Case Study

Norfolk Interactive Fibre Optic Signs

Speed Activated Sign, Photo courtesy Centaur Consulting.Tools Involved

  • Vehicle Activated Signs

Site Description

Much of Norfolk's road network is made up of rural routes. Since 1992 Norfolk Council has trialled signing techniques to persuade drivers to slow down, be aware of potential hazards and not to travel on unsuitable roads.

Site Problems

Inappropriate and excessive speeds on rural roads are often a contributory factor in road traffic accidents. Fixed signing can be supplemented by interactive signs to increase the overall signing impact.

Scheme Description

The Interactive fibre optic signs use two methods for speed detection. On roads of above 40mph inductive loops are placed in the road 150m before the sign (this is generally used where the risk of accident and severity is high). On roads of speeds below 40mph, 'radar speed discrimination detectors' are placed on top of signs to measure the speed of approaching vehicles. In both methods, if the approaching vehicle exceeds the pre-defined threshold (normally 5mph above the limit) the sign's fibre-optics are illuminated (normally for a period of 4 seconds).

The signs display a variety of displays including:

  • 'slow down' messages;
  • the speed limit of the road;
  • a warning of an approaching junction;
  • a warning of an approaching corner; and
  • discouragement from using a specific lane.

Scheme Objectives

The main objective of interactive signs is to gain the motorist's attention, make them more attentive and, where appropriate encourage them to slow down. Fixed signs can sometimes go unnoticed, but because the signs respond to individual drivers it makes them far more visible.

Improvements

It is anticipated that the system will:

  • reduce speed;
  • reduce accidents; and
  • improve driver awareness.

Integrated Systems

The speed measurements can be stored in a database to determine the effect of the signs over time and calculate the average speed.

Costs

Capital costs: approximately £6,000 per sign
Revenue costs: approximately £240 per sign per year


Benefits

Benefits are shown in the table below.

Actual benefits reported
Impact Assessment Environment No benefits expected or reported.
Accessibility No benefits expected or reported.
Safety Average reduction in speed of 4.3mph. National Research has shown a drop in 1mph equates to 5% reduction in accidents, so on average there is a potential reduction in accidents of 21.5%. At 21 sites, there were one third less injury accidents overall.
Efficiency No benefits expected or reported.
Integration No benefits expected or reported.
Technical Performance No technical problems reported.
User Acceptance Several sites in Norfolk were surveyed, with over 90% of users thinking the signs were a good idea.

Norfolk Interactive Fibre Optic Signs benefits table

(source: Vehicle Activated Signs - A Large Scale Evaluation - M A Winnett and A H Wheeler 2003, TRL Report TRL548, http://www.trl.co.uk/online_store/reports_publications/trl_reports/cat_vehicle_engineering/report_vehicle-activated_signs_-_a_large_scale_evaluation.htm) The report is available for free for those who register.

No attempt has been made to validate the results reported. Users of the guidance are encouraged to assess the robustness of the results presented and the likely transferability of the case study to their own local environment.