Rather than spending money on a new lens (decent glass is expensive!) I'd think about changing the perception of the people passing by and officers that might pull up to your spot. The yellow vest is a great idea but if you want to add to it think about a sign. If you often shoot that same location, you could spend a few dollars on a plastic A-frame sign with a nice clipart picture of a camera and/or some text like "photography in progress" or similar

This will likely change the mentality of people driving by so they recognize you as a photographer and not a terrorist pointing a big black tube at airplanes.