The Incident Support Unit are there to give the initial response to the incident. The first thing they need to do is get to the scene. Incident Support Units and other highway representatives do not have the 'luxury' of blue lights, so their approach to the scene is somewhat slower than the emergency services. They will make there way slowly and carefully along the hard shoulder, firstly to the point of closure, then to the incident (once the officers at the point of closure have assured them that it is safe to proceed).
Travelling the hard shoulder is full of dangers in these circumstances. They will encounter the usual debris in the carriageway, there will be broken down vehicles, there will be the usual idiots who consider that their time is far more valuable than others, so they will pull out from lane 1 onto the hard shoulder without checking that somebody may be coming along it to attend the scene, there will be people who want to nip down the embankment to answer a 'call of nature', there will be people who get out of their car to stretch their legs and have a chat with others about what might be causing the hold up. Therefore, extreme caution is exercised when approaching the point of closure/scene.
Problems could be so severe when attempting to reach the scene that a Police escort is required; if the Police can assist, they will. This is not normally a problem for the Incident Support Units or Supervisors, but it can be a considerable problem for the traffic management vehicles and specialised plant, which are far larger.
At the point of closure it is likely that the Police will have closed the road using a dozen or so 450mm cones from the back of the Police car. Some officers will tell the Incident Support Unit to strengthen the closure by using 1m cones and signing from the sign bins that are situated at many junctions, other officers will tell the crew to proceed to the site where there presence is more urgently required.
It may be that due to extent of injuries a full investigation is required by the Police, and if so, the Police have already started to turn back the traffic that is trapped between the point of closure and the scene. In this situation, the motorists are always instructed to travel in single file slowly and keep to the left (travel in the offside lane.) The situation is the same for the HA representatives, but their "left" is of course the hard shoulder. Again, getting to the actual scene can bring all the dangers as highlighted above, and extreme caution is exercised at all times. People in the queue do get stressed and do silly things in these situations.
Assuming that the Incident Support Unit is the first HA "representative" at the scene (which is often the case), they are there to do any immediate work (clearing of carriageway, making safe) and give the first basic engineering assessment. They will locate the "Officer Dealing", who will log them in with names, organisation and time. They will confirm with the Police what is required of them, and then notify the Network Control Centre of the Police requirements (now that things are probably clearer). The Network Control Centre will then update the Client Supervisor on what is happening at the scene, what is required, what is already en-route, and ETA's of any plant and labour.
The Client Supervisor will know if the diversion route is permanently signed or not and will issue the necessary instructions to the Network Control Centre. He will then contact the Term Maintenance Contractor Supervisor/Agent to order additional resources. This way, he knows what he is ordering is what he's going to get: Network Control Centre operators are not "highways people", they are a call centre, whereas the Client and Term Maintenance Contractor Supervisors/Agents have the required highway knowledge.