I wonder if there are trolls in St. Louis.

Actually, no. I’m not wondering that. I’m wondering if I’m becoming a troll. I’m looking at a picture of St. Louis’s Poplar Street Bridge, and my thoughts might be described (by others, anyway) as trollish.

We know less for sure about trolls than we do about Nessie or Sasquatch. According to Tolkien, trolls turn to stone in daylight. I’m out in the day, sometimes (walking my cell phone), and haven’t turned to stone yet. More to the point, from the classic Norwegian folk tale, “Three Billy Goats Gruff,” and other stories I’ve read to my daughters, I’ve learned that trolls don’t like people — or goats — crossing bridges.

Now, let me go on record: I’m all for people crossing bridges. (Goats too, though I can’t say I’ve seen many queued up in traffic.) But my fear is this: some people might misinterpret a certain notion I have about bridges. Some bridges, I’m thinking, shouldn’t be free. Tolls should be charged to go over a few bridges, at least some of the time.

And since nearly everybody wants to drive over bridges without charge, I’m afraid that nearly everybody will begin to look at me like the greedy troll that the third Billy Goat Gruff handled so effectively.

Which brings me back to St. Louis’s Poplar Street Bridge.

That bridge often gets clogged — the traffic bogged down — with the 120,000 cars that travel it per day. You don’t have to live in Los Angeles or New York City to know what a traffic jam is. Commuters across the nation now nod their heads: We know all too well what the citizens of (and visitors to) St. Louis, Missouri, and East St. Louis, Illinois must endure.

But a suggestion by a think tank in Missouri might cause a few heads to shake.

The notion? Make the Poplar Street Bridge a part-time toll bridge.

Southern Illinois University economist R. W. Hafer, writing for the Show-Me Institute, does more than merely recommend charging tolls at high traffic times. He argues that building another bridge to ease traffic congestion might do just the opposite. Why? By making commuting easier it would effectively lower the cost of commuting. When costs go down, demand grows. Demand, in this case, is more use, greater traffic over the river, which could even go so far nudge people off of public transit to drive their cars more.

Don’t get me wrong, I’m all for roads. And I oppose those who do their darndest to make traffic worse, so to encourage mass transit. But Hafer has a point here.

Placing a price on rush-hour bridge travel would encourage commuters to economize. Some would postpone their trips to off-peak hours; others would even make the trek over the Mississippi earlier. Why? Just to avoid tolls.

And with these shifts in driving behavior, the drive becomes easier for all.

By not charging tolls we turn bridges into institutions like the old “commons” in England . . . commonly owned land, free for all farmers’ cattle and goats and such.

A free and easy life. Sounds idyllic, no?

The trouble with this policy, as a very different economist famously noted a century or more ago, is that each farmer sees an advantage to let his livestock overgraze the land. After all, if he holds back his cattle and his goats, other farmers will simply use up the meadows before him. It becomes in his interest to overgraze first. Continued...