A long-sought way of protecting Metrobus drivers from harm has run into problems.

Many of Metro's buses won't accommodate optional bus shields that union officials have wanted for years. The agency's latest New Flyer models cannot fit the shields, which fold open if drivers do not want to use them, because the plastic shields would get in riders' way, according to Metro.

Metrobus and security officials said that's not a problem because about 20 bus operators told them they don't want the shields anyway, worrying the shields are confining and wouldn't help them if needed.

But the union representing about 2,500 bus operators said the agency is relying on too small a sample size of opinion and should add the shields to buses.

"We do want the option of extra protection," Jackie Jeter, president of the Amalgamated Transit Union Local 689, told reporters Thursday.

She said the shields may not be necessary for a 400-pound male bus driver but a small woman operating a bus at 2 a.m. may find it adds security. "I've walked the walk," she said, recalling how when she drove a bus 30 years ago she knew she would be OK if she had trouble on the 30s line when she reached Capitol Hill due to the federal police stationed there.

"Things have been happening on buses since Jesus was born," Jeter said.

Crime on Metrobuses has become a renewed concern after three homicides occurred in 2012.Serious crimes on Metrobus rose in 2012, with an average of 11 crimes per month, compared with seven in 2011, according to a new report. Most of the crime occurred in the District.

Bus drivers reported being assaulted more frequently, as well, with 74 cases from January through mid-December, compared with 65 for the same period in 2011.

The issue came to a head in the fall, when Metro proposed cutting some late-night service in Southeast D.C. because of teens throwing rocks at bus drivers. The agency backed down after outrage from D.C. officials.

The union has sought the bus shields for years. An earlier model wastested in 2008. Metro has since installed protective shields on 52 of its approximately 1,500 buses. But that number was scaled back from 301 in December 2011 after D.C. Councilwoman Muriel Bowser raised concerns about the shields sending the wrong message to riders.

Now, Jeter said, if the new buses cannot be retrofitted with them, the agency should put the money into other resources to protect operators. Jeter said she would like Metro to give drivers conflict resolution training, which she said she has requested for years. She said she also would like to see more uniformed police on local buses to deter crime.