Legal Question in Employment Law in Pennsylvania

Not enough information has been provided to give you a definitive answer. I will assume from your question that this situation represents a change in your employment conditions.

You are allowed to quit your job and collect unemployment compensation if your employer makes a unilateral and substantial change to your employment conditions. Based on the information at hand, I believe that question whether the change is "substantial" could go either way.

Assuming your employer is paying travel reimbursement at the mileage rate set by the IRS, your argument becomes weaker. That rate is set to compensate you for fuel and wear/tear on your car. If your employer is not paying mileage reimbursement or is using a lower number, your argument becomes stronger because you can allege your total compensation has been reduced.