Traffic Signal Preemption Near Rail Crossings

Where a grade crossing is in proximity to a signalized intersection, a traffic queue from the intersection may extend onto the track resulting in a motorist being stopped on the track.

At such locations, traffic signals are typically interconnected with the train-activated warning systems. The design and operation of the interconnected systems is generally referred to as “railroad preemption”.  The purpose of railroad preemption is to allow motorists to move away from the track prior to the arrival of the train and to restrict movements towards the track.

Preemption Timing Worksheet

A primary purpose of railroad preemption is to ensure that a vehicle stopped on the track will have sufficient time to move off the track prior to arrival of a train. The preemption worksheets can assist in calculating railroad preemption timing.  The forms require site-specific information such as the distance across the tracks and roadway design vehicles.

The preemption worksheet developed by Los Angeles Department of Transportation (LADOT) is commonly used in California.  The California Department of Transportation (Caltrans) has also developed a worksheet.  Nationally, a commonly used worksheet is published by Texas Department of Transportation (TxDOT).

CPUC Authorization

CPUC General Order 75-D, Section 11, discusses requirements for CPUC authorization of modifications to rail crossings, including “any changes that may affect interconnections with adjacent traffic signals, or any other modification that may impact the safety of the at-grade crossing.”  Typically, modifications at a specific location are authorized through the process discussed in General Order 88-B.  Modifications may also be authorized through a formal proceeding at the Commission.

Design Documentation

For a project involving railroad preemption, the following design documentation should be prepared to the extent applicable:

• Preemption Timing Worksheet:  Worksheets should be one of the three forms: LADOT, TxDOT, and/or Caltrans.  When included as part of the authorization request, the timing should be the actual proposed timing. 
• Preemption Calculation Measurement Exhibit: Exhibit shows the Minimum Track Clearance Distance (MTCD), Clear Storage Distance (CSD), the longest pedestrian crosswalk distance and other distance parameters shown in the preemption worksheet.
• Traffic Signal Plan: Scaled exhibit showing the location of existing and proposed traffic control and railroad warning devices with the following information:
  • Phase Diagram 
  • Phase sequence upon preemption (or comparable description)
  • Traffic signal masts and signal heads
  • Part-time turn restriction (Blank-out) signs (if used)
  • Information on railroad interface panel (if used)
  • Preemption Interconnect Wiring Diagram
• Railroad Preemption Request Form (if applicable)
• Design-Vehicle Turning Template (if applicable)

Detailed References

Minimum requirements for railroad preemption are discussed in the California Manual on Uniform Traffic Control Devices (CA MUTCD), published by Caltrans. Refer to Parts 4 and 8.

The design of railroad preemption often involves details beyond what is discussed in CA MUTCD.  The references below provide additional considerations regarding railroad preemption.

• “Highway-Rail Crossing Handbook, 3rd Edition”, FHWA-SA-18-040, Federal Highway Administration (FHWA), 2019.
• “The Preemption of Traffic Signals Near Railroad Grade Crossings, 2nd Edition, an ITE Recommended Practice”, RP-025D-E, Institute of Transportation Engineers (ITE), 2021.
• “NCHRP Report 812: Signal Timing Manual, Second Edition”, National Cooperative Highway Research Program (NCHRP), 2015.

Contact RCEB for Additional Details

Please refer to RCEB contact information for territory assignments.

For inquiries regarding railroad preemption, please contact Chi Cheung To or Kevin Schumacher.  For specific project review, please contact the appropriate RCEB engineer for the project location as identified in the territory maps.