ANALYSIS OF RAILROAD HORN DETECTABILITY

The Acoustics Facility of the Volpe National Transportation Systems Center (part of the Research and Special Programs Administration of the U.S. Department of Transportation), in support of the Federal Railroad Administration, is conducting safety research to evaluate the effectiveness of various methods of reducing the number of accidents and resulting casualties at highway-railroad grade crossings. As part of the research, the effort reported here evaluates the probability of detecting railroad horn systems used as audible warning for motorists at highway-railroad grade crossings. To evaluate the detection probability, three sets of acoustic data were collected: (a) acoustic characteristics of railroad horns, including sound level and directivity; (b) insertion loss of motor vehicles; and (c) baseline interior noise levels of motor vehicles. These data were used to determine the warning-signal-level-to-interior-noise-level ratio inside the motor vehicle at the minimum distance that would give the motorist sufficient time to react and avoid a collision. Signal detection theory, which incorporates the motorist\u27s prior expectations of encountering a train, is then applied to estimate the probability of detecting three currently used railroad horn systems at active and passive grade crossings

Reinforcement context and pacemaker rate in the behavioural theory of timing

In the present experiment, an attempt was made to extend the base of evidence for the assumption of the behavioral theory of timing that pacemaker rate is determined by reinforcement rate. Pigeons discriminated the first half from the second half of a 50-sec trial in a free-operant psychophysical procedure. Left-key responding was reinforced at variable intervals during the first 25 sec, and right-key responding was reinforced at variable intervals during the second 25 sec. The rate of “extraneous” reinforcers delivered at variable intervals following responses to a center key was manipulated independently of performance in the temporal discrimination. Quantitative estimates of pacemaker rate were not directly proportional to extraneous rate of reinforcement, whether extraneous reinforcers were available during the intertrial interval, the entire session, or the trial only. Instead, estimates of pacemaker rate were inversely related to the rate of extraneous reinforcement, which suggests that pacemaker rate is determined by the ratio of the rate of reinforcement for the timing response relative to other sources of reinforcement