The effect on vehicle speed of advisory speed indications shown on motorway signals has been measured at two sites on the M1 motorway. On an urban section of the motorway at Scratchwood in n London, measurements were made of vehicle speeds before and after a set of signals mounted over the carriageway on a gantry. The signals were set to show an advisory speed of 50 mile/h. Control measurements were also made with the signals switched off. The average speed of light vehicles in the right-hand lane was reduced from about 78 mile/h to 71 mile/h (9 per cent); in the centre lane from about 69 to 63 mile/h (7.5 per cent); and in the left-hand lane from about 57 to 55 mile/h (4 per cent). similar measurements were made on a rural section of the motorway at Newport Pagnell where the single signals are mounted on posts in the central reservation. The average speeds of light vehicles in the right-hand lane was reduced from about 77 mile/h to 69.5 mile/h (9.5 per cent); in the centre lane from about 68 to 63 mile/h (7 per cent); and in the left-hand lane from about 55 to 52 mile/h (5 per cent). at both sites downstream from the measurement sections, the fast lane was closed for maintenance work. Drivers could not see the temporary signing or the closed lane from the measurement sections, so the speed changes measured would be in response to the signal indications. (Author/publisher)
Abstract