The House Oversight and Government Reform Committee held a hearing Thursday to dig in on the issue.
"Approximately 10.3 million people have admitted to driving while under the influence of illicit drugs in the past year," said Rep. Gerry Connolly, D-Va.
"From 1999 to 2010," said Rep. John Mica, R-Fla., "the number of crash victims with marijuana in their system has jumped from 4 percent to over 12 percent."
While all the congressmen agreed that driving under the influence of marijuana, or any drug, is not a good idea — they also all agreed there is one big problem with enforcing a legal limit — there's not enough scientific research.
"There's been very limited research actually conducted by the federal government addressing the relationship between marijuana usage and driving safety," said Connolly.
One of the witnesses at the hearing, Dr. Jeffrey Michael from the National Highway Traffic Safety Administration, said much more research is needed to gain a good understanding of the effects of marijuana on safe driving.
Currently 22 states, plus the District of Columbia, have legalized marijuana in some fashion.
There is no field sobriety test to look for marijuana in a person's system. Most of the research comes from blood tests.
The National Highway Traffic Safety Administration is partnering with Washington state to research the before and after data of drivers impaired by marijuana in a state that legalized the substance.