In January 1978 TRRL completed the installation of ten sets of vehicle speed measuring and recording equipment on a 19 kilometre section of the northbound carriageway of the M1 between junctions 10 and 13 in Bedfordshire. This report contains average speeds and flows measured during 1978 and 1979. The average daily flow varied from 38,000 vehicles per day in the southern section to 32,000 in the north. On an average weekday about 31 per cent of vehicles travel in the nearside lane, 38 per cent in the centre lane and 31 per cent in the offside lane. Average speeds were 106 km/h (66 mile/h) for short vehicles and 86.5 km/h (54 mile/h) for long vehicles. A speed flow relationship was measured showing a reduction in average speed of 2.9 km/h (1.8 mile/h) for each increase in flow of 1000 vehicles per hour. There were a total of about 220 incidents in each year when signals were set for at least 10 minutes, of which about one-third were accidents, one-quarter visibility, and the rest mainly roadworks, breakdown and shed loads. (A)

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