Traffic Incidents and Unplanned Events

Traffic Incident Management (TIM) is the response to traffic accidents, incidents and other unplanned events that occur on the road network, often in potentially dangerous situations. The objective is to handle incidents safely and quickly, to prevent further accidents and restore traffic conditions back to normal as quickly as possible. It requires the deployment of a systematic, planned and coordinated set of response actions and resources.

Traffic Incident Management proceeds through a cycle of phases starting with immediate notice of possible dangers or problems ahead – as soon as an incident occurs – in order to forewarn drivers and prevent accidents.

Incident warning and management have two main goals – to:

• prevent or minimise the risk of incidents and the consequences of incidents
• manage and resolve incidents in a safe, effective and expeditious way

Incident management requires planning, a response that is proportionate, safety at the scene of the incident and recovery. It requires attention to three main aspects – in order of priority – safety, mobility of traffic flow and control and repair of damage.

To understand how control strategies and network operations can reduce the negative impact of incidents, it is important to understand the timeline and different stages of incidents, as shown in the diagram below.

The diagram might represent a collision on a motorway, a spill of materials or a disabled vehicle - resulting in the need to close one or more of the running lanes. All steps will not occur in every incident - and there may be other interwoven relationships – but the diagram represents the typical sequence for most moderate-to-serious incidents. The steps are shown in a staggered fashion simply to illustrate that the incident timeline is not uniform (the time increments are relative – and not to any scale).

The duration of particular stages in the incident are represented by the letter pairs in the diagram and are listed below. For example, the duration of the incident itself would be from point A on the timeline to point M, while the total time the incident is having an effect on traffic is from A to N – with the time elapsed to point N often proportionately much longer than shown.

Common phases of an incident are:

• detection that an incident has occurred: A to B
• verification that the incident has occurred, determining its location and having sufficient information to enable an appropriate response: B to C
• response by dispatching appropriate services to resolve the incident: C to E
• clearance, or the removal of the vehicles, damaged property and victims from the incident scene, and complete reopening of any blocked lanes: E to M – with roadway clearance as a subset, E to K
• recovery to normal traffic flow: M to N

Although not evident in the diagram, the recovery period is frequently longer than the duration of the incident itself. Incident recovery can be four-to-five times longer. This means that for every minute that can be trimmed off incident detection, verification and/or clearance, up to 5 minutes of recovery time can be saved for traffic to get back to normal.

Secondary Incidents

Avoiding secondary incidents is of paramount importance because they start the incident response cycle all over again. The aerial photograph below illustrates this point. The original incident that caused the multiple vehicle pile-up was a car that was stationary due to its engine overheating – which blocked a traffic lane in the direction going “downstream”. The stationary vehicle was the cause of one or two collisions but many more collisions on both sides of the highway occurred because a vehicle responding to the incident attempted to bypass the traffic queue and reach the incident by travelling the wrong way on the opposite side. The example shows that secondary incidents can in fact be more serious than the original incident.

Roles and Responsibilities

All agencies must work closely together to quickly detect an incident, and to verify, respond and clear it in as timely and efficient a manner as possible. ITS in general and the Traffic Control Centres (TCCs) in particular will play a part at each stage. (See Urban Operations and Highway Operations) The emphasis must be on the rigorous application of the 4-Cs of incident management (Communication, Cooperation, Coordination and Consensus) and close inter-agency working, through Traffic Incident Management (TIM) teams. Traffic Incident Management Teams and Safety Service Patrols are vital elements of a good traffic incident management programme. (See Incident Response Plans)

Clarity in assigning roles and responsibilities to the Traffic Incident Management (TIM) Team, the Mobile Safety Service Patrols and tow-truck providers during traffic incidents cannot be understated. Even though the TIM team may not be an active participant in the response to a particular incident, it has a key role to play in formulating the policies, practices and training that go into it. TIM members will include the first-line responders or organisations that provide direct support. Mobile Safety Service patrols and tow providers are also active participants. (See Mobile Patrols)

Typical use of ITS devices and the roles and responsibilities of the TCC and Mobile Safety Service Patrols are summarised in the two tables below for different stages of an incident. In these tables there is no implied sequence of actions within cells – instead they are typical actions that might be taken.

Detection, Verification and Response

Clearance and Recovery

Collision Protection and Safety Management

Protection of personnel and field equipment from vehicle impact is of primary importance during any traffic incident or on-road emergency. Use of high-visibility vests or uniforms by incident response teams and maintenance workers should be mandatory. High-visibility markings on response vehicles and maintenance trucks helps to avoid collisions. Buffer zones around incidents or maintenance work create a safety zone – although care needs to be taken to balance safety with keeping roadway capacity available for traffic flow. Standard practice differs considerably from country to country and local practices should be followed where they exist.

All means of travel and traffic information can be used to provide timely and accurate information to travellers about the nature and location of incidents and maintenance activities (See Travel Information Systems). Automatic Incident Detection can support queue protection warnings to the approaching vehicles up-stream (See Automatic Incident Detection).

Several innovative initiatives have been used in Europe and South America, as follows:

• using an elevated lighting system to illuminate an incident or maintenance scene whilst reducing glare for approaching vehicles
• using portable shields to block public view and reduce “rubbernecking” by drivers on the opposite carriageway slowing down to observe the incident
• using motorcycles with narrow trailers to respond to incident, particularly in restricted facilities like a tunnel or underpass. This can reduces exposure for both responder and motorists, and have even been used to evacuate injured persons from an incident

Responder Safety

Advice to Practitioners