§ Mr. PawseyTo ask the Secretary of State for Transport what is the design capacity of the M1 from junction 1 to Luton; and what is the current traffic flow for the hours of 7 am to 10 am and 4 pm to 7 pm. [4099]
§ Mr. WattsI have asked the chief executive of the Highways Agency to write to my hon.Friend.
56WLetter from Laurie Haynes to Mr. James Pawsey, dated 25 November 1996:
The Secretary of State for Transport has asked me to reply to your recent question about design capacity and traffic flows on the M1 between Junction 1 and Luton (Junction 10).Between M1 Junction 1 and 10, certain lengths of the motorway are much busier than others. Traffic counts on motorways are carried out junction to junction. Data for one small section of this length of the M1 (Junctions 6-6a) are not currently available. Between Junctions 1 and 10 the average flow is therefore the arithmetic mean of traffic for the 8 sections of motorway, but excluding the section between Junction 6 and 6a. The highest recorded flows are between Junctions 7–8 and the lowest flows are between Junctions 1–2. For the three hour periods requested the flows are typically as follows:
Junction Vehicles Southbound 7 am-10 am Vehicles Northbound 7 am-10 am Vehicles Southbound 4 pm-7 pm Vehicles Northbound 4 pm-7 pm Average between Junctions 1–10 13,000 8,900 9,500 13,500 Junction 7–8 (dual 4 lanes) 17,800 14,100 14,600 18,070 Junction 1–2 (dual 3 lanes) 10,000 4,500 5,100 9,100
There is no precise definition of a road's capacity since it is dependent upon a number of factors such as alignment, frequency and type of junctions, volume of traffic entering and leaving at junctions, flow composition eg the proportion of heavy goods vehicles, and the weather. There is a relationship between speed and volume such that as a road get busier speeds reduce. However, at lower speeds flows may not decrease but may even increase with vehicles being able to travel safely more closely together. On motorways, speeds normally start to reduce when the flow increases beyond 1,600 vehicles per lane per hour. During a three hour period this equates to a unidirectional vehicular flow of about 14,400 vehicles on a dual three lane motorway, ie Junction 1 to 2, and 19,200 vehicles on a dual four lane motorway, ie Junction 7 to 8. However, the characteristics of the MI close to London mean that speeds would reduce at lower flows than these.