Some political junkies think medicare, social security for seniors and similar heart-and-mind issues are the "third rail" of politics - akin to the third rail on subway tracks - because any politician who touches them will be electrocuted.
But the real third rail in North American politics is free roads.
Every once in a while, an environmentalist without street smarts forgets this (brain clouded by too much car exhaust while biking, perhaps) and gets fried PDQ.
That's what happened to Gord Miller, Ontario's environment watchdog, when his annual report suggested road tolls as a way to reduce carbon emissions as well as cut through Toronto traffic jams, which create smog without any benefit of movement.
Needless to say, most politicians howl at the idea that drivers should pay for road use, while self-sabotaging green types talk up tolls as a way to pay for public transit - the very fate that drivers most dread and will cuss in traffic for hours to avoid.
Traffic jams don't just happen on the road; they express the road map of transit planners' minds.
Toronto's notorious congestion - estimated to cost the economy up to $6 billion a year in lost productivity as truckers and others sit in traffic - testifies to the power of linear thinking and one-track minds on the left and right, green and brown.
The problem starts, says Martin Collier of Transport Futures, with the term "road tolls" rather than his preferred "road pricing." There are countless ways to price roads, he argues, tolls being but one and far from the most useful.
Roads can be free for users, as they are now, though Toronto spends $100 million a year repairing them. Or they can be priced in tolls by the hour used (less for non-rush-hour times, for example); by the number of passengers (those with two or more passengers get the fast lane, for instance); at parking lots (perhaps a $1 levy added to parking fees); in gas taxes at the pump; or by car insurance (higher rates for people who drive to work) - to name only a few options.
One way or another, the full cost of roads - their construction, upkeep and eco impacts - have to be paid for. There's no such thing as a free road.
We now pay almost exclusively via tax dollars, pollution and the currency of lost time. In economics, traffic jams are just the predictable pattern of long lineups whenever prices are discounted below real costs.
But the biggest of linear-think jams comes from failing to see that access is what people need, not roads. In a lakeside city like Toronto, for example, a lake shuttle from Oshawa to Hamilton could be safer, less polluting and get people closer to downtown than a train or subway across underpopulated suburbia. It just takes thinking outside the lines.
Lake Ontario, which shuts off southern access and forces all incoming and outgoing traffic onto half the space available to many other cities, is also telling people we should work closer to home. The fact is, running a transit system designed to get commuters to and from work is a losing proposition; too much costly infrastructure for too few trips during too few hours. So the more transit is based on many different kinds of trips - shopping, visiting, going to the gym, etc - the more effective transit policy can be.
Nonetheless, the real goal should be getting people out of cars and onto sidewalks, not onto transit, which rarely competes with cars for time.
Other reasons for road pricing include raising revenue so the city can reward employers for allowing home offices, and providing grants for proposals to increase walkability.
But the easiest way to embed road avoidance is through changes to the food system, which is many times easier to alter than our attachment to cars. About a fifth of car trips are for food shopping. Most of these could be eliminated by walking to good food retail on main streets.
Encouraging food stores on main drags, however, requires city planners to change their priorities and develop new mechanisms of enticement. Food retail is not only an essential service but also the kingpin of planning itself; you can literally construct a neighbourhood around it, since it always draws people.
And if perpetrators of traffic jams on highways were to be hunted down, long-haul food trucks bringing in about 90 per cent of our food supply from an average 2,000 miles away would be high on the list.
Since few incoming food trucks hail from companies that pay local or regional taxes for road construction, food trucks are the ultimate free-riders. They could be charged a hefty fee for daytime use and a smaller one for nights. The fee should be set to even the playing field for regional farmers who don't have to go the distance.
A look at the long term reminds us that one-third of the city is pavement - the available farm land of the future. Parking lots, underused for most hours of the day, with no alternative use, are a sheer waste. Researcher Brian Cook and I once Google Mapped city lots and were amazed at how many could be converted into 40-acre farms producing for walk-by traffic.
If Mayor Ford were thinking of new ways to avoid car wars, he might even use revenues from parking fees to fund affordable housing in the downtown so fewer people would have to commute to the core to work. Affordable housing and local food are the best trip-avoiders in the biz.
Scream though many will, there is no long-term evasion of road pricing. The issue is whether that money will be invested in trip avoidance or trip creation.