Estimating the cost of conversion of road traffic signs to metric units

Estimating the cost of conversion of road traffic signs for speed and distance measurements to metric units

1. A short exercise was carried out to provide a broad indication of what it would cost to convert speed and distance measurements on traffic signs to metric units, if such a change were to be made.

Costs of changing signs

Works costs

2. Estimates for the number of signs of different types were derived from a study carried out in the early 1990s to develop a methodology for compiling a traffic signs inventory. Since that time the increased attention given to speed management, e.g. 20mph zones and speed restrictions as part of road safety schemes, will have increased the number of speed limit signs. There have also been increases in the number of traffic calming schemes which often include distance measurements, (e.g. humps for x yards) and the number of direction signs, especially the brown and white tourist signs, again including distances. Pedestrian signs with distances are also thought to have increased in city centres. The original estimates were therefore increased for specific categories of signs and for a general increase - the latter taken as 10%. The original study had made estimates for England only. As the whole UK would be affected by conversion, the estimates were factored in proportion to the additional urban roads in the other countries, to reflect the fact that most signs are likely to be in urban areas. Overall, around ½ million signs could be affected.

3. Rates for carrying out the necessary works that would be needed to replace signs were obtained from the Highways Agency, a local highway authority and sign manufacturers. Account was taken of the size of signs and whether they would need to be replaced completely or the relevant part of the sign could be plated. The latter would generally only suitable if there was a simple distance to be changed, e.g. on the "1m" marker on direction signs approaching a motorway junction. The table of estimated costs is at Annex A, including the main assumptions. After allowing for preparation and supervision, design of the sign faces and for optimism bias, in line with standard estimating procedures, the overall cost of changing the signs is estimated at around £560 - 640m.

4. One of the key assumptions was that the motorway and major road advance direction signs, which are large and in some cases mounted on gantries, would just have the "½m or 1m" plated over with a metric equivalent. A more consistent approach to metrication could be to relocate these signs to 1km or 2km positions. This would be very costly, and in some cases may be impossible because of road layout constraints. It would add very substantially to the costs - affecting not only structural matters such as foundations and redesigned gantries but also involving new communication connections, road closures and major traffic management. These costs have not been included at this stage.

Preparatory work

5. The costs described above relate to the works that would be involved in changing the signs. Preparatory work would be needed:

(a) to survey the existing signs to see which ones need changing. This would require on site surveys;

(b) for distance signs, to decide what the new distances should be;

(c) for speed limits, to review the speed limits, matching them against the new metric limits. This would not be a simple exercise. Conversion would inevitably create new options and authorities would need to reconsider what new limits were appropriate where on their networks;

(d) to review and revise as necessary any speed limit orders.

Assuming £0.5m for each of the 208 UK traffic authorities (local and national) to cover this work would amount to around £100m.


6. Publicity would be needed for the lead in and surrounding conversion to ensure a smooth transition, this would need to be co-ordinated between central and local Government. Allow £10 - 15m.

Project management

7. This would all need careful planning and co-ordination as a major project in its own right. Allow project management costs for Government and consultants of £10m.

Overall costs of changing signs

8. Table below

Works 560 - 640
Preparatory work 100
Publicity 10 - 15
Project management 10
Total 680 - 760 ( around 1 - 1.1 bn Euros )

Other costs

Cost to businesses and other organisations

9. There would inevitably be costs to businesses of changing elements of their processes to operate in metric e.g. mileage based delivering costs, mileage allowances. These could be very widespread, including changing computer systems, desk instructions, stationery, directions on publicity material etc. With 1.6m VAT registered businesses in UK, even small costs per business could mount up to very substantial sums. For example costs of say £100 - £200 on average per business would amount to £200 - £300m overall. Similar types of costs would affect public sector organisations and the voluntary sector. Again even relatively small costs for individual organisations would mount up to significant totals overall.

Driving related publications

10. Driving manuals such as those produced by DSA and other training material would need to be revamped to refer to metric units. Map publishers would need to recalculate all the distances marked on their maps to change them to kilometres. Costs would be incurred, although these might be recovered through higher prices for the products and services.

Traffic Management Division
November 2005

Annex A
Assumptions for costs of changing signs

  • Large signs plated, not replaced (e.g. ADS with distance to junction shown as 1/2m or 1m).
  • Route confirmatory signs replaced, as conversion of miles to kilometres and addition of km would occupy more width than could be accommodated on a plate.
  • All small signs, such as distance plates (e.g. "250 yds", or "For 2 miles") replaced.
  • Height restrictions on triangular warning signs and width, height or length restrictions on circular signs replaced
  • No allowance made for replacing temporary road works signs as these assumed to have a short life and therefore converted in course of normal replacement
  • No double handling or storage of signs
  • No premium rate used for works being completed in "1 week"
  • Rates based on 8 hour shift
  • Day time working - for small signs only. Night shift for large/ motorway signs work
  • Range of optimism bias for outline estimate from 45%, typical for a standard scheme, to 65% for non standard scheme
  • Works costs do not include VAT

Costs not included

  • Moving underground services if posts have to be moved
  • Replacing sign lighting
  • Repairing road surfacing where markings removed
  • Delays to traffic caused by works

Cost summary

Costs from Table below (England only) 241
Extra 10% for number of signs increased 24
Disposal costs @ £10 per sq m 4
(Total) 269
Plus extra 16% for rest of UK 312
Plus supervision, preparation & design @ 25% 390
Plus optimism bias @ 45 - 65% 565 - 644
Total 565 - 644

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