The language of the easement (and perhaps its historic uses) will inform whether you can stop this type of use. Likely a utility easement cannot simply be turned into an access easement without your permission. You should make clear that you don't support or permit this use. If you can't work it out, you'll need an attorney. Don't simply ignore the issue or let your neighbor get his way. You're right to be concerned about your liability and property rights.
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An attorney, preferably one whose practice is mostly real estate law, should review the existing easement language and advise you on your alternatives. There may be other factors involved, but the recorded easement instrument is the most critical document here and will likely control the issue of whether or not the proposed general driveway access is permitted in addition to it creating a route for utility lines. As a general rule, the wording of most utility easements allow access only for installation, maintenance and repair of improvements related to utilities. A utility easement is not the same as a driveway easement and the courts usually do not expand uses much beyond those stated or implied in the easement as written.
Please keep in mind that this is not intended to create an attorney/client relationship. These are only general comments made without all the critical facts needed to fully form an opinion.
Easements can be a bit complex. When you say utility easement I start thinking that this is an easement given to or reserved by a utility company - like the electric company, or the city for sewer and water. An adjacent private landowner would not have the right to use this easement for a private purpose. My colleagues are correct that you need to read the prior easement documentation. The county surveyor's office might be able to help you as they would have access to historical documents that would show you not only the present plat map and recorded easements but historical details that preceded. Sometimes the right to cross someone's property can be based on historical rights of access. Sometimes it can be based on necessity such as when someone is landlocked and has no other choice. But your brief description above doesn't give sufficient facts. You will probably need to talk to an attorney to sort this out. http://www.portlandlegalservices.com
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