Why doesn't MOW active grade xing signals?

Always wondered. The mow guys will always flag xings. Even though wheels are metal and should conduct electric when mow equipment or hi-rail vehicles go overs xings they do not drigger the flashers. Is it because they are heavy enough and the voltage is very low.

Most, but not all, machines and hy-rails are insulated from doing that and some will do it when the brakes are applied.

In addition, it might be because if there is any rust on the rails (or wheels), the electrical contact isn't good unless the load on the wheels is very heavy. I have read that with some lightweight operating equipment (such as the Budd self-propelled cars from ~50 years ago,some still in existence) crossing gates would not reliably be activated sometimes. So sometimes there were special instructions such as heavyweight equipment would have to operate first to shine the rails, and some lines didn't allow the cars at all. JS

pumpers wrote:In addition, it might be because if there is any rust on the rails (or wheels), the electrical contact isn't good unless the load on the wheels is very heavy. I have read that with some lightweight operating equipment (such as the Budd self-propelled cars from ~50 years ago,some still in existence) crossing gates would not reliably be activated sometimes. So sometimes there were special instructions such as heavyweight equipment would have to operate first to shine the rails, and some lines didn't allow the cars at all. JS

In further addition is that MOW vehicles such as hirail trucks are not legally trains and therefore do not have right of way over grade crossings as do trains. So automatic activation of grade crossing signals versus flag protection when the road is clear of vehicles is preferred. Also in the event of a collision the the MOW vehicle occupants are much more vulnerable than locomotive crews - and MOW vehicles are less obvious to motorists than trains, so greater probability of a collision.

Finally, the insulated wheels also prevent block signals from operating intermittently, not just grade crossing detection.

Fairmont motorcars (e.g., speeders) are specially built to not set off signals.

Most other MOW equipment also does the same, and in fact many railroad specify this in the rules.

It's pretty easy to do; you utilize a plastic cone shaped shim on the ends of the axles, which insulates the wheels from the axles, and then you use wood blocks in between the brake rigging, and the brake shoes.

End result is, the wheels are completely insulated from the frame/axle, and the vehicle wont set off signals.

MofW equipment does not shunt, simply because if it did, MofW could not work near a crossing.

MOW equipment does not reliably shunt so the crossings get flagged. If MOW equipment is working near a crossing it will cause the gates to sporadically activate so they are taken out of service while work is being done.