Add another D to the report card for the nation's most dangerous drivers: Drugged.

Drunk and distracted drivers have rightly raised of hue and cry, but more and more, those who patrol the highways are on the lookout for those driving under other influences.

Last week, Pennsylvania certified another 20 troopers and local cops as drug-recognition experts (DREs), bringing the state's total to 109.

New Jersey has about 120 troopers who have finished special training to distinguish drug impairment from alcohol involvement and various medical conditions.

There's an "epidemic" of abuse and misuse that includes illegal, prescription, even over-the-counter drugs, said State Police Sgt. Robert Tormo, who coordinates New Jersey's training program.

"It's scary to be out there sometimes," he said.

Even a seemingly harmless allergy medication like Benadryl can make some drivers dangerously drowsy.

Some people pop sleeping pills while behind the wheel.

"We actually see it fairly often," said State Police Cpl. David Andrascik, DRE programs coordinator for Pennsylvania. "Sometimes, they get off from work and they think they can take their Ambien on the way home."

Some Wall Street traders, for example, work such long days they hope to walk in the door and drop right off, Tormo said.

Not surprisingly, marijuana is the most common culprit, but law enforcement sees it all: heroin, PCP, OxyContin, Xanax, Valium, and dextromethorphan (DXM), a cough medicine ingredient that is abused, Andrascki said.

With so many drugs, and so many possible effects, intensive training is needed to make someone a drug-recognition expert.

Two weeks of classroom work is followed by field testing, which sometimes involves homeless drug abusers in Camden, who agree to be evaluated, said Tormo.

Symptoms vary greatly, since some drugs rev people up, while others slow them down, so officers have to pay attention to all sorts of indicators, either on the road or at a police station, such as pupil size, facial coloring, smells, behavior, speech, pulse rate, body temperature and blood pressure, Andrascik and Tormo said.

Another complicating wrinkle is that drivers can be impaired by medical conditions, such as having a stroke while driving or low blood-sugar levels due to diabetes.

Finding residue, paraphernalia or a container can be helpful, but often it's not proof of actual use, said out Lt. Steve Jones, spokesman for the New Jersey State Police.

A helpful field sobriety test is referred to as HGN, for horizontal gaze nystagmus. Basically, the suspect is asked to track an object like a pencil. Sober people can lock their eyes on it, even when it's far to one side. For those under the influence, the eyes are more apt to "bounce," Jones explained.

Making a suspect walk nine steps forward, turn and walk back not only tests balance, but attention, comprehension and multitasking, so it works with both drunks and drug users, Tormo said.

Urine and blood tests are often used for confirmation.

Neither state had hard statistics that separate DUIs that involve alcohol from those that don't, since all such violations fall into the same category.

Inebriation cases, though, seem to overwhelm the drug-related ones.

From 2 to 16 percent of DUI cases nationwide seem to be related to drug use, according to a 2009 National Highway Traffic Safety Administration report to Congress. The study, though, cited problems with obtaining clear and reliable data.

In Pennsylvania, arrests for driving while drugged have doubled since 2004, according to state police.

Since 2004, DREs in the state have evaluated nearly 6,000 people suspected of driving impaired by a substance other than alcohol.

Nationwide, about 10,000 people died in 2010 because of motorists driving under the influence of a substance, according to the NHTSA.

Contact staff writer Peter Mucha at 215-854-4342 or