The Cold Spring Shops position on highway construction is that widening existing roads is often not cost-effective.
There's something called the Law of Peak Expressway Congestion that suggests road improvements divert traffic from other roads, until travel times are the same on the improved road as they are on the unimproved roads. (Indifference at the margin, anyone?) An elaboration of the law suggests that additional capacity shortens the duration of the peak subject to the same indifference condition, which makes sense as long as the total volume of trips stays the same, but a shorter crush hour serves as an inducement for more people to relocate.
A recent guest column in the Milwaukee Journal-Sentinel, in objecting to providing additional lanes on the original East-West Freeway, makes precisely that point.
Even though people are driving less, it's possible to get them to drive more. How? Build more lanes. Whenever capacity is expanded, more driving is induced. Don't take it from me; listen to the most recent newsletter from HNTB — one of the nation's biggest road builders:

"Conventional wisdom suggests that we simply need to build more capacity. Adding lanes, however, will never fully solve the congestion problem. When new general-purpose lanes are built, they immediately fill up. They may help compress rush hours slightly, but the congestion problem remains."
Precisely.  Ribbon-cuttings are fun.  Implementing policies that work, less so.
The "most effective" policies are also those most difficult to sell to the public: peak-hour pricing of all expressways and arterial streets, possibly including satellite tracking of vehicles to enforce time-of-use tolls (invasions of privacy be hanged?); higher gasoline taxes (conscripting soccer moms into the Pigou Club?); expressway expansion in the form of high-occupancy toll lanes only; and surcharges on long-term parking in the morning. The policies favored by technocrats tend to be "very ineffective": concentrating jobs in clusters in new-growth areas; driving bans based on license plate numbers; zoning to put jobs closer to houses; higher automobile licensing fees; growth limitations.
To his credit, the columnist shows the garlic to the vampire.
If needed, use price signals to control traffic. One example would be to charge large trucks a fee for using the freeway during peak congestion — that would send a signal to use an alternative route or an alternative time, reducing congestion on the highway. There are many other non-structural, cost-efficient ways to better manage traffic. This would all cost a lot less than adding a lane.
The problem with a special toll for trucks is that National Avenue is available for the elephants to pound to pieces. It's a start, though: a political coalition of environmentalists and libertarians and investors in freight railroads can find common ground in identifying just how much corporate welfare is present in the ability of the truckers to cause havoc with 53 foot trailers everywhere.

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