedures for handling this must be handled carefully at the design stage (May, 1997). For example, introducing one way street systems could lead to a more complex and circuitous route for through traffic.  Drivers might also be tempted to seek out “rat runs”. In general increased journey lengths would increase fuel consumption as well.

Similarly whilst vehicles are not generally obliged to stop at “priority junctions” when conflicting traffic is clear or they have priority (and hence avoid idle queuing), vehicles have to stop at the red light and subsequently accelerate, resulting in excess fuel consumption that produces additional carbon emissions (Peters et al, 2009).

Parking restrictions could potentially increase the search costs for parking as spaces (which could be in front of shops etc) may be removed. Vehicles may then have to intrude on neighbouring streets (if the ban is not applied there).

It must also be recognised that traffic management effectively increases the supply of road space to some road users (although it might reduce it for others). To the extent that the supply of capacity for private car users is increased then this implies that the cost of driving is actually reduced. By encouraging a smoother flow of traffic, there is potential to therefore increase the total number of trips made by private car. Obviously this will depend on the exact elements of the package implemented.

3 This is one of the arguments for the constant travel-time budget literature (Zahavi, 1974).

Scale of barriers
Barrier Scale Comment
Legal The only requirements are for regulations permitting the traffic management scheme. 
Finance Some traffic management measures require comprehensive redesign of street layout.
Governance Traffic management responsibilities usually rest with a single body.
Political acceptability Politicians may react to objections from those whose movements are restricted.
Public and stakeholder acceptability Those whose movements are restricted may object.
Technical feasibility Most traffic management measures are simple to design and operate.
= Minimal barrier = Most significant barrier

Catford Traffic Management Study

The source of this case study is Pearce and Stannard (1973) and Catford Town Centre Local Plan (Proposed Submission 2013).

Context

Catford is a district of London, the town centre of the borough of Lewisham. The layout of Present Day Catford is shown in Figure 1. The roads that are labelled on Figure 1 were previously two way streets up to 1970 when they were converted into a one way system. The case study analyses the impact of that conversion. The following were also implemented alongside the one way system.

  1. a large number of parking spaces along Plassy Road were removed
  2. parking restrictions were introduced on Sangley Road and Brownhill Road
  3. bus stops had to be relocated.

Fig1
Figure 1: Present Day Catford (Greater London United Kingdom)
Source: Google Maps

In 2013, the Council proposed a “Submission Version” of the Catford Town Centre Local Plan; it is the version the Council has prepared following public consultation earlier in 2013 on a ‘further options report’ and responds to the comments and suggestions that were made. It is this version of the Catford Plan that the Council intends to submit to the Secretary of State who will then appoint an independent Planning Inspector to determine whether the plan is ‘sound’ and can be adopted by the Council.

 

The aim of this Plan is to secure improvements in movement to, through and around Catford by taming the South Circular in ways that better manage traffic and benefit pedestrians, cyclists and bus and rail users.
It also gives qualified support for extensions to the London Underground Bakerloo Line and Docklands Light Rail and sets out a town centre car parking strategy. The range of transport improvements need to be coordinated as the proposals outlined for the town centre are expected to result in an increase in the numbers of people who shop and visit Catford as well as those who live here.
The Council, in conjunction with Transport for London, will progress the following proposals:

  1. widening Sangley Road (making use of part of the existing highway reserve) to provide an eastbound contra-flow bus lane to significantly reduce the journey time for these routes and to reduce the volume of buses on Rushey Green northbound. This would be facilitated by introducing an eastbound bus only right turn at the junction of Catford Road and Rushey Green;

altering the junction between Catford Road and Rushey Green to simplify pedestrian crossings, improve traffic flows and improve public space outside the Broadway Theatre;

  1. The one-way southbound operation on Plassy Road would be maintained, with a revised junction at the southern end, to facilitate the contra-flow bus lane on Sangley Road and maintain the one-way eastbound operation on Brownhill Road;
  2. To improve traffic and servicing access to a new shopping centre located on the Catford Centre site, improvements are required to be made to the junction of Thomas Lane and the A205 Catford Road;
  3. The Council will secure the overall amount of public car parking spaces that reflects both Catford’s excellent public transport accessibility and the need to support a vibrant town centre economy and manage spaces in ways that gives priority to those that need them most, by requiring Car Park Management Plans for all proposed public car parks to demonstrate how the design and management of spaces would prioritise disabled people and those with children.

Figure 2: Key buildings and streets in Catford. Source: Catford Local Plan

Impact on demand

Table 1 shows the vehicle flows over an typical day before and after the introduction of the original scheme.

Table 1: Vehicle Flows) on a typical day (between 0700-1900) before and after scheme implementation

Road

Before

After

Change

Percentage Change

Rushey Green (North of Catford Road)

30,140

18,516

-11,624

-39%

Rushey Green (South of Catford Road)

18,235

18,318

83

0

Brownhill Road

13,742

18,240

4,498

33

Plassy Road

834

17,147

16,313

1,956

Sangley Road

5,400

17,996

12,596

233

The alignment of the A205, which forms the South Circular, runs through Catford in a one-way gyratory system with traffic using Rushey Green northbound, Brownhill Road eastbound, Plassy Road southbound and Sangley Road westbound. This results in the Plassy Road Island site suffering severance and a highway-dominated environment with fast flowing one way traffic. Similarly, the pavement areas next to Catford Road and Rushey Green are dominated by the highway requirements to facilitate traffic flows through Catford, rather than servicing the town centre itself.
Following the introduction of the one way street system, total vehicle volumes rose by around 16000 per day of which approximately 3300 were heavy goods vehicles.

Today, the town centre has excellent public transport provision by train and comprehensive bus network. The enhancement of public transport infrastructure and services will improve Catford’s accessibility and encourage an increase in its use. Reducing reliance on car use and relieving pressure on roads and car parking has the potential to reduce air pollution levels and generally contribute to the environmental sustainability objectives of the Catford Plan.

Impacts on supply

No carriageway widening took place except for provision of additional crossing facilities. In essence therefore the system converted a series of two way roads into one way streets. As a result the capacity of the network was increased, though the scale of increase was not measured.

Contribution to objectives

Contribution to objectives
Objective Scale of contribution Comment
  Vehicle Hours were reduced by 34% due to the one way system. However the one way system also increased vehicle miles travelled by about the same percentage (35%). While there must have been time savings, these would have accrued to private cars. On the other hand, 55% of pedestrians, car and bus users felt that their access was worse if attempting to access “the island” created by the one way system.
 

Increased traffic noise was the main concern of residents in the survey area. Kerbside noise levels more than doubled during the weekday.80% reported that they heard more noise than they previously did and almost half were disturbed by the noise in the sleep.

However on Brownhill Road and Rushey Green there were some perceptible reductions in noise level as well.

  Increased pollution was also thought to be an effect of the scheme, though no measurements were taken.
  For mothers with children who had to cross Plassey Road to get to the Rushey Green primary school on foot, there was an increased perception of danger due to the volume of traffic.
 

There was a 40% decrease in accidents from 117 to 70 (comparing 2 years before against two years after implementation) and a 42% reduction in casualties (using the same basis of comparison 132 to 77).

There was a 50% reduction in accidents involving pedestrians.
  Some businesses felt that being located on the island had led to the loss of business and in general 40% thought that the number of customers had decreased.
  The scheme cost around £63,000 in 1970 prices. Catford Local Plan doesn’t provide any financial parameters.
= Weakest possible positive contribution = Strongest possible positive contribution
= Weakest possible negative contribution = Strongest possible negative contribution
= No contribution

Turning on Red (LTOR), Singapore

Context

In Singapore, traffic signals are the dominant type of traffic control with more than 1100 traffic installations. Singapore follows the British practice of driving on the left hand side of the road (unlike much of Europe or US). The policy of the Land Transport Authority (LTA) is that where possible and land space permits, dedicated channels of left turn slip roads are constructed so that vehicles intending to turn left can do so and merge with the cross flow under priority conditions. 

This case study examines the impact of a traffic management measure that allows for vehicles to turn left, after giving way to pedestrians and conflicting traffic even though the red indication is on.  This Turn on Red measure originated in the USA (and in that context, it is known as right turn on red since driving is on the right hand side of the road). In fact by 1947, California had allowed right turn on red unless expressly prohibited by traffic signs.  In 1997, the LTA implemented a traffic management measure known as Left Turn on Red (LTOR) at 50 intersections.

The anticipated benefits of turning on red, in common with other conventional traffic management measures, are primarily to reduce vehicle delays at intersections, reduce pollution and reduce energy consumption. It was also hoped that there would be a small increase in intersection capacity. At the same time, there was the fear that Turning on Red might lead to an increase in accidents and their severity. Hence several criteria were used to select junctions where this scheme was to be implemented as follows:

  • Adequate sight distances particularly on approach to the intersection to allow road users to have a good, clear view of the surrounding traffic situation;
  • Not obstructed by on street parking
  • High volumes of traffic using the LTOR lane
  • Only junctions with low accident history were eligible for the implementation;
  • Geometrics/lane arrangement: LTOR movements from a single lane with adequate (non-acute) turning radius and wide receiving (entry) lanes;
  • Pedestrian/vehicular activities: A generally low number of crossing pedestrians and away from routes often used by young, infirm and disabled persons such as in the vicinity of primary schools, retirement homes, hospitals, etc.

Its intended operation was such that vehicles cannot turn left on red unless expressly allowed by the traffic signs. The signage and general operation of the scheme in Singapore is shown in Figure 2.

Fig 02

Figure 2: Junction Layout and Signs for LTOR (Source: Wong et al 2004).
In February 1999, the LTOR signage was enhanced by replacing the previous “GIVE WAY—Left Turn On Red” with “Left Turn On Red—STOP Before Turning.”

Impacts on demand

Wong et al (2004) suggest that traffic volume increased on the approach roads where LTOR was implemented. The reason for this is unclear and could be due either to traffic rerouting to take advantage of this measure or it could have been due to generated traffic. 

Impacts on Supply

The main impact in effect was to reduce the vehicular delays on the approach road. Wong et al (2004) reported reductions in delay (measured in seconds per vehicle) on the approach road of between 73 to 86% for 3 typical junctions where LTOR was implemented.

Impacts on safety

The evidence on increased accidents is mixed. On the one hand, accidents increased by 17% after LTOR adoption (for a sample of 36 sites surveyed) yet serious injury accidents fell by 62%. However addition, moving vehicle collisions increased by 38% but there was a large reduction in the number of vehicle-pedestrian accidents.

Contribution to Objectives

Contribution to objectives
Objective Scale of contribution Comment
  Reductions in delay will have contributed to an improvement in efficiency.
  There will have been little change in liveability, except where pedestrian movement has been restricted by the scheme.
  No direct evidence was provided, however it is likely that there will have been little change in mode choice.  The slight increase in flows may have caused minor increases in pollution.
  There will have been some adverse impacts on pedestrians.
  The results indicate an increase in all accidents but a reduction in serious injuries.
  No direct evidence was provided.
  These schemes are inexpensive to implement.
= Weakest possible positive contribution = Strongest possible positive contribution
= Weakest possible negative contribution = Strongest possible negative contribution
= No contribution

Gaps and Weaknesses

All of these traffic management measures have been in place for some considerable time, and there is a lack of recent documented case studies.

Expected contribution to objectives

Contribution to objectives
Objective Catford Traffic Management Study Left Turn on Red
 
 
 
 
 
  /
 
= Weakest possible positive contribution = Strongest possible positive contribution
= Weakest possible negative contribution = Strongest possible negative contribution
= No contribution

Contribution to problems

Contribution to alleviation of key problems
Problem Catford Traffic Management Study Left Turn on Red
Congestion
Community impacts
Environmental damage
Poor accessibility
Social and geographical disadvantage
Accidents
Economic growth
= Weakest possible positive contribution = Strongest possible positive contribution
= Weakest possible negative contribution = Strongest possible negative contribution
= No contribution

Appropriate contexts

Appropriate area-types
Area type Suitability
City centre
Dense inner suburb
Medium density outer suburb
Less dense outer suburb
District centre
Corridor
Small town
Tourist town
= Least suitable area type = Most suitable area type

Cunneen M., O’Toole R (2005)  “ No Two Ways About It: One-Way Streets Are Better Than Two-Way” Independence Institute Issue Paper 2-2005
http://www.i2i.org/articles/2-2005.pdf

DfT (1996) “Traffic Management and Emissions” Traffic Advisory Leaflet 4/96 April

Fitzpatrick K, Wooldridge M, Blaschke J (2005) “Urban Intersection Design Guide: Volume 1 - Guidelines", Report No: FHWA/TX-05/0-4365-P2 Vol. 1 http://tti.tamu.edu/documents/0-4365-P2.pdf

Forbes G (1998) “Vital signs: Circulation in the heart of the city--an overview of downtown traffic” ITE Journal 68(8), 26-29

Hart J (1998)  “Converting back to two-way streets in downtown Lubbock.” ITE Journal68( 8), 38-46.

Institution of Highways and Transportation (1997) Transport in the Urban Environment IHT: London

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