n its 
g ome 
on a nation-wide scale. Details of these investigations and of the British study 
have been given elsewhere, (1-4) 
The Laboratory's team, which is informed by the police of an accident, 
has a car waiting which enables it to reach the scene quite quickly, and if 
prompt warning has been given this might be within a few minutes of the 
accident happening, The team attempts the collection of all the information 
considered relevant to the accident. This involves, among other things, 
assessing vehicle damage, observing road marks and other road features, It 
is understandable that under pressure of limited time, imposed by salvage 
removal of damaged vehicles and rapid clearance of the road by the police for 
traffic, valuable information may be irretrievably lost, Indeed under such 
conditions it is difficult, using a tape, to carry out adequate measurements of 
the, accident site, measurements which are critical in estimating vehicle 
positions and transient marks on the road, 
This situation is somewhat ameliorated by taking conventional 
photographs with a high quality press camera to supplement the team's more 
general observations, Nevertheless a complete and precise location of 
vehicles and other features cannot be obtained by these means, 
Methods for the approximate restitution of this kind of accident 
photograph are well establishedU?- 10) pu these assume that the ground is 
perfectly plane and the planimetric errors which result when the ground is 
not flat are not always acceptable, For example, the width of a 30-ft road 
with a 1/20 curved camber could be underestimated by more than 12 per cent 
using these methods, 
In 1956, with the co-operation of University College, London, the 
Laboratory began trials with a stereometric camera designed by Wild, This 
camera, the C, 12, and its associated Autograph, the A. 4, have been adequately 
described by Zeller, (11) This and similar equipment of other manufacture 
have been used successfully for terrestrial photogrammetry and, in 
particular by some European police forces, for traffic accidents. (12-15) 
But the investigation of accidents by the Laboratory differs in many 
respects from that of the police. The emphasis, in the accident team's 
enquiries, is on finding the course of all events in a road accident; the 
determination of personal blame, which is a prime aim of police investigations, 
is taken on par with other contributory factors, The Laboratory's use of 
photogrammetry, therefore, is directed not only to depict an accident scene 
but also to illustrate such factors in road topography as may have contributed 
to its occurrence, 
Procedure in the field depends on circumstances but in general the 
immediate vicinity of an accident is photographed as soon as possible after it 
has occurred and a more extensive survey is carried out, of the whole road 
8Cene, later under less hurried conditions, 
The first example, Fig. l, illustrates some of the difficulties involved. 
The Bite can be reached by the accident team within 9 or 10 minutes of an alert, 
Itís a T-junction, the surface is concrete laid out in slabs, the main road has a