Testing the Limitation of Sighting Distances in the AS1742 Part 7 Standard

What was the issue?

Australian Standard AS1742 Manual of Uniform Traffic Control Devices Part 7 provides a method of calculating the sighting distance required to safely proceed at passive level crossings.

At the upper end of the sighting distances proposed (notionally greater than 750 metres) there was industry concern around whether or not a driver would be able to reliably identify a train and assess its rate of approach (i.e. speed) in order to take an informed decision regarding whether or not it would be safe to proceed across the level crossing.

What was done?

Field collection and analysis of data to assess sighting distance at which train becomes identifiable.

Estimation of the rate of approach of that train at distances greater than 750 metres (and up to 1500 metres).

What was found?

Field study participants’ detection of the presence of the train tended to improve with experience, but a similar trend was not observed for detection of the movement of the train.

Estimates of train speeds were very poor and participants were not able to accurately judge the approach speed of trains at any distances, with large underestimations at all distances.

It was not possible to determine a single limit beyond which the formula cannot be relied upon to make reliable judgements based on train presence and speed. For example if the sighting distance was 580 or 780 metres, all participants would have detected the train as soon as it became visible for each of their trials but at sighting distances of 750 and 1,450 metres 85% of participants would have detected the train as soon as it became visible.

Risk assessment, taking into account this sighting information and other relevant factors described in the standard’s appendices, is required to evaluate whether the required sighting distance provided by the formula can be relied upon or whether alternative arrangements for heavy vehicles should be provided.

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