Each traffic signal shall have an emergency vehicle detector system which shall conform to the details shown on the plans and these special provisions.

Each emergency vehicle detector system shall consist of an optical emitter assembly or assemblies located on the appropriate vehicle and an optical detector/discriminator assembly or assemblies located at the traffic signal.
Emitter assemblies are not required for this project except units for testing purposes to demonstrate that the systems perform as specified. Tests shall be conducted in the presence of the Engineer as described below under “System Operation” during the signal test period. The Engineer shall be given a minimum of 2 working days notice prior to performing the tests.
Each system shall permit detection of 2 classes of authorized vehicles. Class I (mass transit) vehicles shall be detected at ranges of up to 300 m from the optical detector. Class II (emergency) vehicles shall be detected at ranges up to 550 m from the optical detector.
Class I signals (those emitted by Class I vehicles) shall be distinguished from Class II signals (those emitted by Class II vehicles) on the basis of the modulation frequency of the light from the respective emitter. The modulation frequency for Class I signal emitters shall be 9.639 Hz ± 0.110 Hz. The modulation frequency for Class II signal emitters shall be 14.035 Hz ± 0.250 Hz.
A system shall establish a priority of Class II vehicle signals over Class I vehicle signals and shall conform to the requirements in Section 25352 of the California Vehicle Code.

Webasto AT2000ST Service Manual

Webasto AT200ST Service Manual (LIT9010439B)



Interesting note on this heater:

Recently ran some bad fuel through mine and unfortunately found out that the fuel metering pump does NOT like ‘thick’ fuel or algae running through it. These are often heater-specific fuel metering pumps and sealed units.  Acquired a replacement on e-bay and upon installing it found that the heater was throwing a glow pin fault code. Ran the diagnostics to find that the glow pin resistance was appearing ‘too low’ to the heater (even though it still turned glowing hot) so it would shut down.


I first found that there was a direct short showing between ground and the glow-pin source (through a FET to +12v). After analyzing the control module, I found a reverse protection diode had failed to short (probably the product of me trying to investigate the glow-pin operation and shorted/powered something). I replaced this with the reverse protection diode for the fuel metering pump and used a misc. SMD diode that I had on-hand to replace the failed one for the metering pump (a much less sensitively measured device). Now that the controller wasn’t seeing a short, I merely had to be concerned with the high (.6-.9ohm) resistance of the glow pin upsetting the controller. Book specifies somewhere around .4ohm.

I added two 21W light bulbs (an increased 2.4A load @ 12V…about 29W) and found that it didn’t complain about the resistance. I figure this fix will only last so long as the glow pin apparently is showing sings of giving up the ghost. Not very impressive for a heater that has less than 100hrs on it. The proper ‘fix’ if the glow pin is actually good (fault with the heater’s measurement circuit) would be to install a couple 15-20W 20ohm resistors in parallel to shed the load in a non-illuminating way.


Photos of the Webasto AT2000ST Control Module