General Liability Insurance provides:

This is coverage for an insured when negligent acts and/or omissions result in bodily injury and/or property damage on the premises of a business. Also provides coverage when someone is injured in the general operation of a business such as a pilot or escort car business. All General Liability policies exclude Professional Liability.

In the normal operations of a pilot or escort car business, (not including route surveys or height pole work) you could be accused of being negligent in the operations of your business.  This policy would provide defense costs for this exposure.  General Liability would be your basic coverage to protect you.  Usual required limits are $1,000,000

Professional Liability Insurance provides:

Liability created when an individual who offers services to the general public claims expertise in a particular area greater than the ordinary layman. Today, suits are frequently brought alleging that a professional, such as a insurance agent, physician, attorney, or CPA, or pilot or escort car operator has committed negligent acts or omissions in performing the purchased service.

This would be required if you are doing route surveys or height pole work. Since specialized training is required, and since you charge an extra fee for this service, it is classified as a professional exposure. If you fail to gauge the height of the load or the bridge and property damage occurs, that is an error of professional nature. If you choose the wrong route and there is property damage to a bridge or to the load, once again, professional liability would kick in. Your general liability or commercial auto would not provide coverage for this exposure. You would need Professional Coverage if you do either route survey or height pole work. Usual required limits are $1,000,000.

Commercial Auto Insurance provides:

Commercial Auto Insurance is a business insurance policy providing both property and liability coverage on any vehicle used in a business, which was designed for operation on public roads or highways. If you have a personal vehicle with personal insurance, there is exclusion in all personal auto insurance policies for business exposure such as pilot or escort car use.

This coverage provides insurance for bodily injury to someone that you might hit, and property damage to a vehicle or bridge or wall that you might hit with your vehicle. It does not provide coverage for the pilot car business operation. General liability and professional liability would provide coverage for that exposure. Commercial auto coverage, liability coverage covering the other vehicle you might hit would be the minimum you should purchase, usual limits are $1,000,000