This paper presents a case study of a low- radius curve on a major urban road which demonstrates the inadequacy of current geometrical design criteria. The road studied, Broad Lane, is a length of the A503 in Tottenham, North London. It is part of a large one-way system at the intersection of the A10 trunk road with the A503. The area is densely populated. Broad Lane consists of a 300m long straight, a 28m radius curve and another straight of about 500m. It is three lanes wide. The operating speed of the curve has been measured to lie within the range 17 to 48kph, mean value - 31kph. The personal injury accident record for a 3.5 year period shows 5 events, one of which could not be attributed to the curve. There is no substantial evidence that non-personal injury accidents occur frequently. Design standards of the Department of Transport are based upon the criterion that lateral acceleration should not exceed 0.22g. Speed measurements at broad lane indicate that 75% of drivers choose to adopt speeds generating more than 0.22g. It is suggested that a more appropriate criterion would be 0.40g for roads subject to a 50kph speed limit.
Abstract