National Academies Press: OpenBook

Traffic Signal Preemption at Intersections Near Highway–Rail Grade Crossings (2017)

Chapter: Chapter Eight - Conclusions and Suggestions for Further Research

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Suggested Citation:"Chapter Eight - Conclusions and Suggestions for Further Research ." National Academies of Sciences, Engineering, and Medicine. 2017. Traffic Signal Preemption at Intersections Near Highway–Rail Grade Crossings. Washington, DC: The National Academies Press. doi: 10.17226/24769.
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Page 39
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Suggested Citation:"Chapter Eight - Conclusions and Suggestions for Further Research ." National Academies of Sciences, Engineering, and Medicine. 2017. Traffic Signal Preemption at Intersections Near Highway–Rail Grade Crossings. Washington, DC: The National Academies Press. doi: 10.17226/24769.
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Page 40

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39 chapter eight CONCLUSIONS AND SUGGESTIONS FOR FURTHER RESEARCH The most important conclusion from this synthesis is that the state of the practice does not adequately reflect state of the art capabilities. Although some highway and railway agencies use advanced capa- bilities, as demonstrated in the case examples, the majority of surveyed agencies (55%) use a simple, two-wire preempt at their highway–rail grade crossings; and of those agencies using two-wire preempt, 58% use normally closed circuits. This two-wire preempt circuit conveys no more information to the traffic signal controller than was available when track circuits were first used to preempt traffic signals. The most significant innovation that is widely used by railway agencies is a constant warning time (CWT) system (or grade crossing predictor), which improves the consistency of warning times in most cases, but is not able to address variability at locations with trains that accelerate or deceler- ate on the approach circuit. However, even this innovation is used by 64% of surveyed agencies at new or upgraded locations. Improving practices has been difficult because of the multiple agencies involved, their diverse perspectives, and different business practices. For highway agencies, highway–rail grade crossings are a small part of practice, and the survey reveals significant gaps in technical understanding. Many surveyed highway agencies indicated a lack of understanding about topics such as gate-down, island circuit, “smart” recovery strategies, second- train-coming logic, and accommodations for train stations near crossings. The lack of technical under- standing is compounded by the fact that there is limited technical guidance and no standard for the traffic signal interface hardware to interconnect highway and railway control systems. Furthermore, state agencies sometimes defer to local agencies regarding traffic signal operations at highway–rail grade crossings, resulting in widely varied practices. Although the FRA encourages railway and highway agencies to coordinate joint inspections to verify that railway crossing warning systems interconnected to traffic signals function properly, the survey indicates that few highway agencies coordinate inspections with railway agencies. There are several initiatives that could lead to improved safety and operation of highway–rail grade crossings. First, identification and research of key limitations and conflicts in current opera- tion would likely result in a better understanding of how to operate highway–rail grade crossings in a variety of operating environments. Issues that might be addressed in future research include: • Clear definitions of terms • Concept of operations • Traffic signal operational concepts • Traffic signal operational strategies • Alternatives to truncation of pedestrian clearance interval • Count-down pedestrian signals • Advance preemption strategies • “Smart” recovery strategies • Second-train-coming logic • Supervised circuits • Use of multiple preempts • Use of pre-signals • Use of queue cutters • Use of blank-out signs for turn restrictions

40 • Strategies near train stations • Coordination with railway agencies • Periodic inspections • Use of traffic signal performance measures • Training of staff (including contractors). Second, guidance and training would likely bridge gaps in understanding and improve coordina- tion between railway and highway agencies. Training would include both railway issues and highway issues, regardless of the audience. Third, improvement of the interconnection between the railway and highway is currently limited by the lack of a traffic signal standard that defines the minimum functionality for interconnection hardware. Using a systems engineering process, a standard could be produced that considers how a traffic signal is to operate in various operating environments.

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TRB's National Cooperative Highway Research Program (NCHRP) Synthesis 507: Traffic Signal Preemption at Intersections Near Highway–Rail Grade Crossings documents the current practices of traffic signal preemption deployed at intersections adjacent to railway grade crossing in both the United States and Canada. The study provides information on practices dealing with traffic signal preemption, maintenance, funding, and operations.

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