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straight crossfall to the west and its centre line is marked only by cat's eye
A tree and adjoining shrubs on the north side partially obstruct
vision of the junction for southbound traffic, Stereophotographs were
obtained from camera stations 1, 2 and 3 in that order, This operation
lasted some twenty minutes but at station 3 (see Fig. 2) the damaged cars
had been cleared off the road, Another difficulty on this occasion was that
the accident team's car was too small for the normal camera tripod and a
smaller tripod had to be used. As a consequence the camera height was
only some 60 per cent of its optimum and its effect in cramping road detail
is clear in the photographs (Fig. 2). Plotting from such photographs is
rather more onerous than usual In this accident the probable positions of
the cars at impact were determined from tyre scrub marks on the road,
debris resulting from the impact and by "fitting" the damaged outline of one
car into that of the other,
reflectors,
The next example, Fig. 3, demonstrates an accident in which a car
ran off a wet asphalt road at a bend, At this point the road is flanked by wide
grass verges with a kerb on the east side, The curvature at the west verge
is 197 ft (precision t2 per cent). An interesting feature is that the centre
white line had been corrected recently and the former line, although worn,
was easily visible, The car's path coincides with the crown of the road
missing the advantage of the crossfall to the east of this (see sections Fig, 3)
The car was brought to a halt when its rear swung into a bus-stop signpost
breaking it off 12 inches from the ground (see Fig. 4).
The land around the Laboratory is quite flat and road gradients
rarely enter into accident scenes except near bridges or near the river
Thames, One site of particular interest from this point of view was surveyed
after a fatal accident. A southbound pedal cyclist carrying straight over a
road junction, Fig, 5, was overtaken by a lorry turning east, The cyclist
collided with the rear side of the lorry, was knocked down and died. At the
inquest, the lorry was stated to be travelling 6 feet from the kerb, The
radius of curvature of the nearside kerb varies from 130 to 110 ft at the
junction, The road was dressed with granite chippings and was in good
condition, Contours at 5-cm intervals are constructed for part of the road by
interpolation from spot heights plotted for three camera stations, The road
dressing was ideal for this purpose; individual chippings being readily
located on the negatives, The discrepancy in any ground point height taken
from separate stations has a 2-cm standard error, Sections AA', BB', CC
across the road are shown, Fig, 6, with heights plotted at ten times map scal
The camber close to the kerb varies between 1/6 and 1/8, A hump in the
road at section BB' is revealed, Fig. 7 shows the heights of the front wheels
computed for a lorry of this kind travelling 6 feet from the kerb, The
difference in wheel heights is also shown, It can be seen that as the road
rises it "tosses', '"pitches'" and 'rolls'", Just how much of this could have
been transmitted to the lorry body would have depended on the characteristic
of the suspension, and it is a matter of conjecture whether this movement
might have distracted the driver even momentarily,
The possible effect of road design on accident rate is particuiarly
marked in the next example, Fig. 8, This site, which presents some
interesting features not the least of which is its size, was covered from six
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