Dark Matters: de-illumination and road safety

Getting to grips with the facts and figures of LED vs retro-reflective

De-illumination: a business case

TSRGD offers local authorities and asset owners the option to de-illuminate certain signs and bollards, there appear to be obvious savings to be made… but is this at the expense of road safety?

Recent and proposed changes to regulations have reduced the conditions under which illumination of signs and bollards (in certain situations) is mandatory. This relaxation puts the onerous decision-making and associated risk of de-illumination onto the local authority or asset owner. They are left with two immediate choices, to continue to illuminate those signs and bollards where the requirement has been removed or to de-illuminate and use retro-reflective material.

This relaxation has seen a rise in the availability and opportunity for retro reflective bollards – a non illuminated bollard which reflects light incident on its surface to highlight the area of danger and many suppliers of retro-reflective materials for all types of road sign. These products have the attractive benefit of eliminating the ongoing electricity cost altogether. However, there are several other considerations to take into account when making this decision.

Retro-reflective materials do have technical limitations and if not kept clean from dirt, graffiti, and even dew its effectiveness is significantly reduced. Many factors such as positioning, ambient lighting levels and the angle in relation to the observer, amongst others, impact on whether the sign or bollard is clearly visible to a road user during the hours of darkness. Reflective surfaces do not provide an adequate solution for highlighting potential danger areas for pedestrians or cyclists, they also pose an issue for drivers of larger vehicles where they are sat a lot higher than their headlights.

Guidance from the DfT in reference to removing direct lighting states, “it is recommended that robust risk analysis should underpin any decision to do so on a case by case basis”.

An additional note from Traffic signs manual, Chapter 3, states “some signs may be sited where they will not receive adequate illumination from headlamps and it might be prudent to provide direct lighting regardless of the regulatory requirements.”

The Business Case

Local authority budget cuts make it increasingly difficult to maintain existing assets, make use of technological advances and benefit from new product development. There are many options available when it comes to reducing the costs associated with the operation and maintenance of illuminated signs and bollards. This article sets out to understand the areas of operating cost for traditional internally illuminated bollards and signs and considers the business case for use of retro-reflective products compared to LED retrofits of these systems. In doing this, several assumptions have been made; these are listed in the appendix to this article.

In addition safety factors of de-illuminating and the options available to achieve a reduction in costs whilst keeping signs directly illuminated, are considered.

The operating costs associated with a traditional bollard or externally lit sign can be split into the following areas:

  • Energy costs
  • CRC charge (linked to energy usage)
  • Cleaning costs
  • Apportionment of ongoing replacement lamp costs
  • Apportionment of ongoing sign/bollard costs

 Bollards

Internally illuminated bollards comprise of a base, or foundation, and a polymer based ‘top’. The base contains a gear tray and traditionally houses 2 or 3 fluorescent lamps, which can be driven by a magnetic or high frequency ballast. The top is a low cost part of the bollard, which is manufactured in volume. When illuminated, the bollard appears bright and uniform, alerting drivers to an area of potential danger when viewed from all angles.

A bollard top will typically have a 10 year lifespan. After this point the bollard top can be detached from the base and a new bollard top can easily be installed.

The energy consumption is calculated from the power consumption (circuit watts of 30 for 2x11W PL lamps) and the number of hours of operation per year (taken as 4,500 hours for dusk until dawn operation).

As dirt, dust and debris become deposited on the bollard top surface the amount of light transmitted reduces. It is therefore necessary to clean the outer surface of the bollard periodically. The required frequency of cleaning will depend on the local environment, but a typical clean regime would be 1 clean per year.

The apportionment of costs relating to the replacement of lamps and the bollard top are calculated by considering the expected life of the product and the annual usage. An overview of the costs is shown below:

De-illumination Fig1

De-illumination Fig2

Figure 2 shows that costs related to energy, account for 47% of the total operating costs. To drive down costs whilst still maintaining compliance with regulations and safety for road users it is important to target each area of spend individually, starting with electricity use.

RETRO-REFLECTIVE BOLLARDS

Retro-reflective bollards eliminate the costs associated with energy and lamp changes altogether. However, there are significant increases in costs associated with cleaning and the ongoing replacement of bollards following damage.

With an internally illuminated bollard dirt build up will gradually reduce transmission of light through the bollard top. However, the reflective properties of a retro-reflective bollard require the surface to be relatively dirt free. This therefore warrants an increased clean frequency and subsequent maintenance costs in this area. Periodic replacement of the whole bollard will be necessary as the reflective surface degrades (approx 10-12 years). Since the costs of the retro-reflective bollard are significantly higher than the cost of a polymer bollard top, the ongoing replacement costs are higher as well.

It is worth noting that following an incident it can be necessary to replace the bollard, since the reflective surface can become damaged, further increasing costs. From a safety critical point of view, a severe incident can shear the bollard, completely detaching it from the ground. In the case of a retro-reflective bollard this leaves the hazard unmarked altogether, whereas when the bollard top is sheared from the ground the base plate will still be illuminated, performing a similar function to a cat’s eye providing some residual conspicuity.

Figure 3 shows that, while energy costs are eliminated, others are increased significantly:

De-illumination Fig3

The total annual operating cost is reduced by around 33%. However, when considering the high upfront costs of removing or making safe the existing supply and the cost of the new bollard the payback becomes difficult to justify.

 LED RETROFIT BOLLARDS

LED retrofits offer the advantage of relatively low upfront cost while providing benefits of reduced energy consumption. Furthermore, keeping the internally illuminated bollard setup means that there are the additional discussed benefits of visibility and no time or resource needed to complete a detailed risk assessment.

Converting to LED by using a lamp retrofit (compared to gear tray replacements) allows for extremely simple installation while keeping costs low. It also allows the installer to continue to keep two separately fused light sources rather than one, as recommended in the CSS report, this gives the assurance that in the event of a lamp failing there is still some light provided.

Figure 4 shows how overall cost is reduced equating to a saving of over 40%:

De-illumination Fig4

Payback periods across the comparison calculations are summarised in the graph below;

De-illumination Fig4a

Operational revenue savings can be made from de-illuminating and capital investment can support the use of retro-reflective bollards but does this provide an adequate solution for all road users, particularly non-motorised users?

Signs

Retro-reflective signing material provides a comparable level of illumination to direct lighting in many circumstances, however it does not in itself provide sufficient illumination to justify the removal of all lighting and consideration needs to be given to the appropriate method of lighting for each situation.

Full details can be seen in TSRGD, as a summary the conditions under which sign illumination is still a mandatory requirement are;

  • Warning and regulatory signs where headroom is restricted
  • Safety critical regulatory signs
  • Regulatory terminal signs, such as Give Way, No Entry, Speed limits
  • Motorway signs
  • Signs on internally illuminated bollards

Most existing lit signs contain twin fluorescent tubes which can easily be replaced with LED retrofit lamps to reduce the energy consumption and the required maintenance visits to replace lamps. Levels of illumination required for internally or externally lit signs are specified in BS EN 12899-1 and any sign upgrade, or retrofit option considered should be compliant with this standard. Lumen depreciation figures (L80) should also be taken into consideration and accounted for as part of the whole life costing and payback calculations.

The energy consumption of a traditional lit sign is calculated as circuit watts of 15 (for 1 x 11W PL lamps) and the number of hours of operation per year (taken as 4,500 hours for dusk until dawn operation). An overview of the costs is shown below.

De-illumination Fig5

De-illumination Fig6

As with the traditional bollard system, the costs related to energy, account for almost half of the total operating costs of a sign. Electricity along with maintenance costs is a key target area for many local authorities to reduce revenue costs.

RETRO-REFLECTIVE SIGNS

Retro-reflective signs eliminate the costs associated with energy and lamp changes altogether. However, there is a significant increase in costs associated with cleaning and with ongoing replacement following damage.

Safety concerns are raised for drivers of larger vehicles where the headlights are a lot lower than their seated position. Retro-reflective materials are excellent at reflecting light directly back to the vicinity of the light source with a low angle of reflection i.e. which works well for car drivers. However in HGVs, buses and other large vehicles, the levels of light reflected back to the driver are often significantly lower. As with retro-reflective bollards there is little indication of hazards to cyclists or pedestrians.

Figure 7 shows that while energy costs are eliminated others are increased significantly.

De-illumination Fig7

LED RETROFIT SIGNS

LED retrofits offer the advantage of relatively low upfront cost while providing benefits of reduced energy consumption and maintenance. This reduction in operating costs allows local authorities to maintain lit signs without the need for de-illuminating or full sign replacement. Converting to LED by using a lamp retrofit (compared to gear tray replacements) allows for extremely simple installation while keeping costs low.

Figure 8 shows how overall cost is reduced, equating to a saving of over 40%.

De-illumination Fig8

Payback periods across the three comparison calculations are summarised in the graph below;

De-illumination Fig8a

Solar powered, electroluminescent signs and low voltage lighting are all other available options that haven’t been considered as part of this article, however it is assumed that payback periods would be similar to those calculated for retro-reflective product installations.

 Conclusion and Recommendations

De-illumination of any road safety features should be undertaken with caution and the appropriate risk assessments carried out, considering the environment, the usage of the area, impact of dirt and pollution on retro-reflective materials and the overall cost vs benefits

Non-illuminated solutions are viable options to be considered as part of the design risk assessments for new installations. However the calculations show that for existing installations there is no financial benefit to de-illuminate, due to the high upfront cost of changing, and the fact that investment has already been made to provision an electricity supply to the unit.

It has been shown that using an illuminated solution can be the most cost effective solution, and continues to maintain road safety for all users including pedestrians and cyclists and drivers of larger vehicles.

Reference and further reading:
  1. CSS SL5/2007 Guidance on the lighting requirement for traffic signs and bollards (2007)
  2. Traffic Sign Regulations General Directions, 2002, Amendment 2 (2011)
  3. Traffic Signs Manual Chapters 3 and 4
Appendix:  Calculation assumptions
  • Electricity cost £0.12/kWh
  • CRC charge £16.00/tonne CO2
  • Annual burn hours 4500
  • Lamp life of fluorescent 10,000 hours
  • Lamp life of INDO Direct Drive® LED 140,000 hours
  • Clean frequency of traditional bollard 1 per year
  • Clean frequency of retro-reflective bollard 2 per year
  • Clean frequency of traditional sign 0.25 per year
  • Clean frequency of retro-reflective sign 1 per year
  • Life of traditional bollard top – 10 years
  • Life of retro-reflective bollard – 10 years
  • Life of traditional sign – 20 years
  • Life of retro-reflective sign – 10 years