Highway safety inspection policy
Defect risk assessment
The principles of a system of defect risk assessment for application to safety inspections are set out below. Any item with a defect level which corresponds to, or is in excess of, the Minimum Recording Level is to be assessed using the risk assessment matrix.
Risk impact
The impact of a risk occurring is assessed as follows:
- minor or low impact
- noticeable or medium impact
- high or serious impact
- very high or severe impact
The impact is quantified by assessing the extent of damage likely to be caused should the risk be realised. The main consideration of impact is the severity of the defect. However, other variables such as road speed and nature of traffic may also affect the likely impact.
Risk probability
The probability of a risk occurring is assessed as follows:
- low probability
- medium probability
- high probability
- very high probability
The probability is quantified by assessing the likelihood of users, passing by or over the defect, encountering the risk. As the probability is likely to increase with increasing vehicular or pedestrian flow, the network hierarchy and defect location are important considerations in the assessment.
Risk factor
The risk factor for a particular risk is:
Risk factor = risk impact x risk probability
It is this factor that identifies the overall seriousness of the risk and consequently the appropriateness of the speed of response to remedy the defect.
Risk management
Having identified a particular risk, assessed its likely impact and probability and calculated the risk factor, the category and the timescale to rectify the defect is either defined as an Emergency response, Category 1 response or allocated to one of the Category 2 defect types (low, medium or high).
The risk matrix below, whilst not prescriptive, helps the inspector to assign the appropriate classification of defects when considering impact/severity against probability. This matrix is again based upon similar matrices employed by other highway authorities and general good practice for risk assessment, see Table 5.
| Impact severity | Low probability (1) | Medium probability (2) | High probability (3) | Very High probability (4) |
|---|---|---|---|---|
Minor |
Cat 2L |
Cat 2L |
Cat 2L |
Cat 2L |
Low (1) |
Cat 2L (1) |
Cat 2L (2) |
Cat 2M (3) |
Cat 2M (4) |
Medium (2) |
Cat 2L (2) |
Cat 2M (4) |
Cat 2H (6) |
Cat 2H (8) |
High (3) |
Cat 2M (3) |
Cat 2H (6) |
Cat 1 (9) |
Cat 1 (12) |
Very high (4) |
Cat 2M (4) |
Cat 2H (8) |
Cat 1 (12) |
Emergency (16) |
Emergency |
Emergency |
Emergency |
Emergency |
Emergency |
| Score | Category |
|---|---|
Score of 1 to 2 |
Cat 2L |
Score of 3 to 4 |
Cat 2M |
Score of 6 to 8 |
Cat 2H |
Score of 9 to 12 |
Cat 1 |
Score of over 12 |
Emergency |
The inspector may determine that a defect is very minor or extremely dangerous at the time of assessment and place the defect in either the Minor or Emergency impact/severity category as appropriate.
Scoring does not apply to defects within Minor or Emergency impact/severity.
Probability
Probability is the inspector’s assessment of likelihood of the defect affecting the safe passage of vehicles, cyclists and pedestrians along the highway or affecting the structural integrity of the highway. It follows an assessment of the road Hierarchy and the location of the defect within the road.
Impact and severity
The impact/severity is quantified by assessing the extent of damage likely to be caused should the risk be realised. The main consideration of impact/severity is the magnitude or dimension of the defect. However, other variables such as road speed may also affect the likely impact.
Failed roads
In certain circumstances, some roads may contain so many defects that it is impractical to undertake permanent localised repairs. Defects will be made safe in accordance with this policy, but, and at the discretion of the Highways Community Liaison Manager, action may be taken such as the erection of “Failed Road” warning signs to warn drivers to proceed with caution. The use of Failed Road warning signs must be recorded (location and duration) and periodic inspection of the warning signs instigated by the Highways Community Liaison Manager until the road has undergone planned maintenance. These roads should be considered for more permanent repairs in line with the Asset Management policy and strategy.
Minimum recording levels
It is recognised that in WMHI these are referred to as minimum investigatory levels, but BC consider the use of the phrase “minimum recording levels” to be more appropriate for the management of defects on its network. Minimum Recording Levels are based on recommendations contained within WMHI and BC’s general and historic experience that they are at least sufficient for their respective defect types.
It is also recognised that on any highway network, a multitude of minor defects will exist which do not pose any risk to either the safety or the integrity of the highway. Any defects which do not meet the Minimum Recording Levels (as defined within Appendix A) will only be recorded should the Inspector deem this appropriate (for example, where a cluster of such defects may form a potential preventative maintenance scheme in the future). Where such defects are recorded, they will be recorded as Cat 2L defects.
All defects which reach minimum recording levels will be assessed and recorded in line with this policy, but intervention and repair will only take place if required in accordance with the risk assessment process set out above.