If you read the linked article:
Here’s the problem: With no Breathalyzer (now the Alcotest) to measure marijuana impairment,
convictions for stoned driving rely on the observations of thoroughly trained drug recognition experts (DREs). Experts across the spectrum, from police chiefs to Triple-A officials to DUI attorneys, agree that there needs to be a substantial increase in DREs as marijuana becomes more prevalent across the state.
Somebody has to pay for these hires and their training. It ain’t cheap.
“Right now you have about 500 officers (in New Jersey) who are trained as a DREs,” Zebrowski said. “This is a very specialized area, and we don’t want to dilute that area by forcing other officers into that program. We need to be able to continue to keep it specialized, which makes it an expensive proposition for small towns, and even large towns will be stretching their resources.”