Urban areas require the development of integrated transport planning and the categorisation of roads depending on the relative importance of their functions pertaining to traffic and local life.

Two categories of road form the trunk network of the urban area. They are:

• Urban expressways:  motorways, or roads comparable to motorways because they are perceived as such by users owing to their characteristics and conditions of use (separate -of-way, divided carriageways, grade-separated junctions, no entry for some user categories). Urban expressways ensure continuity of major national and regional routes in urban areas
• Other main roads linked to or complementing these urban expressways where the traffic function is dominant and is awarded priority, whilst retaining functional relationships with the urban environment

Characteristics: Trunk networks in urban areas are subject to commuter movements relating to trips between home and work, which give rise to traffic levels causing the road networks to operate at saturation. The slightest incident can result in road congestion, which may rapidly degenerate into gridlock of the route and even of a major part of the urban area. But this network is often interlinked and there may be capacity reserves on some other road sections at all times.

Another feature of these networks is the complexity of responsibilities: there are many participating route owners and operators. Continuous consultation is necessary between authorities in order to:

• adopt a general traffic management strategy for expressways and the associated network (for example, priority to through traffic, or particular classes of traffic, like high occupancy vehicles or buses)
• co-ordinate this strategy with strategies for urban network management (signalised junctions) and public transport
• define possible rules to divert traffic from expressways onto an associated network in the event of excessive congestion due to exceptional events
• provide users with high-quality, reliable, relevant road information enabling optimum use of a network while offering the possibility of an inter-modal choice
• improve safety through enhanced supervision of the main roads and, in the event of disturbances, restore normal traffic conditions quickly
• limit inconvenience to traffic through planning improvements

Operational objective: The aim is to constantly optimise network use and balance competing demands between different classes of road user. The functions to be implemented are the permanent activation of traffic management plans drawn up by all the partners concerned. The network supervision system and information processing must be permanent and automated. This is the network on which the density of equipment for collecting and disseminating information will be the greatest. (See  Urban Traffic Management, Urban Traffic Control and Urban Operations)

These networks include the motorways and associated main road network (parallel roads and alternative routes) that provide high capacity inter-urban motorway corridors and regional networks.

Characteristics: Over these heavily-trafficked corridors, designed for national and international through traffic, flow breakdown is frequent especially at beginning and end of the working week and with the onset of busy holiday periods. Their impacts are great as they concern a large number of users and can have upstream repercussions over long distances. In addition, disturbances on the main arterial roads can quickly extend to the parallel roads.

Operational objective: During incidents, the aim is to maintain the best possible flow conditions through optimum use of the network. It is essential to coordinate action between the management services. The resulting traffic management plans must be studied and implemented jointly, with preventive measures that may be required far upstream of the disturbance. They will be activated during the disturbance.

The functions to be implemented are the same as those of level 1. However, the density of equipment will be lower and it will be positioned according to the operational objectives: automatic incident detection in hazardous areas or detection limited to the most sensitive days; user information by variable message signs upstream of points where an alternative route can be chosen. (See Highway Traffic Management  and Highway Operations)

Characteristics: These networks consist of roads with moderate traffic levels. These roads are characterised by the fact that major disturbances are rare and their impacts are localised. The number of users involved is also limited.

Operational objective: The main aim is to ensure good road serviceability as well as safe driving conditions over the entire network. For the management of random disturbances, it will generally be unnecessary to organise traffic management plans in advance, or to immediately restore normal traffic capacity on the road, but it is advisable to disseminate the best possible information on the level of inconvenience and its foreseeable onset. (See  Travel Information Systems)

The functions to be implemented consist of organising foreseeable road serviceability operations such as winter maintenance, roadwork planning, and the organisation of convoys, events to limit inconvenience to users and information to users before they set out or during their trip. (See  Regional Networks)

In order to make integration of systems work, there must be significant amount of common components among various systems. One way to ensure this is to standardise the interfaces, or rely heavily on existing standards so that there are fewer problems concerning interoperability. For example some ITS systems use the TCP/IP  communication protocol. This would allow for the potential of various other TCP/IP applications to interact with the ITS system in the long run.

Communication standards are the most obvious area of standardisation. Other areas might include the standardisation of digital map formats, data formats of traffic information, and so on.

Obviously, there are various levels of standardisation. What you want to standardise will depend largely on what kind of services you would like to integrate, now and in the future. (See ITS Standards)

Existing Standards versus New Standards:  Sometimes it may prove that the existing data formats or communication protocols are not sufficient. Creating a generic and standard protocol or data exchange format, however, is not a trivial task, especially for network operation applications that are often mission critical. By integrating various services into a single communication protocol, for example, the system would have a single point of failure. The protocol needs to be extremely robust, and the testing that is required ensuring robustness can become difficult as the complexity and the importance of that module increases. In some cases, it makes sense to sacrifice the level of the service in order to achieve integration using an existing and proven standard, rather than trying to create an optimal one.

Obviously, many of the issues concerning integration are not purely technical, but rather institutional. The negotiation between players, the division of labour between the private and the public sectors, the issue of acceptance, all become extremely important in an operator’s decision process.

Standardisation is a considerable step in order to achieve integration of various systems. However, as the complexity of the entire spectrum of services offered increases it becomes considerably more difficult to determine just where to standardise and to what level. In order to make this transparent throughout the system and to aid the network operator in figuring out what components are vital, a system architecture approach is important. This clarifies the relation between various actors and how they interact through whatever channels in order to provide the required services. This helps the road network operator to see the relation between various services, giving them a better approach to their integration efforts. (See ITS Architecture)

Integrating various systems is an effective approach to network operations. There are, however, issues that need to be addressed.

Plan Ahead: Achieving integration as a second thought may prove to be extremely difficult. Once a system is in place replacing it may involve enormous financial and political resistance. If there is any possibility of integrating various services in the future, if at all possible it should be included within various considerations from the beginning. (See Strategic Planning)

In addition, various efforts to bring the players together and reach an agreement require a significant amount of time. Road network operators need to allow time for that negotiation process. (See Inter-Agency Working)

Short Term and Long Term Benefits: An integrated system means that it may be difficult to optimise for a single application or service in the short run. Common and standardised protocols may not be the optimal solution for that particular service. For example, if you only want an ETC system for a single stretch of toll road it may not make sense to consider a common national system, may require a more complex system. It should prove beneficial in the long run, but just how far into the future may differ from place to place, and in the short run it would be easier and cheaper to introduce an off-the-shelf ETC system.

The planning horizon for each road operator will differ. It should, however, be noted that the decision to integrate your system (or not to) would also be affected by that horizon.

The purpose of this measure is to adapt the operation of traffic signals to match traffic flows or to impose a specific regulating policy such as bus priority. This may be used at an intersection located:

• on an arterial road which is subject to traffic variations (peaks linked to seasonal or especially weekend travel)
• on a road temporarily used as an alternate route
• in an area where the traffic management strategy changes over time

The procedure consists of:

• analysing traffic flow dysfunctions to be addressed
• gathering specific traffic data (directional counts, in particular)
• drawing up plans for required signals
• implementing them in the controller, which may require the addition of remote detection or control equipment

Signal plans can be activated in various ways:

• manually
• on a programmed schedule
• by an automated device that may detect local traffic conditions
• by a central system which takes into account not only the local conditions but also the traffic conditions on a zone or even on the whole network

Traffic signal control should also take into consideration all types of users and in particular pedestrians, two-wheeled vehicles and public transport.

This action requires:

• monitoring and correctly maintaining equipment, especially traffic sensors
• periodically adjusting controls to traffic and/or to the traffic management policy
• occasionally reconciling purely local issues and those related to through traffic
• The use of microscopic simulation tools allows quick testing for various strategies together with the visualisation of their impact while verifying quantitatively that various criteria are satisfied: time spent on the network, waiting time for different categories of users

(See Urban traffic Control)

Most large cities in the world are now equipped with traffic signal control systems. ITS is concerned with systems which adapt themselves to actual traffic measurements and situations, either through on-line choice of predetermined control plans or through on-line calculation of tailor-made control plans (and combinations in-between these two).

• Developments in recent years include accounting for saturation through use of expert systems (CLAIRE system in Paris, London) or “gating” approaches (SCOOT) and the accounting of new traffic parameters such as queue lengths at junctions or travel times/delays, measured thanks to ITS-based techniques such as automatic video queue length measurements, automatic video license plate readings and probe vehicles data
• These systems generally also include priority management of public transport and emergency vehicles, and more and more often, driver and user information (park-and-ride, parking occupancy, arrival time of the next bus)

(See Urban Traffic Management)

The purpose here is to adapt the use of available lanes to circumstances. This most often involves handling recurring gridlock on a section of road linked to insufficient capacity of the section, or gridlock when one or more lanes are unavailable. This measure therefore covers the following areas of use:

• sections with a restricted cross-section that is difficult to widen (for example overpasses, underpasses, tunnels)
• convergent or divergent sections that are usually adequate but are poorly adapted to some traffic configurations
• high-risk areas (tunnels, sections subject to rock-slides or high winds)
• construction sites

Some examples of specific uses include:

• reverse direction assignment of a median lane of a two-way road
• use of an emergency stopping strip (hard shoulder) as an additional lane in rush hours
• contra-assignment of a lane on a divided highway (lane used in rush hour or reserved for public transport)
• fast and intermediate lanes banned to heavy goods vehicles (HGV)
• reserved lanes for slow vehicles and/or public transport
• high Occupancy Vehicle (HOV) lanes

The introduction of such a measure requires resources such as automated controls to verify the consistency of instructions provided by various lane assignment signals, a modular barrier, or temporary marking (cones or beacons).

Regardless of the method used, the operation may be cumbersome and complex. Any control systems must be maintained in fail-safe condition. For example:

• the various operating configurations must be compatible with existing mandatory signs and regulations – this often requires replacement of some static signs (especially instructions) with variable signs
• in a reversible lane on a two-way road or in a contraflow lane on a divided highway the risk of head-on collision between opposing flows leads to the installation of a vertical separation devices (beacons or other separators)
• in addition, automatic incident detection methods are very often needed in order to rapidly react to any abnormal situation
• automatic enforcement systems can also be introduced in order to reinforce efficiency and safety for lane control systems

Dynamic lane management (DLM) enables the allocation of lanes to be modified on a temporary basis by means of traffic guidance panels, permanent light signals, multiple-faced signs (DMS), LED road markers, and overhead installation of VMS for signalising lane closures and lane directions.

Fundamental applications of this service are: for tidal flow systems, lane allocation at intersections, lane allocation in road tunnels, hard shoulder running. (See  Highway Traffic Management)

These systems are put into operation on a daily basis during peak periods where there is recurrent congested with available capacity in the opposite direction (1 lane minimum) .This sometimes means in practice the use of special equipment to move the central concrete safety barrier, although some tidal flow schemes simply use signing systems such as variable lane assignment signs placed on gantries. For practical reasons, the lane direction changing is generally made on a fixed-time basis (each day at predetermined hours), although several cities in the United States have implemented a concept known as “managed lanes”, that allows more dynamic reversal of lane directions.

As far as ITS is concerned, dynamic reversal of lane direction can be made with systems using gantries. Lane reversal should always be subject to operator’s validation. The implementation of the tidal flow remotely by the operator, can be eased by the use of video cameras (first, close the lane; wait until no car remains in it; then open it in the opposite direction).

(See Highway Traffic)

The purpose of this measure is to increase the capacity of an arterial and improve safety. It is usually applied to recurring gridlock on an expressway or motorway that experiences stop-start traffic flow and sudden stops that cause accidents. The measure works by imposing or recommending a driving speed:

• in heavy but smooth traffic flows, the average flow speed
• during periods of congestion, increasingly slower speeds from upstream to downstream, to gradually slow vehicles entering the traffic jam area

Speed control systems have been more popular in Europe than in the US or Japan and the major benefit relates to traffic smoothing, with improved throughput and a reduced rate of accidents. Displayed speeds (generally mandatory) are aimed at reducing the range of individual speeds in non-congested situations and protecting the end of queues when congestion appears. The benefits of speed control systems include: smoother flowing of traffic, yielding slightly increased capacity, thus resulting in a postponed disruption time, and reduced number of accidents, especially rear-end accidents. These benefits are obtained through an effective reduction of observed speeds but also through an increase in driver attention.

This measure requires:

• consistent and sufficiently dense data gathering (flow rates, speeds and occupancy rates by lane)
• a high-performance algorithm
• variable message signs at intervals allowing a continuous vision of the signs
• consistent information initiatives (local information campaign to explain the operation, periodic reminders of instructions)

Traffic monitoring is indispensable: the operation is fully automated but an operator must be able to recover control at any time if an unexpected event occurs on the network (such as an accident or sudden deterioration in weather conditions). This measure essentially applies to urban ring roads, where the high proportion of routine drivers facilitates user compliance with operations and the short length of controlled roadway (typically about 10 kilometres) promotes adherence to speed limits.

Apart from handling recurring periods of gridlock, speed regulation is a tool that can be used to gradually slow vehicles entering an incident or accident area.

In some systems (for example, in UK on the motorway around London and Birmingham), the variable speed limit display is coupled with an automated enforcement system (involving video cameras recording licence plate numbers), which issues citations to motorists exceeding the posted speed limit by a predetermined threshold.

(See Speed management)

Although different from the previous methods the control of commercial vehicles, especially freight vehicles, can be an important part of traffic control.  A freight control system will typically use GPS and a mobile phone system to manage the exact location of a vehicle and its freight at any given time.  By extending this system, it can help to control the traffic by routeing the freight to a less congested route. (See  Freight & Delivery Operations)

Driving difficulties for trucks and HGVs during snow for example, may lead to traffic congestion on the whole network. A solution to this situation may be to organise HGVs in convoys. This type of action requires:

• preparation work for selecting the appropriate safe parking zones for trucks and HGVs
• close co-operation with police forces for stopping the HGVs
• organising the convoys and escorting them
• good communications plan to provide driver information

Incident management is defined as the implementation of a systematic, planned and coordinated set of responsive actions and resources to prevent accidents in potentially dangerous situations and to handle incidents safely and quickly. It proceeds through a cycle of several phases: from incident detection to restoration of normal traffic conditions, including the use of immediate and advance notice of possible dangers or problems, such as warnings, in order to prevent accidents.  Incident warning and management have two main goals:

• to prevent or minimise the risk of incidents or the consequences of incidents
• to manage and resolve incidents in a safe, effective and expeditious way regarding the following three aspects in order of priority as follows: safety, mobility of traffic flow and control and repair of damage

(See Traffic Incidents)

This measure consists of spreading out traffic flows over time and space during heavy traffic periods such as long weekends or special national events, causing heavy traffic on a specific arterial or in a particular area. The principle is based on dissemination of information:

• before the heavy traffic period – forecasts for problem times and area
• during the heavy traffic period – information on current traffic conditions

These operations require:

• reliable traffic forecasts
• close monitoring of traffic conditions along all parallel routes or throughout the area in question
• real-time information and publicity tools for media (press kits) and users (maps, calendars, leaflets, website)

The documents distributed must always be up to date and occasionally must be in several languages. It is difficult to assess:

• before the fact, the proportion of users who will follow recommendations
• after the fact, the quality of traffic forecasts and the rate of compliance with recommendations

(See  Planned Events)

Three different approaches are used with this measure, which makes use of Variable Message Signs:

• a ”mandatory” approach, using variable directional signs
• an “advisory” approach, using messages advising drivers to use a given route
• travel time information on competing routes for a given destination, without any advice

Most systems are manually operated with the operator being aided by computer outputs such as travel times on the competing routes, or simply by other data from the field (such as video images), or by pre-determined strategies and traffic management plans designed off-line for a given number of situations. These systems can not generally handle complex situations such as incidents in a grid motorway network, multiple incidents situations, etc and are often unable to give an updated strategy, once the first one is implemented. They also generally do not include forecasts of the demand and of the impact of the current strategy, so they are far from producing an “optimal” strategy, and they can even produce situations worse than a “do-nothing” strategy (due to risk of creating over-diversion).

Some more advanced systems, such as MOLA (UK) or VISUM-online (Germany), are able to simulate the impact of a set of possible strategies designed off-line in order to help the operator to choose the best one.

One system, OPERA (France), is able to automatically generate guidance strategies based on forecasts and on a real-time expert system, thus adjusting itself to current traffic patterns and their forecasts.

Another “collective route guidance” system, in the sense that it induces changes in the users’ route choice is worth quoting: the adjustment of toll rates on competing inter-urban motorways in France during rush hour periods in order to achieve a better balance of traffic.

With this approach route guidance is provided to the individual user at each choice point by means of Satellite navigation which is adapted by an in-vehicle equipment receiving dynamic traffic data. The optimal route can either be calculated on-board on the basis of received data (generally link travel times) using a one-way area broadcast link or calculated centrally and downloaded to the equipment using a two-way short range link. (See  In-vehicle Systems and In-vehicle Systems )

The purpose of this approach is to remove all traffic (or a single category of vehicles) from a road temporarily, in one direction or both. The measure is used following a current, planned or anticipated event that makes it impossible or especially hazardous to travel over the section of road in question. Access to the closed section is prevented via a physical barrier and in most cases, traffic is re-routed. Depending on the circumstances, the closure and detour may be:

• prepared in detail for a specific event (roadwork, popular event)
• prepared generically, as part of a traffic management plan for example (area at risk, high-traffic arterial, problem identified in advance)
• improvised, which is undesirable but sometimes unavoidable

In the case of a prepared closure, implementation follows several stages:

• prepare and check the detour route
• mark the detour route
• inform users and services
• install signing at the closure point and detour entry point
• monitor traffic flow into the detour route
• monitor the signing

The closure of a road is a major operation that mobilises many resources: police forces, temporary signing, communications, control centre or at least a management structure. This measure imposes serious restrictions on the travelling public and services and may entail difficulties for some vehicle categories based on the limitations of the alternate route. The following should be noted:

• if one side of a divided highway is closed the solution of transferring traffic to the other side is usually preferable if opposing traffic allows it, although implementation may require more time
• if the closure is temporary, choice should be made between diversion and holding vehicles upstream from the closure point and releasing them once travel over the section can resume
• if the closure is for a fairly long period (damaged structure or flooding, for example), special measures must be taken for residents along the closed section and to physically block access to the hazardous section

The diversionary routes must be included in the global strategic management of the network using similar roadways or motorways for long distance traffic or local roads for short distance.

A clear distinction must be made between closure of access and regulated access:

• closure denies access for a fairly long period and users are encouraged to choose another route
• regulated access holds users back for a short time but they are allowed to enter the regulated road; some strategies admit vehicles in groups, others allow only one vehicle at a time

Closing access consists of closing one or more access points to a divided highway that is subject to gridlock or closure following an accident for example, while ensuring that alternative routes allow users to complete their travel. The objective is to keep traffic on the roadway below a set threshold to maintain a smooth flow.

This measure can prove effective during peak weekend traffic or heavy travel on connecting highways or when random events reduce the capacity of a roadway to a level below demand. Implementation involves the following key points:

• concerted action under a traffic management plan and technical preparation (advance installation of masked signs or variable message signs)
• use of appropriate control and coordination devices
• signs and physical barriers in place
• devices for monitoring the gridlocked road and alternate routes

For planned and predictable operations an advance information campaign on likely closures and proper signing on-site can strongly influence user acceptance of the operation and thus attainment of the objective. This measure can entail some drawbacks:

• difficulty in closing some sites due to their geometry, status or their various traffic flows
• deterioration of traffic conditions on alternate routes (requiring implementation of specific monitoring measures and/or regulating measures on these routes)
• extent of human resources required on site
• problems communicating with elected officials in neighbouring communities

For reasons of credibility and to avoid shifting traffic from one access point to the next, several consecutive access points may have to be closed simultaneously.

The purpose of this approach is to maintain a smooth flow on a through section or convergence point of a major arterial that is subject to recurring gridlock, by regulating traffic inflow from an access ramp. The objective is to optimise the flow on the major arterial. This type of operation is essentially used on urban highways, but the principle can also be applied in adapted form to intercity highways during periods of heavy traffic.

An information campaign and very accurate technical monitoring are indispensable to user acceptance and credibility of devices. This measure poses certain constraints:

• need for high-calibre engineering to conduct feasibility and impact studies and to define technical implementation conditions
• difficulties convincing local officials and users of the justification for the operation (obvious inconvenience but less obvious benefits)
• extremely limited room for error (massive and ongoing public rejection in the event of dysfunction)

Regulated access is extremely common in the United States and is growing in Europe. There are also a few types of static regulation; on the ring road around Paris, for example, the width of some entrance lanes has been narrowed by small beacons.

Where traffic problems arise on one of two normally concurrent routes (same origin, same destination, similar travel times), it may be effective at some point to direct all traffic to the route with better traffic conditions at that specific time. The principle consists of directing traffic for the destination to the route with better traffic conditions.

Traffic conditions must be monitored on both routes (traffic, construction and local events) and established guidelines must be followed.

Implementation is based on:

• adequate data gathering to assess traffic conditions on both roads
• traditional directional signing, variable at the decision point but constant on each of the two routes
• staff mobilisation at the traffic management centre to ensure consistent management
• ultimately, staff mobilisation to move signs at the decision point

The potential for using this measure is very limited since truly concurrent routes are very uncommon. The impact is limited to through traffic, since local users rarely refer to directional signs; the effectiveness of this measure therefore depends on the traffic mix (local/through).

The purpose of this approach is to avoid gridlock of a section or area that is difficult to manage or poses a hazard if a traffic queue develops. Traffic entering the problem section is limited. This measure is generally used in the following cases:

• a route on which traffic queues must be avoided to facilitate emergency intervention (especially winter service)
• winter access to mountain valleys (risk of trapping users in adverse conditions)
• access to a sports or cultural events or a tourist area with no parking facilities
• hazardous area in which traffic must not be allowed to accumulate (technological or natural risks)

The operation is usually carried out under a traffic management plan (co-ordinated among partners) and in all cases under the operational control of a co-ordinating structure. Traffic is screened at a suitable location (usually a toll booth or intersection, but occasionally in the middle of a roadway equipped with flow control signals to handle the conditions) and adjusted based on traffic conditions in the area to be protected. (See Traffic Management Plans)

Special efforts are made to inform users at the site and extensively upstream. The vehicle holding area must provide adequate capacity, safety and comfort. The tail of the traffic congestion should be marked. Provision must always be made for emergency vehicles.

In some cases, this type of measure may only apply to selected vehicle categories. When faced with major problems, operators may organise several levels of control, implemented in a cascade as a holding area approaches full capacity. Some drawbacks or constraints may appear:

• difficulty convincing users and some operators of the operation’s legitimacy
• potential number of staff required, especially to monitor an area to be protected
• occasionally needless penalisation of some users.

This procedure removes HGVs from a problem area (snow-covered section of road with steep grades or high wind areas, for example) by temporarily holding them in specified areas provided for this purpose. This measure can:

• improve the effectiveness of snow-clearing or salting
• reduce the time required to restore normal conditions
• minimise disruption of the local economy

The measure is implemented in the following stages:

• survey holding areas with minimum facilities compatible with the planned length of the stoppage
• convince authorities of the need for the measure even if the disruption is located outside their jurisdiction
• have the coordinating authority introduce regulations requiring heavy trucks to use the holding areas for a specified period
• ensure police forces are available to direct HGVs to holding areas until the restriction is lifted
• have the measure applied by all players for the full time required;
• have corresponding information broadcast by all media (such as radio, VMS, Internet)

This operation is often associated with measures to assemble trucks into convoys. Some problems can arise and include:

• obtaining the agreement of various authorities when many operators are involved (often the case) and when traffic must be held back in an area unaffected by the disruption
• convincing users and especially drivers of HGVs of the validity of the measure, especially when traffic is held far or even very far from the disruption area

Advance, repeated explanatory media messages to associations representing professional drivers are important (annually, at the start of winter, for example).

The purpose of this approach is to promote anticipation of changes in direction and avoid hesitancy, excessively slow speeds and emergency manoeuvres that cause braking and insecurity, by making signs visible, legible, continuous, consistent and understandable by all. Recurring braking and traffic congestion at an intersection or diverging or merging roads cannot always be attributed to inadequate capacity, but may result from inadequate route guidance. Clarification of signs is implemented in several stages:

• verification of compliance with rules on use of signals, installation of signs and application of markings
• establishment of compliance
• analysis of driver reaction
• carry out improvements

While the system operator is in fact qualified to verify compliance of signs with rules governing use and installation, the same is not true for understanding the causes of driver behaviour; it is important that this part of the analysis rely on people with no knowledge of the local area or traffic-related occupations.

The purpose of this approach is to improve the organisation of traffic by permanently or temporarily changing and enforcing traffic rules. This measure handles braking or traffic jams attributable to poor organisation of traffic, such as intrusive parking, disruptive movements, inconsistent traffic mix, weekly events. This measure is implemented through the following actions:

• clearly identify the cause of the problem (where, when, why?)
• define with all partners involved the appropriate measure to be introduced or enforced
• have the appropriate authority introduce a regulation
• inform users as extensively as possible that the new rules are more restrictive, while clearly highlighting the expected benefits
• install or check the corresponding signs for condition
• enforce regulations (potential use of police forces)

In some cases, compliance with (and effectiveness of) regulatory measures can only be achieved if accompanied by a minimum level of infrastructure changes (such as provision of parking, physical closures, new access routes or -turn lanes).

Many traffic jams and slow moving traffic are linked to a temporary deficit in capacity (intersection gridlocked with returning traffic at the end of a weekend, for example). The purpose of this measure is to restore capacity to the same level as on the rest of the route by making temporary, low-cost improvements to geometry to cope with peak traffic flows or solve chronic dysfunctions. The sites affected are usually intersections and corrective measures include:

• A temporary operation on a major arterial;
• A measure to complement a broader action (introduction of a recommended alternate route, for example).

This operation includes the following steps:

• Analysing problems, such as:
  • too few holding lanes (at a stop or yield sign, at the approach to a roundabout, or at a signal controlled junction)
  • congestion linked to the lack or inadequacy of a holding area ( turn lane, for example)
  • excessively restricted clearance for some manoeuvres (especially for heavy trucks)
  • poor visibility at an intersection
• Gathering traffic data (may include origin/destination surveys)
• Studying and developing a proposal
• Reworking geometry and/or signs
• Confirmation that the problem has been eliminated

Traffic flow must be monitored over the full length of a route (one bottleneck may conceal another) and safety must be maintained (avoid promoting higher speeds).

Beyond the limited improvements noted here, more extensive changes to the geometry of some critical intersections can sometimes be considered (layout of roundabouts, signal controlled junctions, overpass installation); these extend beyond the actual scope of operations and the discussion here.

Road users will consider the quality of the roads dependent upon a range of factors related to how easy, safe and convenient the network is to use. It should be noted that some of these factors will be counter to those seen as important by those living and working close to roads and also may be counter to the desires and aspirations of the road administrations. General indicators applicable to all road users include the following factors:

• delay to travel time along each link in AM, PM and off-peak conditions
• maintenance delays (for example days when there are traffic lane closures)
• accident rates
• security of transport system
• developing countries – travel time and load capacity

These factors will require a consistent measurement approach so that statistics can be compared over time. For example, it will be necessary to define how the delays are to be calculated for each road or category of road, and possibly also different categories of user, and then the measurements necessary to statistically demonstrate the level of delays.

Drivers

Additional factors, which are only relevant to drivers as road users, include signs, information provision, rescue service provision, rescue service operation, and particularly the speed of response to incidents. In developing countries, vehicle wear and tear is relevant.

These factors can be measured by items such as cleanliness and damage repair as well as factors associated with continuity of signs. Again, it will be necessary to evaluate how these factors are to be measured and what indicators are relevant. Some of these factors may be proxy measures; such as the number of times signs are cleaned or checked for obscuration by vegetation. The detection of incidents and speed of response to incidents is a very important factor in the operation of roads, which should be included and again it will be necessary to consider how these effects can most effectively be measured.

(See  Performance Measures)

Passengers

There are a number of factors, that are relevant only to public transport passengers. These include:

• timetable information
• real time information
• service reliability (where related to road conditions)
• crime (real and perceived) on the network
• developing countries – service frequency, seat availability and fare cost

In addition, where the total transport system is being assessed it will be important to include the quality of the service being offered in the public transport area. This will include factors such as:

• ridership
• frequency of service
• coverage of service (eg bus stops related to population)
• service reliability

Measures in this area will also relate to accuracy of information, its availability and type of media.

(See  Passenger Transport Operations)

Freight

Factors which are relevant only to freight users include:

• Access to premises for deliveries
• Freight traffic volumes
• Payload capacity
• Customs and border controls

(See  Freight & Delivery Operations)

The requirements for the wider community are mostly covered by the users and operators requirements. Nevertheless, there are a few additional factors which need to be considered. These relate primarily to the environment and the effect that roads and road operations may have on the environment.

It must also be remembered that some factors are not related to travellers, but affect those who live and work near roads such as:

• noise
• environment
• speed of traffic

Some of these factors can be directly measured, but many are of a subjective nature and can only be qualitatively assessed. Ease of use of the network must also be considered. These include factors such as:

• quality of information for users
• quality of infrastructure
• quality of public transport stops
• pedestrian crossing facilities

Society/network effects

The road user is not the only section of society affected by road quality. Society as a whole has an interest in such matters. In this area, there are a number of network factors that affect society as a whole. These include:

• Pollution
• Safety
• Accessibility and mobility
• Economic costs

These effects may need to be measured for different classes of road, and possibly classes of vehicle. The effects on pedestrians and other road users must be particularly considered in this sector. Again, the factors are often interrelated. A rise (real or perceived) in road hazards may decrease the level of pedestrian activity, thus contribution to the isolation of some communities and reducing their mobility. It is important to consider how these factors can be best measured and particularly to ensure that the measures selected can be repeated over time and do genuinely reflect the changes in quality of the road network and not other external factors.

Surveys of perceived quality may be very important in this area. These will aim to cover user and society effects and can show how the operator is perceived to have addressed (or failed to address) the transport situation. It should be noted that this might indicate a divergence between the perceived and actual performance, which could point to a failure of public relations rather than a failure of the direct operations.

It should be noted that these factors also affect individuals living and working near roads. The measurement of many of the factors in this area may require the use of indirect factors and may be difficult to divorce from external factors such as weather conditions. It will be important to ensure that any measures chosen do accurately reflect the road conditions and not simply other external conditions.

There are a number of factors that relate only to the task of the operator in maintaining the network that do not have a direct impact on the user, except indirectly. These must also be considered when assessing the operation of the network.

These criteria include, again in no particular order:

• safety and security of road network operators and maintenance staff
• cost of operations
• structural integrity
• life of structures
• response to incidents
• level of traffic handled

These factors need to be added to those required to assess the users requirements to give an overall assessment of the performance of the network operation.

(See Asset Management and Planning and Reporting )