This evening, residents of Richland County can help shape the debate on a penny sales-tax referendum planned for Nov. 6.

County Council appears poised to put the question of a transportation sales tax to voters — a measure just slightly changed from two years ago, when voters barely rejected a local tax to pave roads; improve bus service; and add sidewalks, bike lanes and greenways.

This time, voters would be asked to impose a tax for 20 years. That would raise about $970 million for projects in Columbia and Richland County.

Here are a few details:

Why a sales tax?

Raising the sales tax on most purchases to 8 cents on the dollar would provide $45 million to $50 million a year, a stable revenue stream specifically dedicated to the county’s transportation system.

As it is now, the county devotes its share of state gas-tax revenues to pave and fix roads. That’s about $2.4 million a year, an amount many say is woefully inadequate.

Money for bus service comes from a countywide vehicle fee — $5 for a personal vehicle and $7.50 for a commercial vehicle — that appears on property tax bills each year. That raises about $1.6 million a year, an amount that won’t continue covering annual operating expenses, despite system cutbacks earlier this year. City residents chip in for transit twice, since they also pay a fee on their utility bills devoted to bus service.

As for walking and cycling needs, the county only recently completed its first suburban sidewalk project, and has not done any cycling or greenway projects. Those kinds of amenities don’t have a line item in the county budget.

What would the money buy?

Transportation planners Parsons Brinkerhoff established a list of projects representing the county’s top priorities. The list was compiled from public hearings and meetings with elected officials along with data on traffic congestion, land use, public safety and environmental effects.

The proposal before County Council is for 71 percent of tax proceeds to go to road projects, with 25 percent to improve bus service and 4 percent for pedestrian and cycling needs.

There’s also money in the package to publicize the referendum on the front end and manage the projects on the back end.

Who’s leading the discussion?

The Greater Columbia Chamber of Commerce has been onboard from the beginning, raising campaign funds and bringing together community groups that include the United Way, Palmetto Health, faith groups and construction and engineering firms. Groups of bus riders and cycling enthusiasts have been supportive, too.

A taxpayer group called Citizens Against the Tax Increase is certain to organize opponents if the council moves ahead with the plan for a 20-year sales tax. That group also objected that voters had no assurance the publicized projects wouldn’t be changed later.