The ITE Preemption of Traffic Signals Near Railroad Crossings manual provides excellent guidance determining the need for preemption. In Texas, the Requestor shall apply at least one of following four methods to determine queue lengths.

Anecdotal Evidence
Field Observations
Queue Length Calculations
Traffic Simulation Modeling

Local highway authority staff, police, train operators, or train dispatchers may note queuing issues and can help initiate further investigation such as timing of field observations. However, the CSD may occasionally be shorter than the length of the design vehicle. In this case, it may not be necessary to further review the queue lengths since vehicles are already likely to queue within the CSD and naturally encroach the tracks when doing so. Various queue mitigation strategies should be implemented to provide the on-track queue prevention.

The Requestor should complete field observations whenever possible to inform the diagnostic team with site specific data. Video surveillance can be used to review a location over an extended period and note motorist behavior and queuing at various times of day.

Locations where either the intersection, traffic signal, or grade crossing are not yet operational may necessitate queuing calculations to estimate queue lengths. The Requestor should refer to the ITE Preemption of Traffic Signals Near Railroad Grade Crossings manual for additional details regarding queue length calculations.

When determining queue lengths at locations where the crossing or the intersection is not yet operational, the Requestor may also use traffic simulation modeling. Software running the current version of

Highway Capacity Manual

calculations or a traffic simulation model are acceptable as long as 95th percentile queue length are provided. The Requestor should also consider factors such as vehicle composition, platooning due to nearby signals, potential back-to-back preemption events, train length, and overall time in preemption to accurately estimate queue lengths.