Too many people spend time in Philadelphia's jails for no good reason.

It's not that the inmates are innocent, necessarily. But the city's prison system is crowded with people who are awaiting trial for relatively minor offenses and can't post bail immediately.

On any given day, less than 25 percent of the more than 8,000 inmates in city jails are convicted criminals serving sentences. Most of the others being held will be released within a week, when they raise bail.

This inefficiency, known for years, was clarified by a valuable report from the Pew Charitable Trusts. It underscores the need for the city, the District Attorney's Office, and the courts to step up their efforts to streamline bail procedures and further reduce expenses.

The cost to taxpayers for the city's prison system is enormous. In fiscal 2009, Philadelphia spent about $290 million on prisons, including benefits for employees. That's about 7 percent of the city's general- fund budget. Over the last 10 years, the department's budget has doubled.

The inefficiency of the city's prison system is stark when compared with those in other cities. Cook County, Ill., which includes Chicago, has 31/2 times more residents than Philadelphia. But it spent about the same amount on prisons last year.

Pew's researchers found that Philadelphia's high prison population isn't due primarily to crime trends. It's within the control of public officials.

There are many factors to address, including the length of time it takes to resolve court cases in Philadelphia. About 75 percent of cases are unresolved after three months, often resulting in defendants' serving more time in prison than the eventual sentence specifies.

One bright spot is the recent reduction in the city jail population by about 1,500 inmates, due in part to a pact with the state to transfer some prisoners to state facilities.

District Attorney Seth Williams aims to streamline the process of charging defendants to weed out charges that aren't likely to result in convictions.

Another solution is the plan to create a "day-reporting center," where nonviolent defendants who would otherwise be in prison would report daily for supervision. This system, used in other cities, allows such people to remain in the community at far less cost to taxpayers.

The trick, as Pew points out and city officials are well aware, is to reduce costs and inmate population without sacrificing public safety. It requires effective screening and careful adherence to sensible guidelines.

But as this new report notes, other jurisdictions can and do succeed in making their criminal-justice systems more efficient and less costly.