STEP WITH US into the not-too-distant future. It’s legal in Lexington County to drive through red lights after stopping and looking both ways. But in Kershaw County, no one can even turn right on red. In Richland County, the “unless otherwise posted” speed limit is just 20 mph, while in Charleston County, motorists must yield the right-of-way to bicyclists. And so on across the state — each county with its own particular set of “state” highway laws.

Drive at your own peril. If you venture outside your home county, chances are good you’ll violate a law you didn’t even realize existed. And pity the poor Highway Patrol troopers who are expected to keep up with all those one-county laws.

That’s the path the Legislature seems determined to send us on, unless the full Senate decides to acknowledge its responsibility for what’s called local legislation.

At issue is what the Legislature is going to do about Gov. Mark Sanford’s veto of a bill that expands the times and places people can drive golf carts on public roads in Richland County.

There’s a long story behind the bill, but essentially when the Legislature showed no interest in Rep. Todd Rutherford’s attempt to change the law statewide, he put up a local bill, which applies to only one county. By custom, legislators outside that county don’t vote on local bills, because if they did, then outsiders might vote on their local bills, in a way they didn’t like. Richland County legislators approved the golf cart bill, and Mr. Sanford vetoed it (as is his custom), not because it will cause chaos on our highways but because in all but the most extraordinary cases, the South Carolina Constitution prohibits laws that apply to only one county.

The House already has made clear that it’s not concerned about the state constitution or about the disturbing new precedent this bill sets, by extending the scope of local legislation beyond the tax and school matters to which they usually apply and into state highway law. Earlier this month, as is their custom, the 113 House members who don’t represent Richland County sat on their hands while the 11 Richland County legislators all voted to override Mr. Sanford’s veto.

And now the measure is before the Senate, where that body’s custom would require the 42 senators who don’t represent Richland County to vote the way their Richland County colleagues do on the veto override. But that custom has been coming under attack of late, and one senator, Charleston’s Chip Campsen, has indicated that he might break with that tradition on this measure. He should.

So should the other 41 non-Richland senators, every one of whom swore an oath to obey the constitution. And of course, the Richland County senators — John Courson, Darrell Jackson, Joel Lourie and Kay Patterson — should be among those voting to sustain the veto.

What we really need is for our senators, and representatives, to put an end to this “you scratch my back, I’ll scratch yours” practice of looking away when their colleagues thumb their nose at the constitution. They need to decide whether they want to write state law or local law, and if it’s the latter, they need to resign and run for city or county council.

Maybe all that is too much to ask for. But it shouldn’t be too much to ask that they not set this dangerous precedent. Our highways are already deadly. We certainly don’t need to make it impossible for drivers or police to keep up with the laws.