THE control of road traffic by means of vehicle-actuated signals is making rapid progress. In a paper read to the Institution of Electrical Engineers on January 24 by Mr. T. P. Preist, the relative merits of the control of road traffic by traffic officers and by time-controlled signals are discussed. The great advantage of using traffic officers is that they are able to take advantage of any useful break in a heavy stream of traffic and so reduce the time interference to a minimum. A drawback is that they are not conspicuous; this could be reduced by mounting them on a raised platform or crow's nest, but even this is not always effective, and a driver in the rear has to deduce the signals from the movements of. the vehicles ahead. They also favour unduly horse drawn vehicles and stragglers. With automatic lamps the signals are highly visible and control the traffic of vehicles before officers could see them from the cross-roads. On the other hand, the system is quite inflexible and may lead to much waste of time. Although railway practice has provided much valuable information to designers of road traffic control, there is a great difference between the fixed path of the railway train and the haphazard paths of the road vehicle. Mr. Preist pointed out a useful analogy between the road traffic problem and the problems that arise in telephony. Both arts have to select and control particular paths from the total available and ensure the orderly passage of the chance traffic arriving on those paths. In telephony the ‘traffic’ is concerned more with areas than with, intersections, and future progress of road traffic control will probably lie in this direction.