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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 highwayârail 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, highwayârail 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, âsmartâ 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 highwayârail 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 highwayârail 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 highwayârail 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 ⢠âSmartâ 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.