3 eye 
Tuct 
rs 
‘hat 
ja 
tail 
3 of 
one 
a car 
y wide 
erge 
itre 
rn, 
rig, 3) 
ost 
rveyed 
ra 
list 
t the 
-oad by 
road 
ken 
, CC 
ap scal 
he 
wheels 
ad 
lave 
ristics 
ent 
irly 
n six 
camera stations. It is a road junction where the main road, approaching 
London from the south west, forks left deviating by about 40° while the 
right fork carries straight over, The main road has four lanes to the 
south west and three lanes to the north east with a joining 2-lane section, 
which is about 400 feet long, The appearance of the scene to London-bound 
traffic is shown in Fig, 9 where the possible distraction of advertisement 
hoardings, the difficulties of reading road direction signs and markings and 
of recognising the character of the junction from a distance are made clear, 
In the period lst January, 1956 to 15th July, 1959, local police reports 
show that 60 accidents have occurred on this site of which 42 took place at or 
near the main fork, In eight of these drivers' indecision is believed to have 
played an important part, another ten involved some indecision and/or lack 
of care, Seven of these accidents have been studied in detail by the 
Laboratory, These studies support the conclusion that the accident 
potential of this road junction can be reduced, (It is understood that this 
junction is to be redesigned and will include a roundabout, ) 
A comparison was made between this survey and a dyeline copy of a 
conventional 1/480 scale survey (Fig, 10) made of the site in 1936 by the 
county engineer, No material topographical change in the site appears to 
have been made since then, Kerb line differences amounting to 2 per cent 
were found. It must be noted that the whole plot was compiled from six 
pairs of photographs using only minor control points and, although the errors 
in the dyeline copy were unknown, these were probably about 1 per cent. The 
2 per cent difference is not inconsistent with the possible accumulation of 
error in such a compilation, 
In Great Britain when law court proceedings follow a road accident the 
police are often required to produce a true scale road plan. This is done 
by a plan drawer', normally a constable engaged on general duties, who 
indicates distances of critical importance, 
Fig, ll is reproduced from a dyeline copy of such a plan of the 
above-mentioned site and is included for comparison with the other surveys, 
Even the most casual comparison of Figs, 8, 10 and 11 (taking Fig. 10 as 
the standard) shows that the stereophotogrammetric equipment employed 
yields maps whose precision exceeds that normally accepted in court cases. 
The routine use of photogrammetric equipment by the police in 
Britain, however, would almost certainly require a change in legislation, 
The alternative, of up-holding photogrammetry as a valid science of 
measurement in each law case, can be both time-consuming and extremely 
expensive, (17) 
Stereophotogrammetry has been used to estimate car damage. The 
following example, while not exceptionally spectacular, adequately demon- 
Strates some essential points, The two views shown in Fig. 12 were taken. 
Plots, at 1/25 actual scale, were compiled at 10-cm height intervals; two 
of these plots are shown in Fig, 13, The car outlines are dotted, the contour 
lines are at 90 and 130 cm from the ground. Gaps in the contours are due to 
lack of detail, In fact, extensive plotting was possible only because the car 
Was covered with discrete rain drops. Highlights and other reflections from